# Sticky  GTO Gear Ratio's



## geeteeohguy (Feb 2, 2008)

Hi. I'm posting a new thread because I didn't want to hijack another thread that this subject came up on Gear ratios. I was bragging about my "racing" days, and gear ratios were mentioned. The following is some information that I have learned over the years, and the following opinions on gear choice are my opinions and nothing else. I am no engineer. 

I've run GTOs over the years with ratio's from 2.56:1 to 4.56:1. Stock early GTOs with stick shift usually came through with 3.55 gears, and auto cars had 3.36 gears standard. The 3.55 (4-Series) carrier could accommodate gears from 4.88 or so down to 3.36. The 3 series carriers could accommodate gears from 3.23 down to 2.51. I found that "back in the day", with cheap gas and road noise a fact of life, the 3.55 gears were okay.....the '66 tended to be running about 3200 rpm at 70mph....right in the power band. The speed limit was 55 at the time. The top end was ok. The low-end was great. Good "all around" gear, back then. 

Now, 3200 rpm at 70 is too darn high. Too much noise, too much fuel, and with a big block Pontiac, unneeded. I ran a 3.90 gear in a '65 for a while. That car HATED the highway. The top end was 107 mph, at the redline. It would get there really quick, though. I changed out those 3.90s with a 3.36 gear set (the tallest gear set I could run in my 4 series carrier) back in 1990. Changed the car. Now, it loves 70 mph. It feels just about as strong out of the hole (Still can't hook up....tire smoke central), my fuel economy went way up, and my road noise went way down. 

I had another '65 with a 3.23 gear and a 4-speed, and the 3.23 is my FAVORITE gear ratio for these cars. It does everything well: accelerate, cruise, and top end. I drove a '65 with a 2.56 gear. GREAT top end, doggy as hell off the line. Too extreme. A friend had a 2.93 gear in his '67. The car would kick down into 2nd gear (turbo 400) at 85-90 mph. We smoked a 427 '65 Corvette on the highway one day....he was running 4.11's and was done at around 105mph. The '67 would top 140 mph, I'm sure. 

Another friend had a 4.88 geared, dual quad 455 '66. We broke the wheel studs on the rear wheels getting on the freeway one day. He jumped on it, and there we were. The car would lay rubber when you got on it at 65mph, in 4th gear. Scary. The cruising speed was 55 mph. Got about 8mpg at 55! 

My convertible '67 has the stock, 3.36 gearset. I wish it had a 3.23. It is a little busier at speed than I wish it was. I guess I'm getting old...I like running at 75 mph with minimum road noise and fuel consumption. 

Today, there are a lot of options with overdrives, lock-up converters, etc. If you want to modify your GTO and add a 700R4 trans or add a 5 or 6-speed stick, you can run a 3.55 or 4.11 gear and STILL cruise at high speeds. If you're like me and don't want to cut up your original old Goat, you have to choose what gear ratio best suits YOUR needs. 

For this guy, it's 3.23s. 

Jeff


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## Rukee (Feb 8, 2007)

Great post!
My `65 had 3.90s in it when I bought it, and for 13 yrs the car never left town cause the RPMs on the highway were just too high for my comfort level. It was fast, no argument there, and at 35mph I could smoke the tires twice within about 10 feet in a second. Once when I punched the throttle and the second when I snapped off the throttle it would bark the tires again as they slowed down. 

Then a couple of years ago after my wife passed away I really wanted to drive the GTO to some other shows out of town, so I changed out the rear gear to the ratio it had from the factory, the 3.55s. I couldn't believe the difference! It goes down the road like a dream and actually feels faster as each gear seems to have longer legs. 

I think Pontiac did a great job of picking the right ratios right from the factory and I wish I had changed the ratio back years before.


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## blondie67 (Jan 28, 2008)

*Gear Ratios*

Hi,
thanks Jeff for the post...I know there were a lot of gear options for the 67 and whether it had the safettrack or not. At least in my book there seems to be many. Does the rear axle code stamped on the axle tube determine the gear ratio? And if changed out, would it still be there? Ok I know that sounds like a dumb question, but I want to go check on it today. 
Linda


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## Eric Animal (Oct 28, 2007)

My 67 has 2.93 gears....doggy off the line great top end..by todays standards it still feels like it needs another gear (TH400)....I was thinking of a set of 3.73 with a 4spd auto..200r4 can be built to take some torque. It is also an easy swap ....shorter yoke on the drive shaft..and a kit to adapt the his/hers.............Cool Thread


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## geeteeohguy (Feb 2, 2008)

Thanks, folks. Yeah, we've become spoiled with lock-up converters and overdrives. The 200R4 and 700R4 seem to be the swap of choice, provided you run a fairly stock engine. My 3.36 '67 feels like it needs another gear out on the open road. But in the '60s, gas mileage wasn't a concern. 

Linda, yes, the axle code is stamped on the rear end. On your car, it will be a two-letter stamp, on the right side axle tube, facing the rear. the codes begin with a W for standard, open diffs, and a Y for safety-trac (posi) units. Yours should be a WG or a YG for 3.36 if it's the standard ratio. They run WB/YB=2.56, WC/YC=2.78, WD/YD=2.93, WF/YF=3.23, WG/YG=3.36, WH/YH=3.55, WE/YE=3.08, and WK/YK for the 3.90 ratios. 

The only way to tell if the gears were changed is to remove the rear cover and look at the numbers on the gears denoting the number of teeth, or counting the teeth on the ring and the pinion. I have those numbers also if you need them. I think in today's day and age, with the amount of torque and power a Poncho engine has, short gears like the 3.90, etc. are not needed for most drivers. Those gears are better left to high revving, low torque, hi horsepower small block engines. 

Good luck with your hunt. To me, that's the fun of this hobby!

Jeff


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## Ram Air IV (Jul 30, 2007)

Try this site and input values: 

ULTIMATE PONTIAC GTO PICTURE SITE Text Topics article #29


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## Rukee (Feb 8, 2007)

The ratio can also be pretty well estimated by jacking the car up and spinning the rear wheels over. Count the # of drive shaft revolutions needed to make the tire rotate 1 full turn. That`s for a posi rear end, if you have a 1 wheel wonder, only jack one tire off the ground and then spin that 1 wheel 2 full revolutions and count the # of drive shaft revolutions for the gear ratio. My drive shaft turns 3 and just over a half revolutions for every time the tires roll over once for a 3.55 ratio.


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## LOWET (Oct 21, 2007)

geeteeohguy said:


> Hi. I'm posting a new thread because I didn't want to hijack another thread that this subject came up on: Gear ratios. I was bragging about my "racing" days, and gear ratios were mentioned. The following is some information that I have learned over the years, and the following opinions on gear choice are my opinions and nothing else. I am no engineer. I've run GTO's over the years with ratio's from 2.56:1 to 4.56:1. Stock early GTO's with stickshift usually came through with 3.55 gears, and aut0 cars had 3.36 gears standard. The 3.55 (4-Series) carrier could accomodate gears from 4.88 or so down to 3.36. The 3 series carriers could accomodate gears from 3.23 down to 2.51. I found that "back in the day", with cheap gas and road noise a fact of life, the 3.55 gears were okay.....the '66 tended to be running about 3200 rpm at 70mph....right in the power band. The speed limit was 55 at the time.Top end was ok. Low end was great. Good "all around" gear, back then. Now, 3200 rpm at 70 is too darn high. Too much noise, too much fuel, and with a big block Pontiac, uneeded. I ran a 3.90 gear in a '65 for a while. That car HATED the hiway. Top end was 107 mph, at redline. It would get there really quick, though. I changed out those 3.90's with a 3.36 gearset (the tallest gearset I could run in my 4 series carrier) back in 1990. Changed the car. Now, it loves 70 mph. It feels just about as strong out of the hole (Still can't hook up....tire smoke central), my fuel economy went way up, and my road noise went way down. I had another '65 with a 3.23 gear and a 4-speed, and the 3.23 is my FAVORITE gear ratio for these cars. It does everything well: accellerate, cruise, and top end. I drove a '65 with a 2.56 gear. GREAT top end, doggy as hell off the line. Too extreme. A friend had a 2.93 gear in his '67. The car would kick down into 2nd gear (turbo 400) at 85-90 mph. We smoked a 427 '65 Corvette on the hiway one day....he was running 4.11's and was done at around 105mph. The '67 would top 140 mph, I'm sure. Another friend had a 4.88 geared, dual quad 455 '66. We broke the wheel studs on the rear wheels getting on the freeway one day. He jumped on it, and there we were. The car would lay rubber when you got on it at 65mph., in 4th gear. Scary. cruising speed was 55 mph. Got about 8mpg at 55! My convertible '67 has the stock, 3.36 gearset. I wish it had a 3.23. It is a little busier at speed than I wish it was. I guess I'm getting old...I like running at 75 mph with minimum road noise and fuel consumption. Today, there's a lot of options with overdrives, lock-up converters, etc. If you want to modify your GTO and add a 700R4 trans, or add a 5 or 6 speed stick, you can run a 3.55 or 4.11 gear and STILL cruise at high speeds. If you're like me, and don't want to cut up your original old Goat, you have to choose what gear ratio best suits YOUR needs. For this guy, it's 3.23's.
> Jeff


I had 513s in my 67 Camaro. I could get it to wheelie in 1st and 2nd


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## VettenGoat (Jun 19, 2007)

Thanks guys, I've been having the same inner dilemma. The 65 originally had 3:90s like Rukees, but they are long gone several owners ago and now it has a wrong 1971 rear in it with 3:23s. So I am still looking for a 65 rear and thinking about what ratio to use with the 421. Geetoguy is right, we're not kids anymore and gas isn't .35 a gallon so 3:90s are out. I'm tossing up whether to go 3:55s or 3;73s. Anyone running 3:73s? Thoughts?
Mike


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## blondie67 (Jan 28, 2008)

*The reason I asked....*

The reason I asked this question is that the previous owner I think put 4.11 (is this right?)gears in it and it feels like it needs 2-3 more gears on the freeway. It's great around town, but I want to change it back to stock so I can cruise this summer.
Thanks for all your input!
Linda


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## Eric Animal (Oct 28, 2007)

4.10 gears are too stiff for cruising....about 3000 rpm's to do 55. You will shorten your engine life and not enjoy the ride.....3.55 is probably a good ratio to use "Ask your Doctor if 4.10's are right for you".......if I never hear that commercial phrase again ......................


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## geeteeohguy (Feb 2, 2008)

VettenGoat: In my opinion, especially with a 421, I would get a "year correct" rear end for your car and run a 3.23 gear or a 3.36 gear. A 3.55 gear with a 421 would sure be great around town, but you'll be wound out on the freeway, looking at shorter engine life, higher engine temps, more road noise, and less fuel economy. The 421 has enough torque to run a really long legged gear like a 2.93 or a 3.08 and still not be able to hook up! I would suggest going for a ride or driving a 3.73 or 3.55 geared car and see how you like it. With me, it was great when I was 19, but now, I like to get in the car and GO SOMEWHERE!!! As for 5.13 gears, Yeah, I saw a guy in a white '67 Camaro one day waaay back when pull the front wheels up about 18 inches out af a stoplight on San Leandro Blvd. Needless to say, I didn't even race THAT Chevy!!!!
Jeff


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## Rukee (Feb 8, 2007)

The size of the engine won`t change the RPMs. I have 3.55`s with a 4-speed and it goes down the interstate with ease. I even raced a Bemmer looking thing up to about 125 and it was still pulling away strong. I drive the car all over the state and it cruzz`s awesome down the highway. A lower # ratio would get better millage, but who drives their classic GTO for gas millage??


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## geeteeohguy (Feb 2, 2008)

You're right about the RPM's, Rukee. But a 421 rev's lower than a 389, and makes more power at lower RPM's. While a 3.55 is the standard gear for a 389 equipped stickshift 3400 pound GTO, the usual gearset for a big Pontiac with a 421 and stickshift seems to be 3.42 or 3.36. 3.55 was considered the best "all-around gear" in the GTO back then....... Like you, I had 3.90's out back until I went as long legged as I could: 3.36's. I have no regrets!!!!!!


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## ppurfield001 (Jan 21, 2008)

Rukee said:


> The size of the engine won`t change the RPMs. I have 3.55`s with a 4-speed and it goes down the interstate with ease. I even raced a Bemmer looking thing up to about 125 and it was still pulling away strong. I drive the car all over the state and it cruzz`s awesome down the highway. A lower # ratio would get better millage, but who drives their classic GTO for gas millage??


