# Any Advice? - swapping TH200R4 for TH400 - 69 GTO



## Heatwave (Nov 30, 2014)

I have a nice 69 GTO convertible. Its fully restored but it does not have a matching #s engine although, it is a correct 400 with 69 Q-jet and 69 Heads. Its got the original TH400 tranny but somewhere in its life it had the stock rear diff increased to 3.9 ratio (unfortunately its open). As you can imagine, running on the highway is not alot of fun as the rpms are over 3k.

I use it as a cruiser and no plans for track time. I've done alittle homework and it sounds like a well built TH200R4 would be a nice combination with the 3.9 rear. It would maintain the sharp acceleration while bringing the rpms down on the highway with the OD. I would be interested in any advice as well as a shop recommendation for Northern New Jersey. 

Thanks for the advice.


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## PontiacJim (Dec 29, 2012)

Buy this book, it'll give you the info you need to know. Cliffs High Performance Quadrajets :: Qjet Carburetor Rebuilding, Bushing Kits and Parts


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## Nightshade 68 HO (Mar 11, 2014)

Good choice on the trans. I had one in my monte ss and it sank the cruisng rpm with my 3.42 to around 2000 at 65 plus....(our monte tachs were pretty inaccurate with msd ignition).

I swapped out a 350 trans in my car, as mine was an 84. I needed a different crossmember, but I was able to keep the same driveshaft. ( I am not sure of any length diffs with a 400 trans. The trans does NOT use a kickdown cable, it uses a TV cable that requires a special bracket for your carb as this TV cable dictates fluid pressure on the trans and shift firmness. With the 2.75 first gear and .62 od (if I recall) your 3.90 rear will be great on the highway down to about 2400 rpms at 70 mph plus...if you have a lock up convertor, which these transmissions have (make sure you get the right lock up kit).


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## WhittP (Jun 19, 2013)

I did this swap on my 67 GTO convertible. No floor pan cutting but the drive shaft had to be cut down a couple of inches. Not a big deal. My car has a 3.55 rear and this tranny brought the cruising rpms down from 3400 to 2400 just like Nightshade says. You'll want to make sure you get the proper TV cable kit since adjustment and linkage geometry is crucial for proper function. Not a big expense. You'll also want to pick up a transmission/oil pressure gauge to get the set up 100% correct. They are cheap and the hook up is super easy. All in all, it's been the best mod I've done to my car I think you're making a great choice.


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## Heatwave (Nov 30, 2014)

Thx for the feedback. I can get a 200R4 stage 1 (500hp + 2yr warranty) with complete conversion kit (TV cable, carb bracket, cooler, cross member, dip stick, speedo gear etc) for about $1900 including shipping to the shop. 

Labor estimate for the install is $1000. I also looked at installing a shifter kit so the detents, brackets and decal inside the car match the 4sp auto $90. Do these prices seem reasonable. Anything I'm missing?


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## oldskool (Apr 26, 2015)

*Or*

I'm old school. So, I prefer the original TH400. Swap the gears to 3.36 or 3.55.

GM 8 2" Bop 10 Bolt Posi Ring Pinion Gear Package 3 55 Buick Olds Pontiac | eBay

New Auburn Posi Unit and Motive Gears 3:36 - PY Online Forums

Buy a Continental brand torque converter for your app. They'll provide very little slip at cruise. But at the hit of the throttle they will flash to a higher stall speed for better launch.

Products

The same guy who wrote the OD trans book, just mentioned, also recommends and sells Continental converters. 

PY Online Forums - View Single Post - Picking Torque Converter

Doing it this way keeps it looking more original. There is nothing original about an OD 4-speed automatic trans in a '69 GTO. 

Also, problems with that TV cable that was mentioned can totally fry a 200-4R

Art Carr's 700r4 tv cable adjustment guide from CPTtransmission.com


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## geeteeohguy (Feb 2, 2008)

I'm with Oldskool here. A 3.90 peg leg is a useless gear to run. Anywhere. Me, I'd slip in some 3.36 gears and drive the car. Direct bolt-in, total cost if you have it done, plus gears, under $1200. IF it still revs too high for your liking, install the TH200. Plan B for me would be to find a used rear end assembly with better gears and bolt it in. Anywhere from free to $500. I bolted a free 2.56 posi into my '67 GTO about 5 years ago and love getting 21MPG at 75-80 mph....running cool and smooth all day long. My car used to run 70 mph at 3,000 rpm. Now it runs a tick over 90mph at 3,000. If you have the cash, the TH200 is a really slick set-up. But still, I'd get rid of the 3.90 rear gear and install a 3.36 gear. AND have the overdrive.


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## Eric Animal (Oct 28, 2007)

Just make sure to keep the original parts....I have a 3.73 rear in my 67 GTO...a 4L80e transmission... OD is .75 to 1. , with 27 inch rear tires 85 mph is only about 2600 RPM....


