# I found a GTO Posi rear end for sale $2,500 (what are your throughts?)



## 66CHEEVO (Jan 24, 2021)

Hi everyone, I stumbled accross a GTO Posi rear end for sale. The seller is asking $2,500 which sound a little high and hoping I can get your thouhts.
I know the obvious way to go is with a 12-Bolt Chevy; however, the ones I've come accross are too pricey or in bad shape.

Here are the details and link.

Pontiac posi rear end w/ 3.55 gears. Fits 1964-1972 GM "A" body cars direct fit. New American bearings & seals, new Dorman ring set. Pontiac's heavy duty posi unit (carrier). This carrier in Nodular iron not cast iron & has 4 spider gears not 2. This posi came factory on all Ram Air & HO GTOs & Firebirds. The housing is 1967 date code, very clean & smooth, painted Rustoleum black, New wheel cylinders, brakes & spring kit w drums. Ready to install.









Pontiac GTO posi rear - auto parts - by owner - vehicle automotive...


Pontiac posi rear end w/ 3.55 gears. Fits 1964-1972 GM "A" body cars direct fit. New American bearings & seals, new Dorman ring set. Pontiac's heavy duty posi unit (carrier). This carrier in...



sandiego.craigslist.org





This would be going into my 1966 GTO which currently has and oldsmobile 12 bolt cove / 10 bolt carrier on my vehicle.

It sounds like the seller is willing to take $2,000.

At the moment my only other alternative is a 1968 GTO, LeMans, Grand Prix 3.55 Posi diff assy (ZH 291 N #9798896). He noted it looks good but has a chipped tooth on the ring gear and is asking $950. Here are some images of the 3.55 posi with the chipped tooth. 

I was thinking on rolling the dice on the 3.55 Posi with chipped tooh for $950 as nothing up was comming up in my area; however, I just stumbled accross the one above on craigslist. 

Any feedback is greatly appreciated.

Thanks


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## Baaad65 (Aug 29, 2019)

2K doesn't sound bad but is there shipping costs? 3:55 not going to wind the motor to much is it ? Any warranty, did you check out the seller ??


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## 66CHEEVO (Jan 24, 2021)

Baaad65 said:


> 2K doesn't sound bad but is there shipping costs? 3:55 not going to wind the motor to much is it ? Any warranty, did you check out the seller ??


Hi Baaad65, I'm still waiting for the seller to get back to me. Unfortunately I dont know if this guy has a shop, rebuilt in his garage or accuired from someone else. I'm hoping he has pictures of the build and or receipts. Not sure if the 3:55 gears are going to wind the motor much; however, I'm sure it will do a heck of a lot better than my current 2:56 gears. This will be my daily driver and plan on doing A LOT of highway driving so 4:11 gears where out of the question.

Thanks


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## O52 (Jan 27, 2019)

3:55s will put you around 3000 RPM at 65-70 depending on your tire size. Some people don't like the noise, thinking the engine is going to blow up lol. 3000 RPM is right near the engines sweet spot


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## Lemans guy (Oct 14, 2014)

12 Bolt Built to Order Housing & Axle Package - Moser Engineering


12 Bolt Built to Order Housing & Axle Package 12 Bolt Built to Order Housing & Axle Packages.All Moser 12 Bolt Housings are designed and manufactured in the U.S.A. using Moser Engineering owned Casting Boxes.Package includes; New Moser 12-Bolt Made in the U.S.A. Housing, with OEM located...




www.moserengineering.com





this will cost more, but you should check prices with them and see where it lies…then you pick a 3:42 or a 3:36 as well.


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## Duff (Jan 12, 2020)

Lemans guy said:


> 12 Bolt Built to Order Housing & Axle Package - Moser Engineering
> 
> 
> 12 Bolt Built to Order Housing & Axle Package 12 Bolt Built to Order Housing & Axle Packages.All Moser 12 Bolt Housings are designed and manufactured in the U.S.A. using Moser Engineering owned Casting Boxes.Package includes; New Moser 12-Bolt Made in the U.S.A. Housing, with OEM located...
> ...


If you end up going new, then a 9" FORD is great choice.


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## LATECH (Jul 18, 2018)

Meh. It looks tired. What if it has bearing noise,or ring and pinion noise? You can build one with all new yukon parts for less
I say pass, go to randys worldwide. Get some yukon and get busy


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## LATECH (Jul 18, 2018)

I also have a complete rear ,in good shape for a 64-66. It has a 3.23 open, but it is a solid housing with new brakes for a build.
If you already have a rear, you should take the plunge and build one.You will be money and smiles ahead


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## Baaad65 (Aug 29, 2019)

Piratebates said:


> Hi Baaad65, I'm still waiting for the seller to get back to me. Unfortunately I dont know if this guy has a shop, rebuilt in his garage or accuired from someone else. I'm hoping he has pictures of the build and or receipts. Not sure if the 3:55 gears are going to wind the motor much; however, I'm sure it will do a heck of a lot better than my current 2:56 gears. This will be my daily driver and plan on doing A LOT of highway driving so 4:11 gears where out of the question.
> 
> Thanks


I'm running 28" tall tires 275/60/15 and I'm at about 2400 rpm at 60mph with a 3:42 cog. If you don't plan on running that big of a tire it's going to put your rpms up there so maybe consider a 3:23 or 3:36 especially if you said you want a lot of highway cruising, just a thought.