I'm trying to figure out this gear ratio thing, Rukee. If I am going 70 mph on the highway, my 400 cubic inch engine is at about 3200 RPMs. Is that similar to your story above and, if you can venture a guess, what kind of gears am I running?


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## Rukee (Feb 8, 2007)

Your best guess to figure it out would be to do like I suggested above with a jack. You can get very close to what the real ratio is.


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## 05GTO (Oct 6, 2004)

ppurfield001 said:


> I'm trying to figure out this gear ratio thing, Rukee. If I am going 70 mph on the highway, my 400 cubic inch engine is at about 3200 RPMs. Is that similar to your story above and, if you can venture a guess, what kind of gears am I running?


Pull the diff cover and count the teeth on the ring and pinion, then divide the # of ring teeth by the number of pinion teeth. 

Another way is by using Rukee's method and turn the tire 10 times and if the drive shaft turns 39 times the ratio would be a 3.90.


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## Rukee (Feb 8, 2007)

10 tire revolutions is too many, between counting the tire and the driveshaft it` too easy to lose count. 
That`s what the ratio is though, how many times the driveshaft turns for evey one complete turn of the tires.


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## ppurfield001 (Jan 21, 2008)

Rukee said:


> 10 tire revolutions is too many, between counting the tire and the driveshaft it` too easy to lose count.
> That`s what the ratio is though, how many times the driveshaft turns for evey one complete turn of the tires.


Thank you Rukee and Randy.


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## LOWET (Oct 21, 2007)

VettenGoat said:


> Thanks guys, I've been having the same inner dilemma. The 65 originally had 3:90s like Rukees, but they are long gone several owners ago and now it has a wrong 1971 rear in it with 3:23s. So I am still looking for a 65 rear and thinking about what ratio to use with the 421. Geetoguy is right, we're not kids anymore and gas isn't .35 a gallon so 3:90s are out. I'm tossing up whether to go 3:55s or 3;73s. Anyone running 3:73s? Thoughts?
> Mike


The 3:55s should work well with a 421. they made a lot of torque


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## Eric Animal (Oct 28, 2007)

TryRandy's Ring & Pinion click on the calculator section and enter values.....lot's of fun and info. Eric


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## Priest (Feb 2, 2008)

When my dads GTO was a monster,
It had a *4.88* rear end arty:


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## Rukee (Feb 8, 2007)

Priest said:


> When my dads GTO was a monster,
> It had a *4.88* rear end arty:


You mean a 3.08? Or a 3.90? I`ve never seen anything higher then a 4.56 ratio fit a std GTO rear end, and that thing would be screaming just running around in town with 4.88s, it would never be able to go down the highway without an overdrive unit unless it had just incredibly huge tall tires or somethin. Not to mention no-one I can find offers a 4.88.


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## Priest (Feb 2, 2008)

Yup, Im sure my dad had a 4.88 haha

But yes, he did say it was a bad idea since the RPM red-lined and drove him crazy.
Hence why it was removed quickly.

BTW what does "std" stand for...referring to a GTO rearends lol


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## Rukee (Feb 8, 2007)

std = standard
I`ve never seen a 4.88 fit a standard GTO rear end housing.


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## geeteeohguy (Feb 2, 2008)

The only 4.88 geared GTO I experienced personally was my friend's '66. He put the gears in a 12 bolt unit we got out of a red 1970 455 4 spd GTO that we paid $175 for. (the ign. points had closed up). He tweaked the dwell and drove it home. We proceeded to strip the car and use the parts to re-do his '66. Back then (1980) we had NO idea that the '70 was extremely rare (something like 108 455HO 4 spd cars made total), or we wouldn't have parted it out. It was red with a parchment interior, and was pretty clean. I have never seen anything steeper than a 4.11 gear in a stock, early A body 10 bolt housing/carrier, though the Ram Air 1 in 1967 had a 4.33 gear standard in it's 10 bolt rear end.
Jeff


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## Priest (Feb 2, 2008)

Sorry all, had a brain-fart resulting in the unrocognization of 'std'.

Any way that is because it wasnt in a standard GTO rear end.
The rear end was probably out of an A-body that could bolt right in.


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## 70455goat (Nov 5, 2007)

I am very interested in finding out what my rear end is.

UltimateGTO.com says my 70 (455) with a 12 bolt should have 3.07 (std) or 3.31 (opt). My GTO is completely all original and all I know is that it is pretty low geared. When I get on the freeway, it seems like I am still in second gear when I get up to 55-60 MPH. Correct me if I'm wrong, but 3.31 is not very low gears are they?

I couldn't find my source, but I remember reading info about a tag or something I should be able to find on the outside of my rear end. Does anyone know anything about it?

Dale,


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## Rukee (Feb 8, 2007)

The cover on the back may have a tag. If you remove the cover there should be a # on the outside edge of the ring gear that will give the ratio. Or you could count the # of teeth in both the ring gear and the pinion and divide the pinion by the ring gear.
Or like I suggested above, jack up the rear end off the ground, turn the tires over one full revolution (if it`s a posi unit) and count the # of times the drive shaft turns over and that`s your ratio. If you have a 3.31 then the drive shaft will turn over 3 and almost a half revolutions for every time the tire turn over once.


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## ppurfield001 (Jan 21, 2008)

Rukee said:


> The cover on the back may have a tag. If you remove the cover there should be a # on the outside edge of the ring gear that will give the ratio. Or you could count the # of teeth in both the ring gear and the pinion and divide the pinion by the ring gear.
> Or like I suggested above, jack up the rear end off the ground, turn the tires over one full revolution (if it`s a posi unit) and count the # of times the drive shaft turns over and that`s your ratio. If you have a 3.31 then the drive shaft will turn over 3 and almost a half revolutions for every time the tire turn over once.


Rukee's simple methodology above worked for me in determining that I had a 3.90 gear ratio.


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## Rukee (Feb 8, 2007)

ppurfield001 said:


> Rukee's simple methodology above worked for me in determining that I had a 3.90 gear ratio.


I just replaced a 3.90 with a set of 3.55s and couldn`t be happier. The car feels alot faster too as it seems to have longer legs between each gear and goes down the highway excellent. :cheers


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## ppurfield001 (Jan 21, 2008)

Rukee said:


> I just replaced a 3.90 with a set of 3.55s and couldn`t be happier. The car feels alot faster too as it seems to have longer legs between each gear and goes down the highway excellent. :cheers


Point taken -- with the close ratio four-speed and the 3.90 gear ratio, the time between shifts on my goat is very short. Any idea how much it would cost me to go to 3.55 gears from 3.90 gears if I got a mechanic to do the changeover for me? Thanks.:cheers


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## Rukee (Feb 8, 2007)

I would expect to pay about $300-400 with parts and labor included depending on which set of gears you go with. You can pick up brand new gears from $227. I bought the Richmans myself, though the ones I bought didn`t say "Richmond Gear is not recommended for quiet applications." like these do, mine run quiet.
Auto Parts: YG GM8.2-355 - High performance Yukon Ring & Pinion gear set for GM 8.2 in a 3.55 ratio. Yukon exclusively uses 8620 steel in all their Ring & Pinion sets for high strength and long life. They use the latest designs and manufacturing tech
Auto Parts: RG 49-0015 - Richmond Gear ring & pinion gear set for GM 8.2 in 3.55 ratio. Richmond Gear has long been a staple in the performance gear market place with products geared towards the racing market. Their gears are made strong to withstand


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## ppurfield001 (Jan 21, 2008)

Rukee said:


> I would expect to pay about $300-400 with parts and labor included depending on which set of gears you go with. You can pick up brand new gears from $227. I bought the Richmans myself, though the ones I bought didn`t say "Richmond Gear is not recommended for quiet applications." like these do, mine run quiet.
> Auto Parts: YG GM8.2-355 - High performance Yukon Ring & Pinion gear set for GM 8.2 in a 3.55 ratio. Yukon exclusively uses 8620 steel in all their Ring & Pinion sets for high strength and long life. They use the latest designs and manufacturing tech
> Auto Parts: RG 49-0015 - Richmond Gear ring & pinion gear set for GM 8.2 in 3.55 ratio. Richmond Gear has long been a staple in the performance gear market place with products geared towards the racing market. Their gears are made strong to withstand





Thank you Rukee. I will investigate the parts supplier described above. By the way, in determining my current gear ratio according to your methodology, I also confirmed that my goat has posi-traction.


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## CJD (Feb 2, 2008)

Hi, I've got a 68 goat that I bought in Mid-Michigan and I am trying to find out what gear is in it. I read your response and I went out with a wire brush and I could not find the W/Y designation. Is it close to the pig or more outboard?

Thanks,

CJD


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## Rukee (Feb 8, 2007)

CJD said:


> Hi, I've got a 68 goat that I bought in Mid-Michigan and I am trying to find out what gear is in it. I read your response and I went out with a wire brush and I could not find the W/Y designation. Is it close to the pig or more outboard?
> 
> Thanks,
> 
> CJD


Welcome to the forums.
As described above, to find your rear end ratio jack up the rear off the ground and rotate the tires one full revolution(for a posi unit), count the # of times the drive shaft turns to make the tires roll over one full turn. If only one tire rolls(open rear end) then block the one wheel and turn the one tire over two full revolutions and again count the # of drive shaft turns for your ratio. If you had a 3.90 gear the drive shaft will turn over almost 4 full revolutions (3.9 times to be exact), if you had a 2.73 ratio then the drive shaft will turn 2 and almost three quarters revolutions for every time the tires turn over once. It`s a very effective way to find your ratio.


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## rick3452 (Jun 14, 2008)

Having the 390's taken out and the 323's put in my 66 next Tuesday.Looking forward after almost forty years of driving this car to cruising the highway. Thanks for all the great info!!! Rick


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## geeteeohguy (Feb 2, 2008)

Rick: You're gonna kick yourself for not putting in the 3:23's 30 years earlier!! You'll love 'em! Good luck with the swap!
Jeff


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## Rukee (Feb 8, 2007)

I know going from 3.90s to 3.55 was a world of difference in my `65! I just swapped out the rear gears in a `71 Challenger 440 six pack car from 4.10s to 3.54s and that guy is sooo freakin happy he almost kissed me.


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## rick3452 (Jun 14, 2008)

Thanks Jeff....


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## rick3452 (Jun 14, 2008)

OK I don't get it..... I pick up my 66 yesterday, I dropped it off on Tuesday, a few hrs later I got a call from the shop saying that I did not have 390's but 355's instead. I was having 323's installed. He said that there would not be a big difference, but I said do it anyway. The car ran 3500 @ 65 MPH on the way to the shop, and on the way home after the change to the 323's it ran 3500 @ 65 mph. No change at all!! I can not figure it out, what are you guys revving at 65, with 323's??
$789.00 and no difference.....Thanks Rick


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## Rukee (Feb 8, 2007)

I`m running about 2800rpm @ 65 with 15" tires on the back and 3.55 gears, manual tranny.
Remember too, you did not change the tranny speedo gear, so more then likely you were driving faster then the 65 indicated on the speedo.(or you use to drive slower then 65 when the speedo said 65) Without changeing the speedo gear it will show the same speed and RPMs you were running at before as the change you made was after the speedo gear, in order for the speedometer to be acurate you need to put the right speedo gear in the tranny too.
Here is a gear ratio calculator, if you messure your tire size you can see what speed you should be running at what rpm.
Differential Gear Ratio Calculator
To verrify your gear ratio you could jack up the car and spin the wheels over one revolution and count the # of times the drive shaft turns, it should be 3 and about a quarter turns for every time the tires turn over once.


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## rick3452 (Jun 14, 2008)

Hey Rukee, How would I change the speedo gear, and where to purchase? I was also listening to the motor at 65 seemed like 3500 rpm's to me.???


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## Rukee (Feb 8, 2007)

The gear is on the end of a holder that goes into the tranny at the tail housing. The speedo cable screws into it. Remove the cable, then remove the attaching nut (or bolt) that secures the gear holder to the tranny. The holder unit will pull straight out, though it may be tough to get out, try twisting or turning it to get it to let go. Once out there will be a removable plastic gear on the end, checking with your GM dealer and giving them your tire size and rear axle ratio they should be able to fix you up with a gear that will be closer then you have now. If the dealer can`t help you, check with some tranny shops in the area. You need an RPM gauge to be sure what you`re running at.


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## rick3452 (Jun 14, 2008)

Great...Thank You..