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## Heatwave (Nov 30, 2014)

Thanks for the feedback. I've decided to go with 200-4R upgraded to stage 1 (upto 550hp), with the conversion kit:
Rochester Linkage
TV Cable
Speedometer (calibrated for 26" tires plus 3.90 rear diff)
Mount
Dust Cover
Dipstick & Tube
Throttle Bracket
Torque Converter Bolts
Lock Up Wiring Kit
Hayden Cooler
2 Can Cooler Flush 

They had a sale yesterday and I got the entire package for $1450 plus shipping to my installer's shop. The stock TH400 cross member can be relocated and used with the 200 4R according to Transdepot.

I also order AMES 1969 GTO shifter conversion kit ($90) to have the shifter detents and decal match the new gear positions.

I also got the rear diff posi carrier ($350) with install kit (bearings/shims - $90) to convert my open 3.90 into a posi. Based on the feedback so far the 3.90 rear is an excellent match for the 200-4R for both take off and highway.

It'll take 2.5 weeks to have Transdepot build the 200 as they have a log of 70 transmissions to build and get 7-10 new orders each day. Includes 2 yr unlimited mileage warranty.

Shop estimated $700 labor for the tranny swap and setup and $500 for the rear posi labor install.

I'll store the TH400 away should I ever go back or a future owner want's to go back.

All-in, the 4sp auto transmission with posi upgrade will cost me about $3600 all in. I hope to have some results to post in about a month.


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## geeteeohguy (Feb 2, 2008)

Converting the 3.90 to a posi was an excellent idea.....with the combination of a stiffer first gear and the overdrive, you'll end up with a whole new car. It'll be a lot faster off the line and get much better fuel mileage on the road. Total win. Good luck with the install. I can't for the life of me imagine anyone ordering an open 3.90 gear.....I could never hook up an old bone stock '65 GTO I once had with a peg-leg 3.23 and 60 series tires. These cars absolutely need a limited slip rear end, IMO.


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## Heatwave (Nov 30, 2014)

I agree. I can't imagine what the guy was thinking that went into the rear of this GTO and changed the gearing from the stock open 3.23 (according to the order sheet on the car) to a 3.90 AND THEN also made the decision to leave it open.


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## Heatwave (Nov 30, 2014)

Quick update on my 1969 GTO 200R4 transmission conversion and posi differential project. Ran into a small issue. The original Pontiac 400 flex plate does not have matching bolt holes for the 200R4. I needed to order a new flex plate that mates the 400 engine and GM15 Torque converter on the 200R4. 

I also needed a new yoke (which I anticipated). The factory setup had a 32 spline 5.5" (3.75" internal machining) with a 1310 U-joint. The 200R4 has 27 splines and was overall about 1.25 shorter than the TH400. I needed to order a 27 spline yoke that was 1.00-1.25" longer. I ordered a 6.75 (5.00" internal machining) with internal snap rings. 

The new flex plate and yoke should get me back in business. Good news is that the TH400 transmission support will work with the 200R4. 

I'm sure there'll be more surprises but for $200, the flex plate and yoke weren't too bad of a surprise.... so far anyways.


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## Pinion head (Jan 3, 2015)

Congrats on the headway on your '69, should work out well. In reading, found it odd that your previous driveshaft had a T400 yoke with a spicer 1310 u-joint. The original driveshaft would have had the larger 3R ujoint, same as the one mating to the pinion flange on the Pontiac 8.2 10 bolt rear. Btw, did you need a longer driveshaft with the 200R4?


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## Heatwave (Nov 30, 2014)

Hmmmmm. I went by the mechanic that said it was a 1310 u-joint although I didn't look at it myself. The original driveshaft will work although I need a 1" longer yoke to accommodate the fact that the 200 is overall shorter than the 400 I had.

I got another little surprise today. The 3.90 gears I thought I had in the diff are actually 3.55. I've decided I'm going to replace the 3.55 (sell it) and replace it. I'm a little torn on whether I should go with 3.73 or 3.90 but I'm leaning towards the 3.90 with the 200 R4 ratios. I would be at 2400 on the highway at 70mph with the 200R4, 26" tires and a 3.90 rear which sounds good to me. Any thoughts would be welcome.



Pinion head said:


> Congrats on the headway on your '69, should work out well. In reading, found it odd that your previous driveshaft had a T400 yoke with a spicer 1310 u-joint. The original driveshaft would have had the larger 3R ujoint, same as the one mating to the pinion flange on the Pontiac 8.2 10 bolt rear. Btw, did you need a longer driveshaft with the 200R4?


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## geeteeohguy (Feb 2, 2008)

My thoughts? Keep the 3.55 gear. It's perfect for what you are doing. 2400 at 70 mph is 'ok', but 2400 rpm at 80mph is much better. Combined with your stiffer first gear in the TH200, your 3.55's will be excellent in every application. I would leave them be.


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## Heatwave (Nov 30, 2014)

According to the Transmission shop and their software, a '69 GTO with a 400, 26" tires and a 200 R4 should be run with a 3.55 rear at a bare minimum. Preferably above 3.55.


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## ALKYGTO (Mar 29, 2010)

Agree with GeeTee....keep the 3:55's at least until you try them out. If not happy then consider the swap to a deeper gear. I think you'll be happy overall with the 3:55's and honestly the deeper gear may not make the car any quicker....