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## 66CHEEVO (Jan 24, 2021)

Thank you everyone for the feedback 


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## armyadarkness (Dec 7, 2020)

Piratebates said:


> Hi Baaad65, I'm still waiting for the seller to get back to me. Unfortunately I dont know if this guy has a shop, rebuilt in his garage or accuired from someone else. I'm hoping he has pictures of the build and or receipts. Not sure if the 3:55 gears are going to wind the motor much; however, I'm sure it will do a heck of a lot better than my current 2:56 gears. This will be my daily driver and plan on doing A LOT of highway driving so 4:11 gears where out of the question.
> 
> Thanks


If you plan on doing ANY cruising, 355 are the max to go!!!! I have 336's and I tach 3400 rpms when cruising on the highway, going 80 mph.

355 is going to allow you to cruise at 70 MPH on the highway, and have fun on the streets.

AFAIC, $2000 is way too much to pay for a 50 -year old diff, without provenance.

Personally, I'd haggle on the chipped gear diff and throw in new gears for $300, but if you have $2000 and the diff is legit?

However, new black Rustoleum isnt going to compensate for 50-year-old axle, carrier, and pinion bearings and seals... so without proof, you may spend $2000 and have to do all of that, anyway.


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## armyadarkness (Dec 7, 2020)

BTW, cruising at 70 mph with 355s will still have you taching up... so not sure what rpms you want to be at.


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## Drewm (Jul 27, 2021)

An alternative, if you are willing to build it yourself and dont care too much about originality, is to find an 8.5 rear from a 71-72 olds/buick A body. They will bolt in, although you may need to shorten your driveshaft. 8.5 rears are stronger than the 8.2's and you can get a plethora of gear ratios and parts, since these rears ended up being the 'corporate' rear for GM. I am building one right now and when it is all said and done, Ill have about a grand in to it, plus some elbow grease.


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## 66CHEEVO (Jan 24, 2021)

armyadarkness said:


> BTW, cruising at 70 mph with 355s will still have you taching up... so not sure what rpms you want to be at.


Army, to be honest with you I'm not sure what rpms I'd like to be at.the obvious goal is to find a good middle ground which will depend on the intended use. 
I've owned my GTO for a little over a year. When I bought her she came with a low compression '73 400, 600 cfm edelbrock, 4 speed m20 and 2.56 rear gears. I drove her home from Glendale CA to San Diego. It was mostly freeway driving. I drove her home going 75 to 80 mph in the fast lane with my dad following almost the entire way. Between the fact that i just bought a GTO and the 2.56 gears made it the sweetest ride of my life. She pured like a cat. At the time I didn't know what gears I had. I honestly thought I needed a new clutch as when I gassed it from a stop the engine spun a bit. 

Im now in the process of rebuilding the engine and trying to bringher back to her glory. As nice as the 2.56 gears are on the highway they gotta go.

I have an idea on what I'm in for with the 3:55 gears. I currently use my 1977 toyota pickup with a 20R and 4 speed manual transmission. I drive it on the freeway going 70-72 regularly. At that pont its reving pretty hard. When 80 its no longer fun. Sometimes I find myself looking for a 5th gear. 

As many people do, I'll probably end up re-gearing my rear end in a few years to 3:23 or 3:36 gears and see the difference. 

Things are starting to fall into place. I just picked up my block, heads and crank from the machine shop today. Ive been waiting almost 2 months. The gave me plenty time to do my research and aquire parts.

Anyhow, I just wanted to share my story. I'll be posting some pictures on my progress soon?
















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## armyadarkness (Dec 7, 2020)

Obviously, you want a gear that's fun, yet puts as little wear on your engine as possible. Many of these guys in here never leave the local streets or shows with their cars, taching 4000 rpms is okay for them, because the car only runs a few hours a year.

My car runs a few hours a week, on the parkway, so 4000 rpms for 2 hours is a lot of life... but still much less in the grand scheme than a daily driver


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## Baaad65 (Aug 29, 2019)

66CHEEVO said:


> Army, to be honest with you I'm not sure what rpms I'd like to be at.the obvious goal is to find a good middle ground which will depend on the intended use.
> I've owned my GTO for a little over a year. When I bought her she came with a low compression '73 400, 600 cfm edelbrock, 4 speed m20 and 2.56 rear gears. I drove her home from Glendale CA to San Diego. It was mostly freeway driving. I drove her home going 75 to 80 mph in the fast lane with my dad following almost the entire way. Between the fact that i just bought a GTO and the 2.56 gears made it the sweetest ride of my life. She pured like a cat. At the time I didn't know what gears I had. I honestly thought I needed a new clutch as when I gassed it from a stop the engine spun a bit.
> 
> Im now in the process of rebuilding the engine and trying to bringher back to her glory. As nice as the 2.56 gears are on the highway they gotta go.
> ...