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## 68greengoat (Sep 15, 2005)

Check this out. They have a bunch on e-bay and also tell you what to use for what gear ratio.

eBay Motors: NOS 67 68 69 70 71 72 GTO Camaro 442 GS Chevelle 3.23 (item 310071232176 end time Aug-03-08 16:23:53 PDT)


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## rick3452 (Jun 14, 2008)

Green Goat......Thanks much!!


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## Scott Gelande (Oct 3, 2008)

I am looking for a set of 3:23 gears for my 66 tempest. Can anyone tell me where to go to buy these?


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## ppurfield001 (Jan 21, 2008)

Rukee said:


> The gear is on the end of a holder that goes into the tranny at the tail housing. The speedo cable screws into it. Remove the cable, then remove the attaching nut (or bolt) that secures the gear holder to the tranny. The holder unit will pull straight out, though it may be tough to get out, try twisting or turning it to get it to let go. Once out there will be a removable plastic gear on the end, checking with your GM dealer and giving them your tire size and rear axle ratio they should be able to fix you up with a gear that will be closer then you have now. If the dealer can`t help you, check with some tranny shops in the area. You need an RPM gauge to be sure what you`re running at.


Rukee, thanks. I am going to get my gear ratio changed from the current 3:90 to one to 3:55 or 3:23 to one. Thanks to you, I will get the speedometer gear changed so that my MPH and RPM readings remain accurate. Thanks again for the good advice.


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## teamwoody72 (May 23, 2008)

where can i get the kit to adapt to the his and hers


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## Rukee (Feb 8, 2007)

teamwoody72 said:


> where can i get the kit to adapt to the his and hers


Kit? for what? ring and pinion kit? speedo gear kit?


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## geeteeohguy (Feb 2, 2008)

WTF??? Maybe a shifter kit? His/Hers is usually slang for Hurst DualGate.....


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## teamwoody72 (May 23, 2008)

sorry my post got cut off, i was wondering where to get a kit for the 200r4 trans to adapt the his and hers shifter that one of the previous replies mentioned in this thread..


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## Chris Holabaugh (Jan 18, 2009)

Your engine can be a factor in your gear ratio. My current 65 has 4.10's and they good match for engine I have if wanted to race it, but I have decided not to put on the track. The car has a 12 bolt so I am go to change either to a 3.42 or 3.55 so that I can cruise with out the high an rpm an less noise.


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## NC_Mike (Jun 2, 2009)

*Gear ratios with a 2 speed Trans in a 64*

Hey everybody!! I'm new to the forum and wanted to add a question to this discussion. I have a 64 with Tri-Power and a 2 speed tranny. Did the GTO only come with a powerglide or somebody told me I may have a Super Turbine 400. So the reason for the question is I have read the posts and I want to know if the transmission I have will affect the rear end gearing? I run my car on the highway just to get around town and it is reving about 3500 when I am keeping up with traffic. My speedo hasn't worked since I got the car, but I just installed an MSD so I know that the tach is correct. I am having going to check to see what I have now in the car. It seems like most guys like the mid 3's for gearing, will that still give me good performance with my 2 speed and not blow my engine on I-540??? Thanks for any help, I'll post some pics soon


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## 05GTO (Oct 6, 2004)

NC_Mike said:


> Did the GTO only come with a powerglide or somebody told me I may have a Super Turbine 400.


Welcome to the forum, your transmission should be a 2-speed Super Turbine 300, the 400 was a 3 speed automatic used in 64 with Cadillac and Buick and later (65-67) used with Pontiac, Olds and Chevy in the larger B-body cars.


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## geeteeohguy (Feb 2, 2008)

The Super Turbine 300 is also a heavier duty unit than the standard Powerglide. Bulletproof trans, if not too inspiring. It won't affect your final drive ratio. Like all other standard and automatic non-overdrive trannies, it has a 1:1 final drive ratio in 2nd (top) gear. Your car should have come with a 3.23 gear standard. 3500 rpm at 70-75 mph sounds like it has 3.55's in it. You can easily verify it.


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## NC_Mike (Jun 2, 2009)

So the car does have a 3.55, I want to lower the gear so I can drive on the highway and run my aftermarket air. So the big question where can I get a lower gear? The 8.2" rear end is difficult to find gears. I want to run a 3.08 so I can stay cool and still go down the highway. Where could I find one? The other thought is to switch to a 8.5" rear end, obviously save all the old parts. Would a 8.5" rear end have any issues (drive shaft, suspension, anything?). Has anybody done this and how did that go?


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## Silver69GTO (May 25, 2009)

I just read through this post and I don't recall anyone mentioning how tire diameter effects the rear gear ratio.
If you're running a wheel and tire combo that's the same overall diameter as what came stock from the factory, then 3.55's or higher (numerically) might be too much on the freeway.
My '69 GTO has the stock 350HP/400 with a TH400 trans and 3.55's, but I run a set of 15X8 Drag Lites with 255/60-15's. If I remember right (the car has been torn down for paint), the tach read 2200RPM at 60MPH.
For me, that's acceptable.
But then again, the car I owned before this GTO was a '69 Dart with a built 340 and 4.88's. That thing screamed at 60MPH.


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## geeteeohguy (Feb 2, 2008)

Good point, Silver. Going from a stock 25 inch tall tire to a 28 or 29 incher will make a world of difference. That's why 4x4 guys have to gear lower when going with the tall tires....to keep the revs in the powerband. 3.55's with a tall tire sounds like it's a good combo for you.....2200 at 60 puts you right at the beginning of your powerband.....right where you wanna be!


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## NC_Mike (Jun 2, 2009)

I found this website to calculate tire diameter and gear ratios vs. rpm's. I first used it to make sure that my tach was correct after I added the MSD box, and it was right. If my car didn't have the original spinner hubcaps I would have just replaced the wheels, but I really like that old school look with the spinners and the red stripe tires. 

Technical Information for diagnosing drive line problems, Installation and repair of differentials and setup specifications.


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## Silver69GTO (May 25, 2009)

Well, according to the calculator, my GTO should be turning 2800RPM at 60MPH with 255/60-15s and 3.55 gears.
Either my memory is wrong or I am mistaken on which gear ratio is in the rear end.
Once I get the car back on the road (it's getting paint), I'll have to re-test.


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## 646904GTO (Feb 10, 2008)

geeteeohguy said:


> The only 4.88 geared GTO I experienced personally was my friend's '66. He put the gears in a 12 bolt unit we got out of a red 1970 455 4 spd GTO that we paid $175 for. (the ign. points had closed up). He tweaked the dwell and drove it home. We proceeded to strip the car and use the parts to re-do his '66. Back then (1980) we had NO idea that the '70 was extremely rare (something like 108 455HO 4 spd cars made total), or we wouldn't have parted it out. It was red with a parchment interior, and was pretty clean. I have never seen anything steeper than a 4.11 gear in a stock, early A body 10 bolt housing/carrier, though the Ram Air 1 in 1967 had a 4.33 gear standard in it's 10 bolt rear end.
> Jeff


Years ago I had a 65 with the 'dealer optioned' 4:33 gear. She went only 95mph @5000rpm (if memory serves me right), but you couldn't get the dollar off the dash!. The car is since long gone but the gears are in a cabinet in my garage today


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## xconcepts (Jan 4, 2009)

I've got a question about the two rear ends I have currently for the 66. I have the original 3.55 rear end stored away right now and it was replaced, not by me, with a 2.56 rear end for another year, don't know which year or model. I'm wanting to go to 3.23 so should I use the original 66 rear end or change out the current rear end that is on her?


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## xconcepts (Jan 4, 2009)

bump for help.


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## geeteeohguy (Feb 2, 2008)

CORRECTION: On my first post in this thread, I stated that a "3-series carrier" could accomodate "2.51--3.23 gears". This turned out to be wrong! A 3 series carrier will work with 2.93 thru 3.23 gears. A TWO series carrier is used for the really long legged ratios: 2.29 (big cars) 2.56 (Tempest) thru 2.73 ratios. The reason you can't put a 3.23 ring and pinion in a 4 series, etc. has to do with carrier fitment. The really short rears (4 series, have a thick ring gear and smaller pinion. The highway star rear ends have a huge pinion gear and a thin ring gear. You can't readily change gears in incompatible carriers. Apologies for the confusion, but you learn something every day!!
Jeff


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## HoJo GTO (Sep 21, 2009)

I have a chevy 12 bolt rear housing that I plant build for my 67' GTO. Not being able to pick a gear is partly why it's not in the car! Do you have a gear recommendation for my chevy 12 bolt? 3.31 perhaps? The car has a turbo 400 automatic tranny but I have not ruled out a "built" 200R4 tranny in the future. Thanks!

Hollie


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## geeteeohguy (Feb 2, 2008)

A 3.31 gear would be an excellent choice for your '67 GTO, Hollie. Good accelleration, and good cruising on the freeway, as well. The stock, standard gear ratio for a '67 GTO with the Turbo 400 trans was a 3.36. You're right there. Good luck.


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## Gran Turismo (Jan 12, 2010)

Hi.
Can anybody clarify what the numbers "40 13 GM 965 XO" on the rear diff mean? in relation to the back axle ratio. Maybe just factory part stamps? I cant find the letters on either axle tubes work out the ratio. Thanks.


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## 68gtohawk8369 (Oct 26, 2009)

*331gear ??*

I know what its like to have a good gear for "out of the whole performance" at this point in my life Im looking for the best of both worlds I have come across a 1969 chevelle posi with 331 gear if 323's are good im thinking 331 would be acceptable the problem is I cant go pick it up until Sunday I hope it will still be availabe I still havnt received any answers on what I will be looking at as far as installing this in my car a 1968 GTO any input would be appreciated thanks


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## geeteeohguy (Feb 2, 2008)

68gtohawk: it is a straight, bolt-in deal. No mods needed. 3.31 is a great ratio for all-purpose driving. You may want to change out the rubber trailing arm bushings and rear housing bushings with new parts. If the rear bearings rotate smoothly and are not leaking oil past the seals, I would leave them alone. Ditto the pinion seal. If it ain't broke, don't fix it. Be sure to use limited slip additive with the gear oil, or you'll damage it!


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## par4n1 (Jan 28, 2010)

Well I guess what I thought was a rare though unimpressive 3.36 was a very standard gear. Oh well hard to learn it all in two weeks.


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## 69Judge (Feb 21, 2010)

Hey guys my rears are Mickey Thompson drag radials 295 65 15, what do you think would be the best ratios for that?


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## geeteeohguy (Feb 2, 2008)

If you're refering to stock rear ends/ratios, the best ratio for quarter mile would be 4.33, and the best ratio for high speed cruising would be 2.56. Most real-world conditions call for something in between.


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## 69Judge (Feb 21, 2010)

they are currently 4.10, looking for more of a cruising/street ratio


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## Cardinal70 (Jan 31, 2010)

Thanks for the post, OP. I haven't had the chance to drive my '70 yet, and I was worried that it would be too lazy wth the 3.23 gears. Sounds like it should be OK though.


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## BCsGTO (May 17, 2010)

Ok guys I found a broken rear wheel stud on my goat. Is it possible to replace it without pulling the axle?


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## geeteeohguy (Feb 2, 2008)

Yes. But be careful not to bend the flange when you're knocking the old stud out. Use penetrating oil and common sense. Pull the new one in with big washers or oversize nuts under the lug nut, and use anti-sieze.


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## Unclesams (Jun 5, 2009)

I own a 1968 GTO HO convertible of which there is VERY LITTLE LEFT. The car came from the factory with 4.33 gears and a close ratio 4 spd Muncie, no disc brakes, no hideaways, in Aegena blue/black/black. Like a drag car convertible from the factory. Sadly the rear and the entire drive train are long gone!


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## 67lemans (Oct 30, 2009)

I appologize if it's in here and I can't figure it out, but, what would be the highest ratio that would bolt into a 2.56 rear (which is what I have). and yes it performs just as described above. Thanks.


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## geeteeohguy (Feb 2, 2008)

The highest ratio would be a 2.78 gearset. Shared only with the 2.56 gearset on the 2-series carrier.