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## Heatwave (Nov 30, 2014)

Thanks for the responses. I am curious why I wouldn't feel greater acceleration with the a 3.73 or 3.90 vs the 3.55. That's 2 votes for sticking with my 3.55. Is the primary thinking that the faster acceleration is negligible but the reduction of rpms on the highway will be a bigger benefit???



ALKYGTO said:


> Agree with GeeTee....keep the 3:55's at least until you try them out. If not happy then consider the swap to a deeper gear. I think you'll be happy overall with the 3:55's and honestly the deeper gear may not make the car any quicker....


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## BearGFR (Aug 25, 2008)

Heatwave said:


> Thanks for the responses. I am curious why I wouldn't feel greater acceleration with the a 3.73 or 3.90 vs the 3.55.


Two words: Pontiac Torque. This ain't no chevy you're dealing with here. When I first got my 69 running, it was only drivable if I kept my foot out of it. I had a shop locally custom build me a torque converter for the car and I told them I wanted a 3000-3200 rpm stall. I took great pains to point out to them what they were building for, even gave them a copy of my dyno sheet. They didn't pay attention (or thought they knew better than I did) and built me a 'chevy' converter. Result? As soon as I hit the throttle the engine was instantly well over 4000 rpm. I took it back to them and wanted it fixed. At first they wanted to argue, but when I demonstrated to them that I could hold the car with the brakes, apply throttle, and reach 5000 rpm before the car overpowered the brakes and started turning the tires _anyway_, I got their attention (and a new converter). Oh, and my '69 has 3.50 gears (Moser 9-inch rear).

Yes, you might get slightly more 'seat of the pants' feel with more gear than 3.55, but with 3.70's or more you're not going to like driving it at freeway speeds for more than a few minutes. Plus it's going to put more wear on the engine. Heck, even with 3.50's and slightly taller than stock drag radials, at 70 mph I'm turning 3100-3200 rpm. I'm kind of in a box with my car because if I go with a taller gear then at 70mph my converter is still going to be slipping (and generating heat). 

Point is, be honest with yourself. How are you going to be driving the car? If it's going to be spending much time at freeway speeds, then I'd stay with 3.23's or LESS. If it's mostly in town, occasional racing - minimum of highway use then maybe you can get by with more gear and be fine --- but be honest.

Getting both (acceleration and freeway capability) is possible but it's not cheap. You're talking some sort of overdrive and a lock-up converter. Something like a Gear Vendors overdrive, or a later model transmission with overdrive built in (or a 5-6 seed manual). But it's not a trivial exercise to install one of those because it almost always involves enlarging the tunnel and modifying the floor, plus your 'garden variety' overdrive trans is not going to survive long behind a strong Pontiac.

Bear


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## Heatwave (Nov 30, 2014)

The diff gear ratio I've been debating would be behind a 200R4 4sp Auto already being installed. Therefore it will have a .67 ratio in 4th gear vs the the 1.00 in the TH400 3rd gear combined with either a 3.55 or 3.73.

I've decided to follow the recommendations here at the forum. I'm sticking with my 3.55 upgraded with a posi carrier. The gears were in great condition so reinstalling with the posi was the best alternative. it was a coin toss on the 3.73 vs 3.55. Minor +s and -s to both behind a 200R4.

The recommendations from the forum plus the fact that I have the 3.55 already made it a relatively easy call. Thanks to all. More updates to follow once the new flex plate and extended yoke arrive.



BearGFR said:


> Two words: Pontiac Torque. This ain't no chevy you're dealing with here. When I first got my 69 running, it was only drivable if I kept my foot out of it. I had a shop locally custom build me a torque converter for the car and I told them I wanted a 3000-3200 rpm stall. I took great pains to point out to them what they were building for, even gave them a copy of my dyno sheet. They didn't pay attention (or thought they knew better than I did) and built me a 'chevy' converter. Result? As soon as I hit the throttle the engine was instantly well over 4000 rpm. I took it back to them and wanted it fixed. At first they wanted to argue, but when I demonstrated to them that I could hold the car with the brakes, apply throttle, and reach 5000 rpm before the car overpowered the brakes and started turning the tires _anyway_, I got their attention (and a new converter). Oh, and my '69 has 3.50 gears (Moser 9-inch rear).
> 
> Yes, you might get slightly more 'seat of the pants' feel with more gear than 3.55, but with 3.70's or more you're not going to like driving it at freeway speeds for more than a few minutes. Plus it's going to put more wear on the engine. Heck, even with 3.50's and slightly taller than stock drag radials, at 70 mph I'm turning 3100-3200 rpm. I'm kind of in a box with my car because if I go with a taller gear then at 70mph my converter is still going to be slipping (and generating heat).
> 
> ...