Have you considered a five speed then the 3:55 would be ok or a taller first gear in a four speed, I have a custom 4 spd with a 2:98 first gear. Maybe a Gearvendor overdrive?


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## Sick467 (Oct 29, 2019)

This topic is in the back of my head all the time as I will need to make the rear gear decision in a year or two with my build. My 67 has the 2.56 single peel rear. Even though I love the highway mileage and the fact that it will chirp the tires at 55 mph going into 2nd...It's a slug off the line. I have not done enough research yet, but I am leaning towards converting my rear housing to a safety-track and considering the lowest gears it will take (maybe the 3.23 or 3.36). I think I have read the the lowest gears the 2.56 housing will take is the 3.36. Somebody correct me here if I'm off-base.

EDIT: I am confusing the housing with the carrier. Fairly sure the housing will handle all the gear ratios, but the various carriers only handle a few ratios.

My problem is that if I choice to go lower than my housing will take...I have to source a new unit and the Gearvendor Overdrive starts nagging me to spend more money to get some highway comfort back. Very cool, but pricey.


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## Baaad65 (Aug 29, 2019)

Idk what trans you have but you could go with a low geared 1st gear 5 speed or can you get a lower ratio 1st gear in an auto w/overdrive then do the 3:23 or 3:36, you'll get the best of both worlds also your rpms at higher speeds depends on tire height.


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## Sanders Speed (Oct 23, 2020)

Agree with Army. Seems high price. If you have a housing, put new gears and new posi carrier in it. The 4 pinion HD posi will wear out and probably is. Cone style clutches in the carrier are metal to metal resistances. You can turn the base of the cone to get more grip. As for ratio, a lot of ways to go. I have 428cid 5 speed tkx and 3.55 gears. Had 3.55 with 4sp. Tried 4.10s and 3.23s. Went back to 3.55s best of both worlds.


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## Baaad65 (Aug 29, 2019)

I can give you the contact information from the guy I bought my 12 bolt from, think he's in North Carolina? That's all he does, mine was the shorter version for a '65 w/flat spring perches, Strange axles, Eaton posi, new seals, backing plates, painted and a 3:42 gear for 2100.00 I think it included shipping but that was four years ago.


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## Mine'sa66 (Oct 30, 2019)

I bought brand new, custom built Chevy 12 bolt for my '66 from JDRace.com.
Complete, with brakes, $3000 shipped to my door.
Great folks, great product, great service


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## Red Skeleton (Jul 2, 2019)

My 2 cents, my 68 has a 355 ten bolt with a m21 and I also find my self looking for a fifth gear. The engine sounds like it's winding so I keep it at 55-60. Maybe 3K rpm is the sweet spot and I'll have to get used to it? It's VERY quick at slower speeds but I wish I had that 5th gear.


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## z man (Jun 20, 2010)

I had 3.55 gears in my 68 with the th400 trans. Highway cruising was well over 3000rpm. Switched out to 3.08 and still push 3000 rpm at 70mph. You have a set of crushing gears now at 2.—- Just put in a limited slip to accept those gears and cruise. Everyone is out for blood on the highways. No enforcement on speeding . You would be the right lane poppop


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## z man (Jun 20, 2010)

Crusing


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## z man (Jun 20, 2010)

F—. Cruising


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## varmit86 (Nov 7, 2009)

A big question is how original is your car? If it's not do the 9 inch Ford conversion from Currie, bolt right in, super easy to swap center sections with gear ratio. 3:55 is a good all around gear.


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## geeteeohguy (Feb 2, 2008)

$2500 is too much for an 8.2 3.55 posi rear IMO. By about $1000. You'd be better off with an 8.5 corporate rear end in the ratio of your choice. I've owned and driven 3.55 geared GTO's over the years and for open road use, they run too high an rpm for my taste. For a 4 speed GTO a 3.23 is the best 'compromise' ratio and for an automatic car, a 2.93 or 3.08 is about perfect. With a 4 series carrier, you can run 3.36--4.33 gears, ,but not 3.23's. The 3.23 uses the 3 series carrier which works for 2.93-3.08-3.23 gear ratios. If you do a lot of driving, 3.55's get old fast. When I started out, the national speed limit was 55 mph, so 3.55's were fine. These days, with traffic moving 80 mph, you will be stuck in the slow lane winding out and guzzling gas. JMHO......


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## Noangelbuddy (Dec 6, 2017)

My two cents: Moser was already suggested, I would also check out Spohn Performance. You can get a new posi rear with gears of your choice for under $3k, other options like powder coat will drive price higher. Getting a quote for your options doesn’t cost you anything except your time; it can help you make an informed decision.


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