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## roy (Jun 1, 2010)

*Other choices*

I was running a 3 speed auto in my 64, with 3:73's which was great for out of the hole but as we all know, 70mph @ 3600rpm just gets to be to much after about 50 miles!
I didn;t want to cut the tunnel or pull the trans. for that matter. I'd hung out with some serious drag racers who wanted low gears but able to drive to the strip too & most of them were running a Gear Vendor unit behind their stock 3 speed autos & even factory 4 speed manuals.
I don;t know if you know how a gear vendor unit works, but briefly, it litteraly gives you a gear between each of your stock trans gears so, a 3 speed becomes a 6 speed & so on
And, those "extra" gears are availalbe anytime at any speed or you can leave the control in "auto" which lets your trans do its normal 1,2,3 shifts & then goes into an O/D gear (.67 or .70) like any O/D trans
Flip the switch to manual(mounted on your shifter or dash or foot switch) & go to your redline in 1st, hit the button & go into 1st over, 2nd to 2nd over & so on
The beauty of the GV unit to is you only drop like 250-350rpm between shifts so your motor is always in its sweet spot! Unlike a stock 3 speed where the shift from 1st to 2nd you loose what? 600-9000rpm & the motor has to lug its way up to its ideal RPM range again!
I;m running one now, with 3:75;s & in 6th or O/D whatever you wanna call it i'm turning 2100rpm @ 70mph.
Plus, the "over" gears are just perfect when say, 2nd is to high, and/or 3rd is to low. You always have a perfect gear for any situation & shifting through 6 changes up & downshifting is just to much fun never mind you can knock seconds off your 1/4 mile times or in my case, on a 2.5 mile course i knocked a full 7.5 seconds off my track time.
By the way, their guranteed to handle 1200HP!
Worth a look at the Gear Vendor site


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## 66tempestGT (Nov 28, 2009)

my dumptruck has that too.


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## mshidner (Apr 11, 2009)

Hello, anybody running a five or six speed in their 67 to 70? I just purchased a 67 with 400 engine and a Richmond five speed. The rear is a 2.73 or close to that. The car really needs a bump in the low end off the line. In top gear at 65 it is turning about 1850 rpm. I would assume I have the wrong carrier to bump up to a 3.55. If so what is needed to convert to the proper carrier and what might the cost be? Is there any calulator out there that would tell a person what kind of gas mileage one might expect when changing gear ratios?


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## Eric Animal (Oct 28, 2007)

Don't know what yourbudget is but.....check out MOSER REARS !!


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## AMT1379 (May 11, 2010)

I have 4:10s now in a 12-bolt that seems to be in good shape (so far). I do want want to change to a 3:55 or 3:08 (Trying to get as close to the original 3:36 as possible). Do I need to get a 3 Series carrier? Is it best to buy a new three series carrier and gear set or to try and swap the whole rear? Baby on the way, so I'm looking for the most fiscally responsible option, on the other hand, I wouldn't know what to look for I was trying to arrange a swap.


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## AMT1379 (May 11, 2010)

I've done some more reading & research, but I want to verify I'm on the right track if I can. Since I have the 4.10s now, if I want to get closer to the original 3.36 I'll need to get a new 3-series carrier and a new gear set. Looking at Randy's Rack & Pinion it looks like the closest I can get to 3.36 with the 12-bolt that's in the car now is a 3.55. Cost for a new 3-series carrier and gear set plus misc parts is ~$400, plus labor for install I'm look at ~$600 or more?

Assuming I'm not way off base looks like it's back roads and 4.10s for another couple of years.


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## geeteeohguy (Feb 2, 2008)

Those prices sound cheap, to me. I don't know from 12 bolts, but with a 10 bolt, you need the 4 series carrier, which will work with 3.36 up thru 4.33 gears. The 3 series carrier in a TEN bolt will run with 2.93---3.23 gears. I understand a 3.23 ten bolt posi recently sold for $300 at Norwalk....you might try Craigslist, etc. and do a complete swap. I swapped my pegleg stock 3.36 entire rear end for a 2.56 posi recently....because the 2.56 was gratis. I love it out here where it's flat and the roads are long. 2450 RPM at 75mph, getting over 19 mpg. in a '67 GTO ragtop.....


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## pon64gto (Sep 13, 2010)

I'm new to the forum and I would like to ask a question about the '64 GTO's. I'm currently running a 3.90 posi rear end and I want change it out for a 3.36 gear. On ebay Drivetrain parts of Las Vegas is offering two different models of the GM 8.2 10 bolt ring and pinion. Their offering the GM 8.2 10 bolt 3.36 (Yukon Gear) for $210 and they also offer the GM BOP (Buick, Olds, Pontiac) 8.2 10 bolt 3.36 (Yukon Gear) for $310. My question is: Do I need the GM BOP 8.2 gear or can I use the normal GM 8.2 gear? Both will be 3.36 ratio. I'm confused on which one is right for my car.
Thanks in advance, Mike


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## geeteeohguy (Feb 2, 2008)

Mike, tell them what you have and they should be able to help you. The 3.36 gear will work fine with your present 4 series (low gear ratio) carrier. You will find that they will transform your high revving, fuel guzzling car into a really nice all around driver: good power in all the gears, much better fuel mileage, and nice cruising at 70mph (instead of 55!). My bet is you need the BOP specific one (the most expensive one, of course!)


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## KarLvr (Oct 28, 2010)

*Transmission interchange*

I noticed one of the threads mentioned using a 200r or a 700r4 in a GTO. I have a 65 model with a 389. As I have checked with the transmission rebuild shop owned by a friend, he states that the 700r4 , 4l60e and etc cannot be used as they will not bolt to the engine. I thought about using an adapter but have not found one that will work and then there is the issue of torque converter align pilot not being deep enough in the flywheel. Anyone ever put a 4l60E with a early 389?


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## onetwomany (Apr 22, 2011)

Cant you fab up your own adapter plate. I did it years ago in my shop. I bet the guys in my shop that I could install a BOP trans in a small block Chevy Impala.
The bet was I had to start on Friday after work and drive it to work on Monday. 
Hint: I won the bet. And yes the converter has to be shimmed the same ammount as the adapter plate. Dont ever let people tell you you cant do something. Go for it!


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## Thumpin455 (Feb 17, 2010)

I got an adapter to bolt a 700R4 to my 455 and it has the pilot bushing for the crank to converter. Summit has it and they run less than $100 700R4 - Pontiac - Bellhousing Adapters - Drivetrain - SummitRacing.com. I also have 2004R behind my engines and they work pretty well with a decent rebuild and a shift kit. They dont live as long behind a 455 as they would a 350, but they live no problem if you arent beating on it often.

I ran the 2004R with 2.93 gears in my 70, it was 4100lbsm stock converter stall and still ran 13.50s, that is moving quite a bit of mass. I will see how long a 700R4 lives behind a 500hp/tq 455 this summer.


In reply to the to the start of the thread... I like the 2.41-2.56-2.73-2.93-3.08-3.23 gears too. I dont like to go over 3.42 with my Pontiacs.


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## regguy1 (Aug 5, 2010)

I'm a transmission rebuilder for 45 years.....

FYI: OD ratios in 4L60 (700R4) and 2004R are .75 to 1.00 they will reduce crusing RPM by 25%
2004R has a "universal" bellhousing bolt pattern, it will bolt to BOP (Buick / Olds / Pontiac) and Chevy engines.

Photo is of one I rebuilt for a classic truck conversion, you can see the universal bolt pattern

*Watch my garage tour video, It's contest entry...help me win a prize 
Most views on you tube by 04/15/2012 wins* send it to everyone you can :cheers






Thanks


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## rickm (Feb 8, 2012)

hi, the axle code will still be there but that doesnt mean thats what you got.the best way to determine what ratio you have is what rukee posted. rickm.


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## jigaway (Jul 2, 2011)

Forgive me if asking a redundant question. I don't particularly like the current gears in my 71. they are 3:31s. (I had them taken out, counted and verified).

I am "really in to" the accelerator at 55 and it just seems like the engine is really screaming. I find myself worrying about blowing the engine or wearing it out. Maybe that is just the way it is.

The car is a YS 400/TH400 auto trans bored 0.3. Some sort of high performance heads.
I am running 265/60/15s on the rear. From some of the calculators on line, I am doing roughly 2500 RPMs @ 55. If I put a 3.08 gear in to the calculator, it only drops the RPMs about 175 less. Doesn't seem like much. Is it worth the money to put in the 3.08s? 

I am wondering if there is more to it than just the numbers. :confused

Thanks for any wisdom. 

Dan


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## Instg8ter (Sep 28, 2010)

you will notice the difference...if you like highway driving and better gas mileage go to a 2:7X posi, i have a 2:56 open behind the 463 and i was getting double digit mileage and it would still disembowel the tires up to a 20 roll with a stomp of the foot. Pontiacs don't need a high (small) gear and high stall to get into their power band. If they have racing heads on it it may have a wild cam that puts the power high in the rev range


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## leeklm (Mar 11, 2012)

I just went from 3.90 to 3.36 gears, and ahhhh, what a pleasant change! I gained about 10mph at 2500 rpm. You would gain roughly the same going from 3:31 down to 3.08. I thought about 3.08, but thought they would feel a little tall with my 4spd every time I let out the clutch from a stop.


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## Knuckledragger (Nov 25, 2011)

Gran Turismo said:


> Hi.
> Can anybody clarify what the numbers "40 13 GM 965 XO" on the rear diff mean? in relation to the back axle ratio. Maybe just factory part stamps? I cant find the letters on either axle tubes work out the ratio. Thanks.


I'm going to take the time to answer an old question no one else has. On the ring gear, the first numbers stamped are the tooth count on the ring and pinion (in that order). Yours are 40 and 13, which is a 3.08 ratio (40/13 = 3.076). The other numbers are probably pinion bearing distance or some other reference. If you are interested in the gear ratio you have, this is the simplest way of knowing definitely. Pull off the back cover and look at the ring gear. The numbers are there.


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## mrbill (Jan 5, 2013)

30 years ago my first 67 had a 400 TH400 and 3.36. The cam really thumped and didn't come on till about 2500-2700. I lost alot of street races back then because the cam didn't match the gear. I sold the car when I went to college. 
My mid-life crises has me building another one. I loved that cam so everything else is being matched to it. So I'll be running 3.73 with a 200-R4 behind a 428. Man I wish I was further along on this project.... I'm ready! ha ha


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## jtwoods4 (Dec 22, 2011)

I have found that I really like a 3.42 rear with a 2.43 First Gear. I know the 3.42 is a chevy gear but it really works well. I can cruise around 3000 to 3200 rpm at 70. I usually back it down to 2800 just barely below 70. Nice gear, much improved over the 3.73 that was in the car when I got it. The 3.36 Gear mentioned in the original post would be damn near perfect. These engines have so much torque that you dont need any more gear.


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## PontiacJim (Dec 29, 2012)

The Pontiac engine is one of torque and is better suited to ratios in the 3.08 thru 3.55's for cruising. I like to select a cam grind that gives me good low to mid range torque to compliment the engine. Those high revving Chevies might get you off the line, but pulling past them at mid track is fun. Gearing below 3.08 is a bit stiff and not really a performance gear, but will run once you get the car rolling. My brother's 1968 Bonneville had the 2 series gearing and as I read earlier, plant the pedal to the floor at 95 MPH it would down shift to 2nd and pull -it was no slouch once rolling. My '67 GTO convert. had the 3.90's/close ration 4sp. It was fast, shifting was quick, was not practical on the highway, and got 10 MPG. My '70 Judge had 3.55's/4 sp and was great overall -but this was when the speed limit was 55 MPH.

Tire height is very important. You can go with a taller tire and do the same thing as changing your gear ratio. I found this example in an old Pontiac performance book: "When driving your street-strip Pontiac on the highway, bear in mind that the taller the rear tire you have, the fewer RPM you need to cruise at a given speed. In 1964, we ran a GTO with 3.90 gears and 29 1/2 inch tall street tires alongside a buddies '61 Catalina running 3.42 gears and a standard 26" tire. We both cruised along at identical RPM." I run a tall tire myself on my '68 Lemans just to cut down the 3.55's RPM on the highway. You need a good clutch set up if you use a stiff gear with a manual transmission like mine. If you have an original automatic, another trick I have used is to install an "RV towing torque converter" (JC Whitney used to offer these and still may). These converters are tighter and slip less (stall) than the factory (which I believe is about 1800 RPM's). Have an inexpensive valve body shift kit installed, and add a transmission cooler. This will improve your gas mileage and this combo always seemed much more responsive to me.