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## PontiacJim (Dec 29, 2012)

I agree with what has already been stated. Pontiac uses torque, not rpm, to get the job done. Here is a list of automatic ratio's and maybe a little extra info for you. Race-Track.com

If you play around with one of the many on-line gear ratio/rpm/speed calculators, you will see the differences in the gearing when using the TH400 with 3.90 gears and the 200R4 with 3.55's. I played around with one calculator using a 26" tall tire and first gear ratio's only. The TH400 with 3.90 gears puts your engine at 5,000 RPM's @ 40 MPH. The 200R4 with 26" tire and 3.55 gears put the engine at 5028 RPM's @40 MPH. So, you can see the fairly close RPM's at the same speeds. You lose almost nothing and acceleration should be close to the same. It will be in the OD range where you will truly benefit. The 200R4 with what is listed as .67 in OD shows that at 70 MPH your engine will be turning 2152 RPM's (you have a lock up converter?) which is perfect for highway cruising and reasonable gas mileage.:thumbsup:


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## Heatwave (Nov 30, 2014)

PontiacJim said:


> I agree with what has already been stated. Pontiac uses torque, not rpm, to get the job done. Here is a list of automatic ratio's and maybe a little extra info for you. Race-Track.com
> 
> If you play around with one of the many on-line gear ratio/rpm/speed calculators, you will see the differences in the gearing when using the TH400 with 3.90 gears and the 200R4 with 3.55's. I played around with one calculator using a 26" tall tire and first gear ratio's only. The TH400 with 3.90 gears puts your engine at 5,000 RPM's @ 40 MPH. The 200R4 with 26" tire and 3.55 gears put the engine at 5028 RPM's @40 MPH. So, you can see the fairly close RPM's at the same speeds. You lose almost nothing and acceleration should be close to the same. It will be in the OD range where you will truly benefit. The 200R4 with what is listed as .67 in OD shows that at 70 MPH your engine will be turning 2152 RPM's (you have a lock up converter?) which is perfect for highway cruising and reasonable gas mileage.:thumbsup:


Thanks for the input. Just to clarify I mistakenly thought I had a 3.90 in my GTO with my stock TH400. As it turned out I had a 3.55 ratio. So my comparison is between my current TH400 with 3.55 rear and a TH200R4 with a 3.55 rear.

The ratios for the TH400 are 
1st - 2.48	
2nd - 1.48	
3rd - 1.00

The ratios for the TH200R4 are:
1st - 2.74	
2nd - 1.57	
3rd - 1.00	
4th - .67

My take away from these ratios with the same rear gear ratio (3.55) and the same 26" tires is that:
- 1st gear should pull stronger with the 200R4 (2.74) vs TH400 (2.48)
- 70mph with the 200R4 in OD should be at 2150rpms
- 70mph with the TH400 in 3rd gear is at 3200rpms

Advantage to the TH200R4 over the TH400 in terms of acceleration as well as lower highway rpms. Am I looking at this correctly??


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## ALKYGTO (Mar 29, 2010)

:thumbsup:


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## Red1970GTO (Jun 25, 2011)

*Th200*

:lurk:


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## PontiacJim (Dec 29, 2012)

BINGO! By George I think he's got it! :grouphug: By installing taller tires, you can actually play around a bit with the RPM/MPH range. Taller tires will drop the RPM's at the given MPH's listed. 

You might think that you now have "top end unlimited," but you don't. It takes a lot more HP to overcome the frontal pressure/drag of the car - not to mention your suspension/car is not set-up for such high speed MPH runs even if you could. Air gets under the car and lifts, making your steering feel exceptionally light because you are riding on a cushion of air and not your suspension any more. Go into a tight curve at speed, and you may find the laws of physics taking place as your car points straight while you turn your steering wheel & tires all the way_ in the direction you would have liked to have gone._ You only have to experience that once and be able to pull through the curve and live to know better than do that again.....at least in a curve.:lol: BTW, always good to keep in the trunk some extra oil, trans fluid, anti-freeze, and.....an extra pair of underwear.:blush2:


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## Heatwave (Nov 30, 2014)

Ran into an interesting new snag. Curious on any insight out there. 

As you've already read, I have an open rear with 3.55 factory gears. I assume the gears are factory original as they are stamped 1969 - 3.55. 

So I order a posi carrier designed for an 8.2 BOP 10 bolt differential for a 1969 Pontiac rear end. The posi arrives and the splines are fine for the axles and all is good EXCEPT the holes in the posi are machined for 3/8s bolts. My plan is to reuse the 3.55 gear set but my ring gear has 7/16s holes for LH bolts. I believe the ring gears for a 1969 GTO would have had 3/8 holes for RH bolts.

All my research suggests that my 1969 GTO should have 3/8 RH bolts from the factory yet the rear looks original.

Anyways, the fix is relatively simple by having the posi holes machined for 7/16" bolts. The dealer I bought the Posi from is drilling out the bolt holes to 7/16s at no charge. 

Anyone have any idea why the holes and thread pattern would be different on my factory setup. Were they just pulling from different parts bins in 1969????


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## PontiacJim (Dec 29, 2012)

From a quick search, and being no expert on the subject, it would appear that the 7/16" bolts are used on the 8.5" rear while the 3/8" bolts are used on the 8.2" rear. I don't think the factory stamped "1969 - 3.55" on 'em. That sounds like an aftermarket set of gears in my opinion. So, you may actually have an 8.5 rear?


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## Heatwave (Nov 30, 2014)

PontiacJim said:


> From a quick search, and being no expert on the subject, it would appear that the 7/16" bolts are used on the 8.5" rear while the 3/8" bolts are used on the 8.2" rear. I don't think the factory stamped "1969 - 3.55" on 'em. That sounds like an aftermarket set of gears in my opinion. So, you may actually have an 8.5 rear?


Its a possibility except the splines on the axles with an 8.5 should not fit on the posi I have that was designed for an 8.2. I have already tested the posi and the axles fit properly on the carrier.

Anyone know if there was ever an 8.2 differential that used 7/16 bolts on the gear set?

I believe only the BOP 8.2 10bolt diff had the side cutouts on the cover (mine is chromed). Here's some pics


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## geeteeohguy (Feb 2, 2008)

Heatwave, you need to talk to pinionhead, on this forum. He wrote the book on GM rear ends. He is The Man. That said, you are dead right with your200R4 calculations. It will really wake up your car, as well as lower your engine wear and gas consumption. You'll want to drive it all the time. What Jim said about 'unlimited top end' is true. My '67 would be at 158 mph at 5200 rpm. But it won't pull redline in top gear with the 2.56 rear screw. The fastest I've been in this car was a tick over 130mph, and that's where the wall is for these cars. The front end gets light and twitchy, and the car starts to float. Very, very unsettling. While I was sitting there at 130-ish, (on a closed track, of course!) my buddy in his 455 equipped, dual quadrajet, 4 speed, 2.41 geared '74 Firebird had to shift down into THIRD gear to pull around me. He couldn't do it in 4th. Then he just slowly walked away from me. With ground effects, excellent tires, air dams, etc, his Firebird was planted solid at 145mph, and felt safer than my GTO at 115 or so. Aerodynamics really come into play at high speeds!!


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## Pinion head (Jan 3, 2015)

Heatwave said:


> Ran into an interesting new snag. Curious on any insight out there.
> 
> As you've already read, I have an open rear with 3.55 factory gears. I assume the gears are factory original as they are stamped 1969 - 3.55.
> 
> ...


Heatwave, late in '69 production, the Pontiac 8.2 10 bolt carriers and ring gears were enlarged 1/16" . Ring gear bolts went from 3/8" RH thread, to 7/16" LH thread. Several times over the years, Ive had to make thin brass bushings for the opposite problem, late style 8.2 Pontiac 10 bolt carrier with larger diam ring gear bolt holes being mated to an early style (and Richmond) 8.2 Pontiac gears. The only '69 Pontiac 8.2 10 bolts I've ever ran across the 7/16" lh thread ring gear in came out of late '69 Firebirds. If you have a '69 usage Pontiac A body rear that this ring and pinion came out of, I'd love to get some pics of the stamped axle tube codes, as well as know if the rear came with tapered bearing axle bearings (have an external seal). That is the other "late '69" revision.

In your instance, either have to have the ring ger flange holes opened up on the carrier, or in the case of original 4 pinion safe-t-track carriers can occasionally get someone to swap tto the correct late style 4pinion STT carrier, have managed to do the latter several times.


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## Heatwave (Nov 30, 2014)

Pinion head said:


> Heatwave, late in '69 production, the Pontiac 8.2 10 bolt carriers and ring gears were enlarged 1/16" . Ring gear bolts went from 3/8" RH thread, to 7/16" LH thread. Several times over the years, Ive had to make thin brass bushings for the opposite problem, late style 8.2 Pontiac 10 bolt carrier with larger diam ring gear bolt holes being mated to an early style (and Richmond) 8.2 Pontiac gears. The only '69 Pontiac 8.2 10 bolts I've ever ran across the 7/16" lh thread ring gear in came out of late '69 Firebirds. If you have a '69 usage Pontiac A body rear that this ring and pinion came out of, I'd love to get some pics of the stamped axle tube codes, as well as know if the rear came with tapered bearing axle bearings (have an external seal). That is the other "late '69" revision.
> 
> In your instance, either have to have the ring ger flange holes opened up on the carrier, or in the case of original 4 pinion safe-t-track carriers can occasionally get someone to swap tto the correct late style 4pinion STT carrier, have managed to do the latter several times.


The car is at the shop so I have limitations on my pics for now. Below is a pic from the passenger side rib of the diff viewed from the rear. The casting # looks like either 9798100 or possibly 9789100. Does that casting # help identify the diff? 

If it helps, the car was built in the 2nd week of April 1969 in Baltimore as a GTO Convertible. PHS shows it was built with an open diff.

I've also read that Buick 8.2 10bolt diffs in 1969 had 7/16 LH bolts. Any info off the casting # would be appreciated. My solution was to have the bolt holes on the posi carrier machined to accommodate a 7/16 LH bolt. Since the ring and pinion operated fine before dis-assembly, it should solve the issue of upgrading to a posi. The gears ran great with no real whine or clunking as an open diff with my 3.55 gears.