I have always run the factory 10-bolt rear, but swapping in a Chevy Chevelle 12-bolt was done quite a bit -it just cost more to buy a 12 bolt back then. As I recall, you have to get the correct rear u-joint as the Pontiac uses a larger u-joint cap and Chevy has the smaller -they make a u-joint just for this. I am also certain most any Buick/Olds of the same type body style will fit as well. There are many aftermarket manufactures who make rear ends to fit the GTO/Lemans/Tempest chassis. I opted for a new 9 inch Ford unit for my '68 Lemans that has all the correct brackets to bolt right in. Changing gears is easier as the gears are all part of the removable differential. You can have a couple different sets of gear ratios set up and simply swap them out to suit your needs. Can't do this with the factory 10 bolt or Chevy 12 bolt. Also have the TKO 600 5sp to take advantage of the overdrive. Expensive, requires floor cutting, and fitting modifications. Not for everyone. Installing a later model 4sp auto overdrive trans is an option and was covered in one of the Pontiac magazines years ago. I think it has been made even easier now, can cost initially, but saves in the long run with gas savings and reduced engine wear. I also ran across a website that offered a new Muncie 4 speed which was actually modified as a 3 speed with the 4th gear acting as an overdrive. This would be a bolt in just like factory and appear to look just like a factory Muncie. Changing tire size heights is probably the quickest and easiest, but remember your speedometer will be off, just as it will in changing rear gears, so this has to be corrected with a speedo gear change.


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## anthony moriglioni (Dec 27, 2012)

I have a 69 convertible GTO.. all original numbers.. paint and interior color has changed.. that's it.. 78k original miles. my dad says its got 2.56 rear end.. he stated it wont lay much rubber, but that top end its gonna be up there.. my thing is that if I want to do FAST interstate speeds.. I will take my Ford interceptor up the road.. I am no longer impressed with top end .. after owning a crotch rocket.. what I do enjoy.. getting from zero to 75 as fast as possible, but still go 100 on interstate if need be.. (these cars don't handle well at that speed) Should I just stay with original gears or go with something a little better. .OH.. and its only got the 2 barrel carb. if I go with 4, will that give me the HP addition I want to spin tires when I want, but keep top end without a gear change?


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## Instg8ter (Sep 28, 2010)

i have the 2:56 open rear end with 400 auto 4bb with 2800 stall converter and it will roast the tires. not overly quick light to light but it hums along at 75 at around 2100 RPM and will bury the speedo when i want to. The 4BBl will help yours not be so anemic. With that carrier i think 3:08's the highest gear you can put in it.


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## geeteeohguy (Feb 2, 2008)

anthony, you _could_ go up to a 2.78 gear with your carrier, (if you can find one) but that wouldn't make much difference. I recommend you find a complete 3.23 or 3.36 rear end assembly and bolt it in. Drum to drum. An easy one day project. These were the 'standard' GTO rear ratio in '65, '66, and '67....and area a great all around gear. You'll notice a huge difference around town and out of the hole. Cheap, too.. good .used units can be had for well under $1000.


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## Darth (Apr 30, 2011)

Geeteeohguy, I have a question for you. In your original post you said that your favorite gear was the 3.23. I was wondering what tires you run with that setup. Currently my 65' has American Torque Thrust "D" wheels. I used a calculator for gear ratios and it said that with a 3.23 rear, on 26.30 tires (the silvertowns mounted on Hurst wheels) at 60 MPH I would be turning around 2400-2500 RPM. Is that about what you get? Currently I get about 3200-3500 around 60 MPH. My poor 389 is workin really hard at highway speeds.

I'm gonna restore my 66' 2+2 with a tri-power in a couple of months and put a 200raptor in her I have layin around. Shouldn't have to worry about it with that big ole girl.


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## geeteeohguy (Feb 2, 2008)

Darth, I am running stock diameter tires on the '67 and was running the same on the '65: 26.5". These are/were 225/70/14. I am currently running 15" tires on the back of my 3.36 geared '65 GTO, and these are 27.5" tall, so it effectively reduces my gear ratio to 3.23. I am turning 3000 rpm at about 74-76 mph with that combo. The 3200-3500 rpm you are netting at 60 mph is about right for a 3.55 gear: too high for my preference. You could go to taller tires, and it would help.


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## pcolenutt (Jun 6, 2013)

This is a great thread. I'm running 67 gto 4 speed hurst short shift with 3.73 gears on 225/70R14 cooper cobra radial tyres, yet my wheel diameter is 25" not 26.27 which cooper spec. This means 3000rpm is 58-60mph (hard to tell exactly) and motorway (i live in uk!) driving is hideous, and gas £1.40 per litre, approx $2 litre...... (I think that's $7 gallon on imperial or something similar). That said, it's not my daily driver and I love putting gas in it for the attention the car gets at passers by, so gas mileage isn't top priority, but enjoying driving it is.

I'm looking at going to 3.08 gear which should make 70mph at 2898rpm, and I may increase the wheel diameter to approx 26" which drops it to about 2750. Its a 455ci mild tune so packs a punch, so I'm hoping this ratio will really make driving on uk roads pleasurable yet not impact green light acceleration too much. I therefore want to future proof it, as I may upgrade the engine to a 500hp unit at a later stage so want to be sure the 3.08 is still the right choice.

It's important to measure your actual wheel diameter and plug this into online rpm calculators, don't assume it's spec diameter as this could mean difference of 100rpms as I found. I still don't know why my cooper 225/70R14 are 1.27 inches smaller than what cooper spec!!

Any thoughts on my 3.08 thinking welcome. Any gear manufacturer recommendations also welcome.


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## geeteeohguy (Feb 2, 2008)

3.08 was the 'laziest' ratio offered behind a stick shift Pontiac when these cars were new. It's an excellent all-around gear, great on the open road. With the torque of a 455, an excellent choice. Hard to get in the aftermarket, but shouldn't be a problem sourcing good used parts in this ratio. Be aware that an entire carrier change will be necessary, as a 3.08 ring and pinion won't work with a 3.73 sized carrier. Probably easier and cheaper to simply buy an entire used unit, drum to drum, and bolt it in. That way, you'll have a spare. Shipping to the UK will probably exceed the cost of the rear end, though! Great to hear that a '67 is tearing it up on the other side of the pond!!


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## Darth (Apr 30, 2011)

Yeah cool that a GTO is roaring away in Swinging London.

I see you are from Leeds. Everytime I meet someone from Leeds it makes me think of "The Increasingly Poor Decisions of Todd Margaret."

Also, you guys got the new Alan Partridge movie over there. It isn't released here in the states. Now I have to see if my brother in law can get me a copy somehow.


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## pcolenutt (Jun 6, 2013)

Thatcher was before my time luckily - I'm 35, perhaps the youngest 67 GTO survivor this side of the pond ;-)

Alan Partridge was in my time however and along with Will Ferrell, an all time fav. For those who don't know Alan Partridge, you migh get the movie in the US soon and you might not get the humour, but its kinda like The Office - spoof radio anchor who's politically incorrect in everyday, past it but thinks he's still "it"', drives uncool cars (eg Lexi (singular for Lexus)), and many other relatable attributes to someone cringeworthy you might know.

Anyway we digest... I'll look at options / suppliers for 3.08 with correct carrier. Not sure ill find a full rear end over here but I'll try. I saw a 3.08 for a 10 bolt but was for a 72 onwards TransAm, take it this wont fit?


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## geeteeohguy (Feb 2, 2008)

Nope. You need a carrier for an 8.2" rear, if yours is still stock. The 8.5 units are stronger, though. You could find a good used 3.08 carrier and gears in the US and have it shipped fairly easily, though. I'd recommmend the parts section of the Performance Years forum. Excellent source. Good luck!


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## pcolenutt (Jun 6, 2013)

Many thanks


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## pcolenutt (Jun 6, 2013)

Ok so this thread doesn't let up! I have a 4 speed manual (think Muncie) and so if I go from a 3.73 to 3.08, I'm now informed that the new 1st gear will be longer than setting off in my current 2nd gear, that's assuming I have a 2.2 1st gear ratio in my gearbox and not a wider ratio 2.56. Therefore on a 4spd manual, 1st and reverse will be clutch burners at low seeds in for example traffic, parking etc. and not good at all. Does anyone share this view?

I have in fact got a 65 Chevrolet 10bolt 8.2" rear diff in my 67 GTO so I believe I can only go to a 3.30 gear ratio from 3.73 with this axle. Would you recommend this still ie is the cost worth the gain, or should I bite the bullet and put a 5spd manual in and keep the 3.73 rear gears?

Also, is a mid 70s rear diff with 8.5" gearing bolt on or in fact quite different?

Thanks again!


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## geeteeohguy (Feb 2, 2008)

Why are you assuming that you have a close ratio Muncie box? Close ratio M21 boxes with the 2.20 first gear only came in 3.90-4.33 geared cars. Very uncommon. The vast majority of Muncies are the wide ratio M20, with a 2.56 first gear. 3.08 was a factory option with this set-up, so you will be fine if you do indeed have an M-20 transmission. As I stated, my 'ideal' gear ratio for a 4 speed muncie equipped GTO is about a 3.23. A 3.08 will be superior on the open road and in the top end, though.


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## pcolenutt (Jun 6, 2013)

I was going by what I was informed today in that the close ratio was more popular, which sounds wrong from what you're saying. Thanks for clarifying. I have a 455ci with 8.2" 10 bolt from a 65 Chevelle running 3.73 gears in my 67 GTO. Is it possible someone could have bolted a close ratio M21 to this at all, or is that technically not possible? 

I can (i think) only get to a 3.30 gear with this 8.2" 10 bolt axle. Is that correct? If so, if I want to get to a 3.08, as was mentioned in a previous thread, I'm better getting a full 8.5" 10bolt axle/unit off a donor, do you know which donors bolt right on with minimal rework?

Thanks for the help by the way. I'm new to this so steep learning curve!


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## pcolenutt (Jun 6, 2013)

I missed a question off my post, in that let's say I do have a M21 with 3.73 gears, would the 2.2 ratio in 1st gear be a clutch burner with 3.08 gears? I get the top end cruise speed bit, but I'm trying to confirm if M21 can or cannot work with a 3.08 gear ratios in 1st and reverse ok, or is it too much of a clutch burner and hard to control at traffic lights, parking, slow traffic etc. Thanks


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## geeteeohguy (Feb 2, 2008)

Not an expert on the Chevy 8.2 units. I know that the BOP (Buick, Olds, Pontiac) carriers are such that a 3.36 gear is as tall as you can go if you are running 3.55, 3.90, or 4.33 gears. For 3.08, you would need a different carrier assembly, the on that works for 2.93, 3.08, and 3.23. I do know that the 8.5 unit is much stronger than the 8.2, and also more plentiful. I do not know which one would be best for your application. You could try the Performance Years forum and probably come up with the right answer, though! As a side note, the person who informed you that the close ratio was the most popular is mis-informed. It was popular with racers, but only a small percentage of GTO's got them. Very few real 3.90-4.33 GTO's out there. They were _vastly_ outnumbered by the very popular wide ratio M-20 cars. If you've ever driven a 3.90-4.33 car on the street, you'll know why they were unpopular, too.


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## rickm (Feb 8, 2012)

the 3:23 was a common ratio in early gto's that rolled off the assembly line with the 3-speed manual trans. my '65 coupe came that way, but I changed to a m-20 with 3:55 s. im happy with it for the driving that I do with the car.


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## BearGFR (Aug 25, 2008)

rickm said:


> the 3:23 was a common ratio in early gto's that rolled off the assembly line with the 3-speed manual trans. my '65 coupe came that way, but I changed to a m-20 with 3:55 s. im happy with it for the driving that I do with the car.


3.23 is what the Beast had originally and that ratio was a good compromise for both "freeway" and "frolic" 

The 3.50's it has now are a little more on the "frolic" side, but for the majority of the driving I ask it to do now they're purt near perfect. Matching the ratio to intended use is definitely the way to do it, just as Pontiac knew back in the day. There's a reason that the base ratio for Ram Air IV cars was 3.90 (with 4.33 being optional) and neither one was available with A/C. 