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## Pinion head (Jan 3, 2015)

Heatwave, the 9799100 center hsg casting number is one of at least 2 different gray iron casting numbers used on '69 gray iron Pontiac A and GP 8.2 10 bolts. Would love to see a high resolution pic of the stamped axle tube numbers and two letter code, as well as pic of the casting date on the center housing, and the date stamped into the ring gear. With the single track carrier coming out, would also really be nice to know if the axles have sealed axle bearings, or if tapered axle bearings with external seal. I have been trying to nail down changeover timeline for many years. Nearly 20 years ago, I parted a really solid gold '69 LeMans 2 door hardtop. It's body build was extremely late, 08A out of Arlington plant. The gold LeMans is the only A -body I've ever ran across that was dated so late in a production year. Of major interest when disassembling that particular '69, it had its original sealed axle bearing Pontiac 8.2 rearend, not the redesigned tapered axle bearing 8.2 Pontiac rear.

On the '68-70 BUICK 8.2 10 bolts, they do have 7/16" ring gear bolts. Problem is, the '68-70 BUICK 8.2's are their own animal, they use nothing from an earThe redesigned for '68 Buick 8.2 10 bolt rears used specific cast housings, take different carriers, and different design ring and pinions that don't interchange with 8.2 Pontiacs. Even the axles are '68-70 BUICK 8.2 only due to the pitch of the axle splines. Have had several of these Buick only 10 bolts and have rebuilt a few more. 

The evolution of all the non Chevy 10 bolt rears, i.e., the difference in the Pontiac 8.2 rears, along with the totally different '67-70 type "O" Olds 10 bolts, and the '68-70 BUICK 8.2 10 bolts is why I don't use the term "BOP 8.2" it's just a poor term to describe rearends from this era.


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## Heatwave (Nov 30, 2014)

Pinion head said:


> Heatwave, the 9799100 center hsg casting number is one of at least 2 different gray iron casting numbers used on '69 gray iron Pontiac A and GP 8.2 10 bolts. Would love to see a high resolution pic of the stamped axle tube numbers and two letter code, as well as pic of the casting date on the center housing, and the date stamped into the ring gear. With the single track carrier coming out, would also really be nice to know if the axles have sealed axle bearings, or if tapered axle bearings with external seal. I have been trying to nail down changeover timeline for many years. Nearly 20 years ago, I parted a really solid gold '69 LeMans 2 door hardtop. It's body build was extremely late, 08A out of Arlington plant. The gold LeMans is the only A -body I've ever ran across that was dated so late in a production year. Of major interest when disassembling that particular '69, it had its original sealed axle bearing Pontiac 8.2 rearend, not the redesigned tapered axle bearing 8.2 Pontiac rear.
> 
> On the '68-70 BUICK 8.2 10 bolts, they do have 7/16" ring gear bolts. Problem is, the '68-70 BUICK 8.2's are their own animal, they use nothing from an earThe redesigned for '68 Buick 8.2 10 bolt rears used specific cast housings, take different carriers, and different design ring and pinions that don't interchange with 8.2 Pontiacs. Even the axles are '68-70 BUICK 8.2 only due to the pitch of the axle splines. Have had several of these Buick only 10 bolts and have rebuilt a few more.
> 
> The evolution of all the non Chevy 10 bolt rears, i.e., the difference in the Pontiac 8.2 rears, along with the totally different '67-70 type "O" Olds 10 bolts, and the '68-70 BUICK 8.2 10 bolts is why I don't use the term "BOP 8.2" it's just a poor term to describe rearends from this era.


I now understand why it makes no sense to refer to a BOP 8.2 10bolt rear as is there was only one design. It sound like there are multiple "BOP" 8.2 10bolts from '68-70.

Would my gray casting # with 7/16 ring bolts "qualify" as a stronger rear than those with 3/8s ring bolts??

I'll try to get more pics of the axle codes and pics of the housing casting date and ring gear to post. My new posi machined for 7/16 bolts will be arriving at the shop on Monday. I'll also try to get more info on the axle bearings.

More to follow.


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## Pinion head (Jan 3, 2015)

The problem with the "BOP" moniker is it is meant to inclusive, where as '67-70 Olds A bodies received the Type "O" Olds 10 bolts, '68-70 Buick A bodys received the revised BUICK 8.2 10 bolts, and Pontiac from '64-72 received theevoke evolving 8.2 Pontiac 10 bolt. There was no sharing amongst the three divisions from '68-72. A few Buick and Olds '68-70 Abodys, nearly all from Canada, received the first McKinnon 12 bolts. 

On the gray iron 8.2's, the upgrade to tapered axle bearings was a major improvement. I've yet to run across a sheared 3/8" ring gear bolt, 12 bolts used that size as well. Looking fwd to pics, am always trying to narrow original uses down.


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## Heatwave (Nov 30, 2014)

Here's some additional information on my '69 GTO rear differential. I have some doubts that its original to my car. I could find no casting #s on the axle tubes as the tubes have been painted multiple times over the years. There are clear white painted references *"#5 '69 3.55 NP"* on the driver tube and "OPEN" on the passenger tube. The '69 3.55 NP is a clear reference to 1969 non-posi 3.55 differential. I have no idea what the #5 means. 

I looked very closely with a bright light and could find no other casting marks on the tubes or diff casing. I suspect the white painted references were placed there by a salvage operation if I had to guess.

The axles do have tapered bearings and the differential is definitely an 8.2 with 10bolt cover and 10bolt interior.