Bear


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## rexs73gto (Nov 25, 2012)

I as my name says have a 73 GTO & I run 3:73's in the rear end. I've had them in there for about 20+ years now. I bought my car new with 3:08's . Out on the road the 3:08's were great, you could get out & go & my top end was some where around 140-150. I don't really know as I've only went as fast as I could once with it & it got me a ticket in 1975 going back to my ship when I was late getting back. The cop was really great & we had a long talk & he & the other cop had a good laugh about it. I ended up getting a warning ticket out of it. A few years later I switched to a 4 speed & hated the 3:08's in it then. I installed the 3:73's in it a years later & I love those gears. I get around 16 MPG running about 60 MPH. If I step it up from there the mileage goes down but not enough to want to go o a lower gear set. With the 3:73's & the 4 speed I run , it's an M-22. It comes out of the hole great & I run mid 11's in the 1/4 so I will keep them. Those gears are the best thing I have ever done for the car. I am running a 462 with Eldo. alum. heads & a RA IV cam 1:65 rockers, performer RPM intake & a Q-jet. The pistons are SRP forged with Eagle H-beam rods. I have RA IV exhaust manifolds to. I've had several different combos of engines in my 73 over the years but so far this set up works the best for me.


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## germangoatowner (Apr 29, 2014)

I have a 69 goat with a 455. i have changed the ratio to 3.0. since I did this the car runs much smoother. And do not worry about the performance. Still enough power to smoke some big cars. 


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## RunninLeMans (Apr 3, 2014)

Wow, great thread. I just read the whole thing looking for the answer to this question - will a 8.2 BOP rear end from a 1967-1972 A-body bolt right up in my '64 A-body? I understand it's an inch wider, I was more concerned with the spring pads, control arm and shock mounts, etc. Thanks...


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## geeteeohguy (Feb 2, 2008)

Yep. Straight bolt in. The later rears sometimes have bolt-on lower retainer plates for the bottom coil on the springs. These are not really important..


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## RunninLeMans (Apr 3, 2014)

Thanks, Jeff, opens up the options...


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## RunninLeMans (Apr 3, 2014)

Ended up with a '68 GM 8.2 with an Eaton 3.08 posi from JD Race and Restoration. Got a good deal and he did a great job with the pallet and wrapping. I was leaning toward the 3.23, but I have to say I love this 3.08 with the M20 now that I've put a few miles on it. I also got the sway bar and boxed control arm kit from Ames, Gas-adjust shocks and did the rest of the bushings while I had it apart, handles great now. Road trip tomorrow to stretch it out a little. I set aside the BOP 2.56 one-legger for future, uh, whatever. 

Great thread, it was good to read everyone's stories before pulling the trigger.


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## geeteeohguy (Feb 2, 2008)

3.08 was the tallest gear Pontiac put behind a 4 speed. It will be decent off the line, and excellent at cruise, mid-range, and top end. For a car that's driven on today's $4 gas, you'll never regret it. Slightly less oomph than the 3.23 from a dead stop, but far superior at highway speeds, and better overall mpg. Your engine will use less gas, run cooler, and run longer. Great choice, IMO.


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## GTO70455 (Feb 10, 2009)

I have run 3:55's in a 70 GTO and find it the best of both worlds. Its behind a stroked 474 CID motor. Behind the motor is a new autogear M-22. The car has been to North Carolina, and up to to Maine. Does about 3000rpm at 70mph. I was running a 750 Holly 4150, but found out replacing the carb with a AED 850HO carb the car breaths a lot easily and less restrictive that was noticeable. The gas mileage on the highway actually got better by a few points.


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## RunninLeMans (Apr 3, 2014)

Yea, from a dead stop it needs a little feathering, but not bad. I put 240 miles on it Saturday, runs about 2850 rpm at 70 mph with 25.5" diameter tires. Even with some 'spirited' driving it got almost 20 miles to the gallon!


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## 1965goat (Sep 8, 2014)

I have a 65 and I have a 12 bolt but I'm not sure the gears. Just wondering what a good gear ratio for a 12 bolt would be because I wanna change out the differential for a new one.


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## 1965goat (Sep 8, 2014)

*gears for my goat*

would a 3.23 auburn 10 bolt be a good differential for my 65? im talkin the high performance series 10 bolt. i have a 12 bolt now but i wanna swap out. just wondering if this is a good buy for street/strip riding


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## Too Many Projects (Nov 15, 2008)

1965goat said:


> would a 3.23 auburn 10 bolt be a good differential for my 65? im talkin the high performance series 10 bolt. i have a 12 bolt now but i wanna swap out. just wondering if this is a good buy for street/strip riding


It all depends on the hp level and transmission you have. 3.23 with an automatic and a stall converter can be a good street combo but not great for drag racing. What do you intend to use the car for ?


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## Darth (Apr 30, 2011)

Question. I have a 65' GTO, fully restored. It has the 389 with the factory 4 barrel and a 4 speed transmission. My problem is with the gearing. I don't know if it can be fixed in the tranny or the rear end. First gear is just WWWAAAAAAYYY to high. My 69 Camaro and 2013 Challenger will take off at idle when I ease out on the clutch. The goat will die if I don't give it the beans with the gas pedal. 2nd and 3rd are okay, and 4th is WWWAAAAAAAYYY to low. Like, no discernible difference between 3 and 4 gear. For example, if I am cruising down the highway at 55 MPH doing around 3000 RPM, and I shift into 4, it drops to about 2950 RPM. D I need to see about regearing the rear end or is this something that can be fixed with the transmission? Thanks.


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## Too Many Projects (Nov 15, 2008)

It sounds like the transmission is not an original. The rpm drop between gears on a Muncie is generally 500 rpm, with the exception of an M20 between 1st and 2nd is about 750 rpm.

If the rear gear ratio is 2.73-3.08 an M21 will give you a high ratio requiring slipping the clutch to get moving. The M20 was the standard trans from the factory with a 2.52 first gear ratio rather than the 2.20 of the M21.


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## Darth (Apr 30, 2011)

It's got an M-22 Rockcrusher in it.


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## Too Many Projects (Nov 15, 2008)

M22 is the same gear ratios as an M21 with the 2.20 1st gear. If your tach only drops 100-150 rpm with the 3-4 shift, your tach isn't accurate.

The M21/22 with highway gears in the rear will create the need to slip the clutch to get going. They were originally installed with axle ratios of 3.73 or deeper.


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## 60sMotorhead (Nov 19, 2014)

Stuck a $50 (in 1985) wrecking yard 2.56 (open) rear axle in my 69 428/62 heads TH400 GTO convertible adding 235-75-15 tires (~28.5") before going on a road trip back then. Got about 17 mpg at 70-80 mph at 2200-2600 rpm. Never ran any quarters, but with the torque, it was good enough for me... would break tire loose from 35 mph punch, shift out of 1st around 60 and 2nd just over 90 (got speedo calibrated but never regeared). Took it up to 4000 rpm once, was going just over 125 mph and still accelerating at a decent rate - I was older then (than when racing the 70 455 down by the river in the 70s) and realized if the car flipped I'd be dead so backed off - it was a bit scary because with stock suspension the car didn't handle so good. Car ran very smooth. That engine blew (dropped valve) so will be building a stroker now - sure appreciate this site for all the knowledge here. I could never get traction but would be nice to try with the long legs - though seems something would give (rear axle, u-joints, ???). That car is 3553 lbs according to oldride.com (about 500 heavier than a coupe).

I still have the old rear axle (WH is 3.55 open?). When I got the car (for $1800 in '84) it was primer gray with a knocking rod and fairly loud exhaust - roommate dubbed it the Road Warrior. Drove a bit before teardown and while coming down a hill in Sunnyvale CA, in right lane of 3-lane road toward a red light, there was a 260Z and ~70 Camaro sitting in the two left lanes at a stoplight... I was a couple car lengths back when the light changed and it was obvious they were going to run each other... and not paying attention to me coming up from behind. I mashed the pedal at about 20 mph, took off like a blaring rocket, and blew past both - as I passed I looked over to see the Z guy's wide eyes and dropped jaw, and left both far behind... introduced them to Pontiac and I got hooked on acceleration. The 69 was much faster than the stock 70 (though I think the 70 GTO is one of the classiest looking cars of all time).


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## geeteeohguy (Feb 2, 2008)

This is probably buried somewhere in this thread, but I have had a 2.56 Safe-T-Track in my otherwise stock '67 GTO convertible with a TH400 for about the past 5-6 years. I removed and mothballed the oem 3.36 open diff. I also re-geared the speedo and calibrated it. I_ love_ it for the type of driving I do with the car, which is long road trips. 20-21 mpg at 75-80 mph, and shifts into 3rd gear at about 105-107 at WOT. If you are going 85-90, and floor it, it kicks down into passing gear and gets with the program. VERY long legs. That said, these cars kind of hit a wall at 130-135 MPH....the front end starts to lift, the steering gets very, very light, and it gets.....interesting. I've seen old non-aero drag cars flip at speed (thus spoilers and dams later on) and I have been to that 'edge'. Funny how well air dams and spoilers work, as well as aerodynamics.....went 145 MPH in a friend's '74 Firebird, and it was planted and solid at that speed....totally unlike my older GTO's.


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## AZgoatguy (Oct 13, 2011)

I too am running a 2.56 Safe-T-Track and enjoy it for the driving I do these days. I installed it in my '66 Goat-a-mino about three years ago to see what the driving/performance differences would be over the 3.23 Safe-T-Track. This car is my daily around town and to Home Depot hauler; see my forum home page for an album about it. The engine is a '66 Goat 389 with Tri-Power and trans is a TH-400 with an RV kit in it. The engine has plenty of torque to make this ratio work well in city driving and when cruising the highways/Interstates it has the grunt to pass easily. Gas mileage is somewhat improved over the 3.23. Performance wise you still feel good acceleration but it's not brutal or pushing you hard back into the seat, though still great for rocketing up the Interstate on-ramp. The one thing I will be changing, and am in the process of doing it now, is to put in a higher stall torque converter. With this engine and the stock TH-400 converter I'm not able to power-brake without stalling the engine, just cannot get into the bottom of the horsepower band. So for a little more grunt off the line, even if I still can't power-brake, I'm putting in a stock TH-350 converter which has a bit higher stall than the TH-400 and it has the same durability. My transmission guy said to do this and save $$ over an aftermarket converter, unless you want to go nuts on stall speed. I hope he's right, we'll see.
And 60sMotorhead... I liked your reminiscing on the 260Z and 70 Camaro, fun stuff! We all have stories of our Goats and yesterdays races, and my stories start in Dec of 1968 when I bought my first one - '64 Tri-Power, 4-spd, 3.23, Sunfire Red convertible. Gas-Tires-Oil cruising Speedway Blvd in Tucson on many an evening, won some and lost some... and it was fun, fun, fun! For several years I thought my car was fast (I had added a cam, headers, etc) but then a buddy of mine bought a very nice used '67 Goat off a corner car lot... it was an HO, 4-spd, 4.33 Safe-T-Track... he ate me alive, now I knew was fast was! His car became well known on Speedway and always won its races - a 426 Hemi Roadrunner managed a tie with him, short a fender length. Style wise I like the '67 best, love the grill with stacked headlights.
Cheers. Gary, in Tucson.


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## Goat Roper (Oct 28, 2014)

My car has a 2.93 pegleg rear end and it came with 225/70 Relines.
It would break the tire loose and chirp going into second but they were too tall and were rubbing on the fenders.
I just put a set of 225/60-15 T/As on it and now it will light the tire and lay a decent strip going into second.
It also stops a lot better so tire diameter makes a huge difference.
I don't hot rod the car so this ratio is fine and I don't think it is worth the bucks for a posi.

Since I just bought the car I figured I should service the tranny and bought a filter from the local parts guy according to application 67 w/ TH-400.
When I pulled the pan the filter was wrong it had a long rectangular filter on the driver's side.
I was told this was the original tranny but the filter according to application is a 400 out of a Caddy.
Did they use Caddy trannys in '67 or has this one been replaced?
Fluid was very clean and bright red and nothing to speak of in the bottom of the pan.


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## 60sMotorhead (Nov 19, 2014)

AZgoatguy: Cool Goat-a-mino - didn't know Canadian cars have different grilles etc. About the 67 Goats (I like them too - the stacked headlights with the diamond pattern wire grille is classy)... We used to run between the rivers (St. Louis into Alton) around 1975. A big guy had a BEAUTIFUL red 67 with a black vinyl top (you could see that vinyl pattern when the light hit it from behind), except the front clip was primered. I asked if he bought it like that and he said no - it was perfect when he bought it from some old lady until he hit a telephone pole with it.... ouch - the older cars were fast but they didn't handle or stop too good. I was driving a 70 455 GTO TH400 then (tan metallic with tan vinyl top) - I usually won until some 340 Duster beat me - and later got beat by Frank Marzuco with his 69 SS 396 Chevelle (he said about my GTO, "I thought that thing was fast") - both those cars had 4-speeds. I was humbled... Not sure what the deal was - had GTO up to 132mph once, but it really wasn't that fast off the line. I didn't know much about tuning then, but seemed it just didn't have the punch of the 69 428... I think it was heavier and the engine had lower compression (just looked up - hardtop was 600 lbs heavier than a 69, but only about 100 heavier than my 69 convertible). Never remember it pinging, so maybe could have advanced timing more and run it with Sunoco 101 (and look what I just found... brings back memories - inet is cool)
Tom McMahon: Sunoco Blend-O-Matic Gas Pump


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## 60sMotorhead (Nov 19, 2014)

to Geeteeohguy: yeah that is a weird feeling when it kicks down from a 90 punch - the car never seemed to stop accelerating... not super fast, but constant. I also felt the 69 lightening up around 120 - I was getting a weird feeling in my stomach (and brain) that "to keep doing is not a good idea..."never driven something with air dams, but they also made made improvements in handling between 70 and 74. Almost forgot - l must have had the top down when going that fast in the GTO... I still have my college car, a 68 Impala convertible (rustbucket that I paid $300 for in Kansas City in 1980 - 350K miles on it now, though it's parked in backyard - replaced all bolt on panels with those from a clean CA car that I paid $75 for around '85 [now thinking was a shame to tear that car apart]). Anyway, the top was pretty worn out in '85, but still kept rain out - when I hit about 90 on the highway with top up, I started hearing this sound (for some reason I thought of a lot of bats flapping their wings) and about 5 seconds later the top ripped off completely... I replaced it (myself) with a lifetime guarantee top from JC Whitney - it's getting old again, and I called them about 5 years ago and asked if they'd honor the guarantee. They said yes if I had the receipt, which I still do (they printed them in ink back then, not the disappearing thermal stuff so many use now). They don't sell lifetime tops anymore - are 5-year


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## RunninLeMans (Apr 3, 2014)

Darth - a little late with this reply, but my M20 is 2.54 1st, then 1.88 and 1.42 2nd and 3rd. I checked 'em with a dial indicator on the rear brake hub, just to see if the method worked. If I shift at 3,000 rpm it drops about 650 rpm from 1st to second, 550 rpm from 2nd to third and 900 rpm from 3rd to 4th.


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## hotcharity95 (Jan 4, 2015)

*lemans 2 speed*

hi y'all, I have read a ton on this site and it is beyond sweet. can I put 3.90 posi (that I have) in my super turbine 300 68 lemans? how uncomfortable will this be on the highway? what are the tallest gears I can use with a 2 speed?

Would I be better off putting in a th350 first to see what performance gains there are, if any? It's a dog off the line but really has great highway gear (2.78 probably - wasn't this standard for lemans?) or wait until after rear end is done to see if I need to swap the tranny?

Thanks, CJ


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## geeteeohguy (Feb 2, 2008)

A 3.90 rear gear will be terrible on the highway behind any transmission without an overdrive. You would be MUCH better off keeping your 2.78 gear and bolting in a TH350. Cheaper, and way better to drive. Your car will feel like you added 100 horsepower, literall. The ST300 has a 1.76 first gear, wheras the TH350 has something like a 2.75 first gear. HUGE difference in off the line punch. Both transmissions have a 1:1 final drive, so those 3.90's would have you cruising at 50-55mph at 3000 rpm. If you want a little more low end grunt after installing the TH350, you could install a rear end with 2.93-3.08-3.23 gears. You would lose speed on the top end, though. Also, in this day of expensive gas, the TH350 is a win-win with your current 2.78's: you'll get better gas mileage around town and great gas mileage on the open road. I installed 2.56 gears in the back of my '67 GTO convertible with a TH400 trans and stock engine, and it gets over 20mph at 75-80 mph. I drive the wheels off of it.


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## Longs (Jul 21, 2013)

I have a 67 GTO, 335 HP 400 with Turbo 400 dual-gate, bought it in my youth in 1981. The car has factory A/C and came with a 2.93 posi. A couple of years into owning it, I had a bad axle bearing and, wanting to make the car a little faster, a buddy and I replaced the 2.93 with a 3.36 posi from another '67 GTO. I am also running larger tires than stock (225-70-15). I still have the 2.93 gears and posi that came out of the car 30 years ago.

Since I don't race the car at this point, either on the street or the track, I was thinking about going back to the 2.93 posi. Would it really be worth it, or am I not going to notice that much difference in highway RPMs? 

I ran across a calculator that considers the gears and the tires, and together estimates that I'm probably running a hair over 56 mph when the speedometer shows 60, so I am putting a few extra miles on the odometer running this way - and I've probably put 25K on the car since the swap. This is the calculator:

http://www.roversd1.nl/sd1web/wheelcalc.html

I don't have access to a shop, I have a garage and a decent array of tools, no helper, so I'm not sure that I'd try to do it myself, it's been a long time since I did the job! What would you do?

This calculator estimates that if I changed from the 3.36 to the 2.93 with the 225-70-15 tires, my RPMs at 70 mph would go from 2,884 to 2,515. Worth it?

http://www.wallaceracing.com/calc-gear-tire-rpm-mph.php


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## Pinion head (Jan 3, 2015)

Longs, Welcome! Would suggest swapping from the 3.36 to the 2.93, ESP if the 2.93 safe-t-track was in good shape when you previously pulled it out. 

What follows can be done in under 2 1/2 hours on a flat driveway without airtools. Have done it many times. What matters is the brakes on the current 3.36 rear are in good shape. 

Ready to go? Loosen the lugnuts slightly on the rear wheels, jack the rearend of the car up under the center of the r/e hsg and put good sized jack stands under the cars side framerails in front of the rear. Next, pull the lugnuts, and tires and wheels off. Next remove the drums off the currently installed rear (the 3.36 Pontiac 8.2). 

Next, unbolt the axles, takes a 9/16" socket and go through the access hole in the axle flange. Remove all 4 nuts and slide the axles out. They should pop right out, you can bump the inside of the axle flange with a large pickle fork off the top of the brake shoes if thy are a little tight. Next, unbolt the lower shock mount from the housing with an 11/16" socket. Next, slide the backing plates out slightly off the t-bolts of the 3.36 rear. With a piece of coat hanger or string, hang the backing plates up so they don't drop too much. By going this route, you are keeping the rear brake lines intact, from backing plate to backing plate, and there will be no need to have to bleed the brakes. 

Next, remove the small bolt that holds the brass junction block of the rear brake hose. Pry the small tabs up and let the steel brake lines loose. Both lines and backing plate should now be unattached from the 3.36 rear. Next, remove the nuts and lock washers from the ubolts holding the driveshaft to the pinion flange. Bump the ubolts out and pry the driveshaft forward. Carefully drop the rear of the driveshaft, keep the yoke forward, in the transmission, or you will have a mess.

Last, going to remove the four 3/4" headed long bolts and nuts that hold the rearend housing to the upper and lower control arms. I usually remove the bolts out of the back of the lower arms first, then unbolt and remove the upper bolts. Once you get this far, you can slowly let the assembled rearend housing down on the floorjack and pull the now loose rearend hsg at an angle toward the side of car. that way, you can hop the shocks out of the way.

On the 2.93 rear, remove the old drums (if so equipped), axles, and backing plates, pull the rear cover, and carefully inspect the teeth on the the ring and pinion. As long as the 2.93 rear hasn't been setting outside on the ground, it probably won't have drawn up moisture from the ground and created rust at one point on the ring and pinion. If no rust, you should be fine. With 1 3/4 qts of new 80-90 rearend grease and a small bottle of GM posi additive installed, you can reinstall the cover with a gasket, and button it up. With the old backing plate and old lines removed, the 2.93 rear can now carefully go onto the cup of the big floor jack. Going back in , your only obstacle is the shocks hanging down slightly. There is usually enough play in the upper shock rubber mounts that you can manipulate the shocks if they are in the way. Once you get the 2.93 rear up and bolted in, look at the axles from both rears, most likely each has the sealed axle bearings (no external seals). If the axles out of the 3.36 rear are same length as the ones out of the 2.93, and the sealed axle bearings were replaced on the 3.36 rears axles, previously, and they don't now have 50k miles on the replacement bearings, you can substitute the axles out of the 3.36 into the 2.93 rear.

Replace the steel lines under the tabs, then button everything up. Helps to have a buddy, or a son to hand tools, and help roll the rearend into place. Do this several times, and you can actually do it proficiently in under two hours.


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## Longs (Jul 21, 2013)

Pinion Head, Thanks for that detailed explanation. You must have misunderstood my question, though, as it sound like your instructions were for changing the entire rear, not just the ring/pinion/carrier, etc. When I changed these years ago, that's all I changed. The housing and the rest of the rear is still the original. I just swapped the innards within the pumpkin, so to speak.


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## Pinion head (Jan 3, 2015)

Longs, yes, missed that the original ring and pinion had been removed and rear was then set up with a set of GM 3.36's. quickly reading you post, read it like you had the 2.93 rear loose, but it had a bad axle bearing. How's that for reading comprehension 

Still see the swap back to the original 2.93's as the best solution.
If the original 2.93 pinion still has the original piñon shim under the large pinion bearing, the whole process is going to be sped up. The original pinion is going to be replaced into the original hsg, and with a minimum of a new crush sleeve, new 1 1/8" pinion nut and new pinion seal, * with the right tools and a lot of care*, the pinion can be replaced and pinion depth and pinion drag can be reestablished. of course, pinion bearings and races may need to be replaced, as well.

Once pinion depth and drag are correct, can move to setting backlash. A longtime GM differential builder should have a large selection of cast side shims and thin side shims. All of my cast side spares are organized by style, to .0005 in thickness, in freezer bags. This speeds up looking for the correct thickness cast side spacer, so, can get onto installing a GM service spacer and thin side shim on the other side. If you did save the two original cast side spacers, when he 2.93 gear and carrier was removed, that is going to help speed things up as well. 

Good luck on this, I can go into more detail if needed. HD 8.5's & strengthened 12 bolts are what I mainly build today, but have gone through many Pontiac 8.2's along with all of oddball 10 bolt GM rears of the late '60's.


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## geeteeohguy (Feb 2, 2008)

A 2.93 rear ratio for a '67 GTO with TH400 is in my opinion the perfect ratio. A MUCH better street gear than a 3.36....excellent power mid range, and great top end and fuel mileage. You'll find that you drive the car a lot more, as it will use much less fuel, too. Go for it!


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## dd68gto (Nov 14, 2012)

geeteeohguy said:


> A 2.93 rear ratio for a '67 GTO with TH400 is in my opinion the perfect ratio. A MUCH better street gear than a 3.36....excellent power mid range, and great top end and fuel mileage. You'll find that you drive the car a lot more, as it will use much less fuel, too. Go for it!


Run that in my 68 and love it . I could not agree more and still a blast to drive. Doug


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## gfdcar1 (Feb 26, 2020)

dd68gto said:


> Run that in my 68 and love it . I could not agree more and still a blast to drive. Doug


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## gfdcar1 (Feb 26, 2020)

dd68gto said:


> Run that in my 68 and love it . I could not agree more and still a blast to drive. Doug


I have a 68 GTO with a 3.36 Posi in it if I put the 2.93 will I have to change the carrier also?


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## HiVolts (Jan 27, 2020)

3.50, Moser 9 inch in mine with 4L80E. Butler built 461. Perfect gear. Spins 1900 at around 60 mph.


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## BearGFR (Aug 25, 2008)

HiVolts said:


> 3.50, Moser 9 inch in mine with 4L80E. Butler built 461. Perfect gear. Spins 1900 at around 60 mph.


That's what I'm wishing was in mine. I already have the Moser 9" and 3.50's I'd love to hear details of your 4L80E conversion, how it's built, did you modify the shifter, trans tunnel mods, etc.

Bear


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## HiVolts (Jan 27, 2020)

BearGFR said:


> That's what I'm wishing was in mine. I already have the Moser 9" and 3.50's I'd love to hear details of your 4L80E conversion, how it's built, did you modify the shifter, trans tunnel mods, etc.
> 
> Bear



Baer,
I’d love to tell you more but I bought it that way. Where you located? Come on over and check it out. I do know it’s a TCI street fighter with a Saturday night special stall. Mark Williams driveshaft going to a Daytona Pinion with Detroit Locker 31 spline. Butler built 461, 550hp, 580 torque.