The open carrier that was in the case when I bought the car has a casting # "4847" where the #7 is larger than the 484 and a "19" casting on the opposite side of the open carrier. The flat side of the carrier has a casting # of "230" and a large "C".

The ring gear has "39-11GM 69L" engraving.

I forgot to get a picture of the pinion. The diff is going back together today with the new posi carrier and the original gear set.

Let me know if these codes help better identify the source of this rear axle setup.


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## Pinion head (Jan 3, 2015)

Thanks for looking at the axle tubes. Glad to hear its a tapered axle bearing 8.2, as well. 

Will get out and ck and measure some '69 and 70 8.2 housings, where the ID codes are stamped. Will try and get some pics to fwd. On the GM gears, they usually have a month and date stamp on the side of ring gear near the part number, as well as on the face of the pinion. I have seen the dates on these as far as 10 months before the assembled date on the axle tube. It just depends on the model year and how popular the gear set was.


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## Heatwave (Nov 30, 2014)

Pinion head said:


> Thanks for looking at the axle tubes. Glad to hear its a tapered axle bearing 8.2, as well.
> 
> Will get out and ck and measure some '69 and 70 8.2 housings, where the ID codes are stamped. Will try and get some pics to fwd. On the GM gears, they usually have a month and date stamp on the side of ring gear near the part number, as well as on the face of the pinion. I have seen the dates on these as far as 10 months before the assembled date on the axle tube. It just depends on the model year and how popular the gear set was.


Is this # stamped in the gear ring the part # "39-11GM 69L"? I didn't see any other stamping on the gear ring. Do the open carrier stampings provide any addition information?


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## kilkm68 (May 5, 2011)

I have a 200 4r stage 3, rated for 1000 HP built by Extreme Automatics in Cincinnati, in my '68 behind a BUTLER 474 with a Chevy 12 bolt rear end with 373 gears. With 28 inch Goodyear Eagle drag radials, at 70 mph and the converter locked up, I'm turning about 2100 rpms. At 60 mph about 1800. Last month on the hotrod power tour I averaged almost 18 mpg, and that's with a Holley 770 cfm street avenger carb and putting my foot in it a few times. I love this transmission. It jumps off the line hard enough to snap your neck, shifts at red line fast as a motorcycle, yet driven on the highway in overdrive with the converter locked will yield decent fuel economy. I was also told that a TH 400 will consume about 75 HP but a 200 4r will only consume about 35. I don't know how true that is but it's an additional bonus if it is. I think these Tranny's are the best of both worlds, excellent choice!


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## Heatwave (Nov 30, 2014)

kilkm68 said:


> I have a 200 4r stage 3, rated for 1000 HP built by Extreme Automatics in Cincinnati, in my '68 behind a BUTLER 474 with a Chevy 12 bolt rear end with 373 gears. With 28 inch Goodyear Eagle drag radials, at 70 mph and the converter locked up, I'm turning about 2100 rpms. At 60 mph about 1800. Last month on the hotrod power tour I averaged almost 18 mpg, and that's with a Holley 770 cfm street avenger carb and putting my foot in it a few times. I love this transmission. It jumps off the line hard enough to snap your neck, shifts at red line fast as a motorcycle, yet driven on the highway in overdrive with the converter locked will yield decent fuel economy. I was also told that a TH 400 will consume about 75 HP but a 200 4r will only consume about 35. I don't know how true that is but it's an additional bonus if it is. I think these Tranny's are the best of both worlds, excellent choice!


Terrific endorsement of the 200R4. My setup will be "more down to earth" and closer to stock but I hope to have as strong an endorsement as yours once everything is back together. I needed some machining on both the posi carrier I had installed as well as the longer yoke I needed for the 200R4. Also needed a different flex plate to mate my 200R4 to my pontiac 400. Each caused a slight setback but I'm back on track

I hope to have results to share soon.


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## Heatwave (Nov 30, 2014)

Another quick update. Needed to get a Shiftworks "Neutral Safety/Backup Light Switch Re-Location to Shifter Conversion". This switch is needed if you want the safety of not allowing the car to be started "in gear". It also will allow the backup lights to be energized when the car is in reverse. With the switch installed in the center console, wiring needs to be run under the carpet to the steering column to tap into the backup lights and ignition.

Just another part of the install that needs to be considered when converting from a stock TH400 to a 200R4.


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## Heatwave (Nov 30, 2014)

Latest update and summary of my open to posi diff conversion and swap out of my TH400 for a 200R4 transmission project. The transmission is a 200R4 stage 1 upgrade (Up to 550HP) including an 1800-2100 Stall Torque Converter from TransDepot.

I'll get to the conclusion first for those not interested in the details. This combination is excellent and I highly recommend both conversions. The car runs terrific as its now setup with a 4sp OD 200R4 replacing my stock, 3sp - 1969 TH400. Shifts are strong. Downshifts are outstanding, even dropping from 4th to 2nd quickly when needed without limited delay. No lugging when just cruising around town. Hit the throttle hard and EVERYONE near you will hear it. I have a new 2.5 inch stainless exhaust with (new) stock D-Port R/A & HO Exhaust Manifolds. My exhaust is from PYPES NDGA20S23 and I used PYPES 2.5" polished stainless exhaust tips NEVT42 that replicate the factory look straight out the back only they are much larger.