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## Destroy (Mar 21, 2020)

VettenGoat said:


> Thanks guys, I've been having the same inner dilemma. The 65 originally had 3:90s like Rukees, but they are long gone several owners ago and now it has a wrong 1971 rear in it with 3:23s. So I am still looking for a 65 rear and thinking about what ratio to use with the 421. Geetoguy is right, we're not kids anymore and gas isn't .35 a gallon so 3:90s are out. I'm tossing up whether to go 3:55s or 3;73s. Anyone running 3:73s? Thoughts?
> Mike


Mike....I’m running 3:31’s in my rear behind a Muncie RockCrusher 4 speed powered by a 65 421 police interceptor....I wouldn’t want it any other way !!!....I can get rubber in all 4 gears...125 in a quarter mile and that’s what she tops out at..in first and 2nd I can pull the front end off the ground 3 feet....wicked quick and love it! 
Troy


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## Tranman69 (Apr 1, 2020)

geeteeohguy said:


> Hi. I'm posting a new thread because I didn't want to hijack another thread that this subject came up on: Gear ratios. I was bragging about my "racing" days, and gear ratios were mentioned. The following is some information that I have learned over the years, and the following opinions on gear choice are my opinions and nothing else. I am no engineer. I've run GTO's over the years with ratio's from 2.56:1 to 4.56:1. Stock early GTO's with stickshift usually came through with 3.55 gears, and aut0 cars had 3.36 gears standard. The 3.55 (4-Series) carrier could accomodate gears from 4.88 or so down to 3.36. The 3 series carriers could accomodate gears from 3.23 down to 2.51. I found that "back in the day", with cheap gas and road noise a fact of life, the 3.55 gears were okay.....the '66 tended to be running about 3200 rpm at 70mph....right in the power band. The speed limit was 55 at the time.Top end was ok. Low end was great. Good "all around" gear, back then. Now, 3200 rpm at 70 is too darn high. Too much noise, too much fuel, and with a big block Pontiac, uneeded. I ran a 3.90 gear in a '65 for a while. That car HATED the hiway. Top end was 107 mph, at redline. It would get there really quick, though. I changed out those 3.90's with a 3.36 gearset (the tallest gearset I could run in my 4 series carrier) back in 1990. Changed the car. Now, it loves 70 mph. It feels just about as strong out of the hole (Still can't hook up....tire smoke central), my fuel economy went way up, and my road noise went way down. I had another '65 with a 3.23 gear and a 4-speed, and the 3.23 is my FAVORITE gear ratio for these cars. It does everything well: accellerate, cruise, and top end. I drove a '65 with a 2.56 gear. GREAT top end, doggy as hell off the line. Too extreme. A friend had a 2.93 gear in his '67. The car would kick down into 2nd gear (turbo 400) at 85-90 mph. We smoked a 427 '65 Corvette on the hiway one day....he was running 4.11's and was done at around 105mph. The '67 would top 140 mph, I'm sure. Another friend had a 4.88 geared, dual quad 455 '66. We broke the wheel studs on the rear wheels getting on the freeway one day. He jumped on it, and there we were. The car would lay rubber when you got on it at 65mph., in 4th gear. Scary. cruising speed was 55 mph. Got about 8mpg at 55! My convertible '67 has the stock, 3.36 gearset. I wish it had a 3.23. It is a little busier at speed than I wish it was. I guess I'm getting old...I like running at 75 mph with minimum road noise and fuel consumption. Today, there's a lot of options with overdrives, lock-up converters, etc. If you want to modify your GTO and add a 700R4 trans, or add a 5 or 6 speed stick, you can run a 3.55 or 4.11 gear and STILL cruise at high speeds. If you're like me, and don't want to cut up your original old Goat, you have to choose what gear ratio best suits YOUR needs. For this guy, it's 3.23's.
> Jeff


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## Tranman69 (Apr 1, 2020)

Jeff,

Great breakdown of gears and success with each. I just bought a 65 and it's got 3:90 gears in it...do you have any recommended resources for finding a 3:23 set?

Matt


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## Bub (Oct 11, 2020)

I am about to put a posi 3:42 in my 64 lemans. Im running afour speed muncie and a bored out 327 double hump high compression heads that somebody cammed. Ill let you guys know if it ends up a dream or a nightmare. My carrier is made for c clip axles and i believe i have flanged axles in my car. Does anybody know if this will work or do i need to buy new c clip axles for the differential swap?


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## BearGFR (Aug 25, 2008)

That little 327 is probably going to need a lot of gear, especially if it's been 'cammed'. You're also going to need some way to retain the axles in the housing - grooves on the ends for the clips, c-clip eliminators, or provisions for the backing plate/bearing retainers on the outboard ends of the housing. 

Bear


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## Bub (Oct 11, 2020)

Sooooo.........what do you mean by "a lot of gear". Do you think 3:42 is too much power, not enough speed at the end or too much top end and not enough take off. And i kinda figured i was going to have to buy new c clip axles. Was hoping there was a way around it but if i have to, i will


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## PontiacJim (Dec 29, 2012)

Bub said:


> Sooooo.........what do you mean by "a lot of gear". Do you think 3:42 is too much power, not enough speed at the end or too much top end and not enough take off. And i kinda figured i was going to have to buy new c clip axles. Was hoping there was a way around it but if i have to, i will


Know what is in the engine and what the cam power range is is what can be used to determine your rear gears.

Small blocks can easily be built to push 7,200 - 7,500 RPM's all day long with forged parts, the good heads, and a cam that will begin pulling in the 3,500 RPM range. This would also require high compression and race gas - don't look to this engine for gas mileage.

So, 3.42 could be too low with a hot small block where it needs no less than a 3.73's and may do better with 4.11, 4.56 gearing to keep it happy. 3.42's could bog the engine if it has the higher RPM capabilities tied in with the cam.


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## BearGFR (Aug 25, 2008)

Bub said:


> Sooooo.........what do you mean by "a lot of gear". Do you think 3:42 is too much power, not enough speed at the end or too much top end and not enough take off. And i kinda figured i was going to have to buy new c clip axles. Was hoping there was a way around it but if i have to, i will


No one can get specific without knowing a ton of detail about how your car is set up, but in general, little chevys don't make much low rpm torque to start with and 'big' cams only make that worse. 

Like PJ said, I'd it's "built right" it can be pretty comfortable running high rpm, and 'shorter' gears help with that. 

Bear


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## Bub (Oct 11, 2020)

Gotcha!!!! Well.......at this point, there is no turning back. I stumbled blindly into the carrier, ring and pinion and all bearings and seals for $150. Whats back there now is like a 2:76 which is ungodly fast once you get past the 0-60 time of approximately 10 days. So ill get it all hooked up with the v-gate ramrod shifter i ordered today and if it doesnt work out i may be able to put 3:73s right in that same carrier. Ill be sure to let you guys know how it works and i really appreciate the opinions, im new at this stuff!!!!!!


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## Boomstick (Sep 13, 2021)

My 69, 3:23, th400, 275/35/18's


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## James123 (8 mo ago)

geeteeohguy said:


> Hi. I'm posting a new thread because I didn't want to hijack another thread that this subject came up on: Gear ratios. I was bragging about my "racing" days, and gear ratios were mentioned. The following is some information that I have learned over the years, and the following opinions on gear choice are my opinions and nothing else. I am no engineer. I've run GTO's over the years with ratio's from 2.56:1 to 4.56:1. Stock early GTO's with stickshift usually came through with 3.55 gears, and aut0 cars had 3.36 gears standard. The 3.55 (4-Series) carrier could accomodate gears from 4.88 or so down to 3.36. The 3 series carriers could accomodate gears from 3.23 down to 2.51. I found that "back in the day", with cheap gas and road noise a fact of life, the 3.55 gears were okay.....the '66 tended to be running about 3200 rpm at 70mph....right in the power band. The speed limit was 55 at the time.Top end was ok. Low end was great. Good "all around" gear, back then. Now, 3200 rpm at 70 is too darn high. Too much noise, too much fuel, and with a big block Pontiac, uneeded. I ran a 3.90 gear in a '65 for a while. That car HATED the hiway. Top end was 107 mph, at redline. It would get there really quick, though. I changed out those 3.90's with a 3.36 gearset (the tallest gearset I could run in my 4 series carrier) back in 1990. Changed the car. Now, it loves 70 mph. It feels just about as strong out of the hole (Still can't hook up....tire smoke central), my fuel economy went way up, and my road noise went way down. I had another '65 with a 3.23 gear and a 4-speed, and the 3.23 is my FAVORITE gear ratio for these cars. It does everything well: accellerate, cruise, and top end. I drove a '65 with a 2.56 gear. GREAT top end, doggy as hell off the line. Too extreme. A friend had a 2.93 gear in his '67. The car would kick down into 2nd gear (turbo 400) at 85-90 mph. We smoked a 427 '65 Corvette on the hiway one day....he was running 4.11's and was done at around 105mph. The '67 would top 140 mph, I'm sure. Another friend had a 4.88 geared, dual quad 455 '66. We broke the wheel studs on the rear wheels getting on the freeway one day. He jumped on it, and there we were. The car would lay rubber when you got on it at 65mph., in 4th gear. Scary. cruising speed was 55 mph. Got about 8mpg at 55! My convertible '67 has the stock, 3.36 gearset. I wish it had a 3.23. It is a little busier at speed than I wish it was. I guess I'm getting old...I like running at 75 mph with minimum road noise and fuel consumption. Today, there's a lot of options with overdrives, lock-up converters, etc. If you want to modify your GTO and add a 700R4 trans, or add a 5 or 6 speed stick, you can run a 3.55 or 4.11 gear and STILL cruise at high speeds. If you're like me, and don't want to cut up your original old Goat, you have to choose what gear ratio best suits YOUR needs. For this guy, it's 3.23's.
> Jeff


Still a great post after all these years. But.... You kind of cast doubt with your statement about "big block Pontiac". LoL


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## PontiacJim (Dec 29, 2012)

James123 said:


> Still a great post after all these years. But.... You kind of cast doubt with your statement about "big block Pontiac". LoL



Holy chit Batman! *geeteeohguy* must have been smoking those left handed California cigarettes that day because he certainly knows better. Can't believe we missed that one. Someone wash that man's mouth out with some Chevy big block wheel bearing grease and whack his pee-pee. 

"Too much noise, too much fuel, and with a *big block* Pontiac, uneeded. I ran a 3.90 gear in a '65 for a while."


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## HaroldBlakney (6 mo ago)

Interesting thread and thank you. Brings back fun memories. I owned a 66 GTO convertible that I put together back in ‘78-81. The shell was from someone the raced it on an oval. I put in a 389 and a turbo 400 in it both of which I rebuilt from the block and xmission case. It came with a 2.56 rear. The frame I think was twisted as it needed spacers on one rear wheel. Got a lot of tickets. Off the line it couldn’t get out of its own way. But given 5 miles I could pass anyone at very scary speeds. Speedometer was never right but that was not a good defense in court against the speeding tickets. The memorable moment was when another GTO passed me on the highway and I was with my girlfriend so I couldn’t let that happen. Caught up with the GTO after a while and the tach wasn’t even straining. Blew by him like he was standing still and the wind from passing lifted the hood and the radiator support bracket which dropped it into the fan. Ooops. Impress the girlfriend…..not. And the other GTO cruises by. Yup young and dumb. Lived to talk about it. I couldn’t keep axle bearings in it or tires on it. Ended up selling it for $800.


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## Bopman (7 mo ago)

ppurfield001 said:


> I'm trying to figure out this gear ratio thing, Rukee. If I am going 70 mph on the highway, my 400 cubic inch engine is at about 3200 RPMs. Is that similar to your story above and, if you can venture a guess, what kind of gears am I running?


Just came back from a cruise today on a parkway with my wife following me at 70 mph tach was at about 3200 and gear ratio is 3.42 in 72 lemans. Hope this helps.


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## Bopman (7 mo ago)

Bopman said:


> Just came back from a cruise today on a parkway with my wife following me at 70 mph tach was at about 3200 and gear ratio is 3.42 in 72 lemans. Hope this helps.


My guess is either 336 or 342 not a whole lot of difference there.


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## DONNY (4 mo ago)

Eric Animal said:


> My 67 has 2.93 gears....doggy off the line great top end..by todays standards it still feels like it needs another gear (TH400)....I was thinking of a set of 3.73 with a 4spd auto..200r4 can be built to take some torque. It is also an easy swap ....shorter yoke on the drive shaft..and a kit to adapt the his/hers.............Cool Thread


with 2.93 u need another gear on the hiway lol


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