*THE GOOD*

Turn the AC off, put my foot firmly on the brake on a nice deserted straight road, take the RPMs up to 2500+ and a burn out will start easily. Put the pedal to the floor while releasing the brake and I can do a burn out for almost as long as I want. 2 nice black stripes down the road with the new posi diff.

For a refresher, I have the original 3.55 rear gears upgraded to a posi with the 200R4 (2.74/1.57/1.00/0.67) which has a stouter 1st gear than the original TH400 (2.48/1.48/1.00). No changes to the motor but it feels so much stronger and yet so much more comfortable both in town and on the highway. 

I upgraded the rear diff with a posi. This required some interesting modification as I have a 10 bolt Pontiac rear but the carrier bolts are LH 7/16s instead of the expected RH 3/8 bolts. The holes needed to be bored out to accommodate the larger bolts and the recesses needed to be milled larger so the socket would fit over the bolt head. Otherwise the rear came out as planned and there's no whine or sloppiness. Just terrific power to both wheels which is a whole lot nicer than the former peg leg.

60mph at 18-1900rpms. 70 at 2200. 80 at 2500 VERSUS 3300 at 70 with the TH400. Its just a joy to ride around in now. It drops a gear and rips whenever I need it to, while cruising on the highway with comfort, power and almost double the fuel economy. Enough power to accelerate dramatically from almost any speed. Not enough mileage yet for a fuel economy calculation but at these RPMs it should be substantially improved. Latest estimates are about 18-19mg vs the previous 10-11 mpg with the TH400.

While its not as dramatic as my 540hp Audi for comparison, its just as exciting with alot more sound to go with it. And with the top down it feels faster than the Audi even though its definitely not.

The speedo gear from Transdepot was perfect. I was somewhat shocked to see that my dash speedo reads almost exactly the same for every speed from 10-80 as on my phone GPS speedometer.

This is the way a 1969 GTO should feel even though I know a few purists are puking by now.

*THE LESS THAN GOOD*

The project is not plug and play. If you have the right gear set (3.55 feels great to me) and a posi to start with, you'll be way ahead in the project.

The tranny swap takes some adjustments that you should be prepared for:

- you may need a new flex plate. My original 400 flex plate did not have matching holes for the 200R4. This may be an additional expense to plan on.

- If you have a stock TH400, your drive shaft should be fine but you'll need to get a longer yoke. I needed about an additional 3/4inch long yoke than the one on the TH400. I bought the longer yoke from FastShafts. Let them know what you need and they should be able to help you. The stock cross member will work just fine, so you'll save money not buying a new one to fit the 200R4 on a 1969 GTO.

- You'll need to install the tranny cooler up front and the original TH400 cooler lines will not be long enough. Fortunately the Trans kit I order included longer cooling lines that worked great.

- You'll need to cut the trans dip stick to fit the GTO. About an inch off the tube that my kit came with. You'll need to adjust the dip stick accordingly.

- Installing the TV cable is key to the success of the conversion. The bracket my kit came with just wasn't going to work. Fortunately my mechanic had done numerous conversions and was able to make a very attractive chrome bracket that looks great with my 1969 GTO Rochester carb and edlebrock intake. It neatly organizes both the TV cable and the throttle cable and looks like it came from the factory. It did however require moving the coil to the passenger side of the block. No big deal as all wires were long enough.

- Adjusting the TV cable is a challenge. My mechanic had it set abit too strong with shifts that were too jarring for my tastes. I marked his setting with tape and moved the adjustment a single notch and like magic the shifting was perfect. Be prepared, small adjustments in the TV cable can make significant changes so don't go overboard as it can destroy the transmission very quickly if you're setting is way off.

- I had planned on using Shiftworks OD shift kit #SC2262 in my console. It looks and functions terrific. Very professional and it looks like it came that way from the factory. Very smooth yet positive detents. The shift setting decal looks factory but with the extra OD marking.

- I had not planned on installing Shiftworks Neutral Safety/Backup Light Switch kit #SW653. I needed to add it to the project. I highly recommend this kit as without it the car will not light up the rear back up lights in reverse. Also without this kit the car can accidentally be started in gear. Generally resulting in bad things happening. This kit is more involved and requires removing some rivets on the factory shifter and running a 4 wire harness under the carpet to the dash. But its definitely worth it in my opinion.

- Be prepared. This is not a cheap project. By the time you're done, it'll cost you $5-6000 parts and labor for the rear upgrade and trans swap, and that assumes you don't run into other issues. 

*CONCLUSION:*
Don't even hesitate. Do It. You won't be disappointed and you'll drive and enjoy your GTO even more if its not sitting in the garage.


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## geeteeohguy (Feb 2, 2008)

Great write-up, Heatwave. Factual, real-world information. Sounds like you greatly improved your car, and yes, you will be getting a lot more mpg at much higher road speeds. Very happy that it turned out well!


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## John Schutt (Aug 27, 2018)

Still a great write up


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