# 1968 GTO rear end question



## mrvandermey (Jun 15, 2011)

Hey guys, I know this subject matter, rear ends, has probably been beat to death. But as we all know, 12 bolt rear ends are getting pricey out there. Anyways, I have a chance to get a 12-bolt rear end housing (without differential, gears and brakes) for a decent price.

My question is there is a difference in Pontiac rear ends versus other GM A-Bodies? I thought I heard that Pontiac, Olds, and Buick have a different rear end than Chevrolet, is that correct?

The "numbers are 40992 cant read very good 255 has R2 had 2.56 gears has C10 measures Flange to flange 55 3/8 long..All mounts look same as 70 Chevelle,, has Carrier Main Caps and bolts.I think these came in 68,69 Skylark,olds 442,Cutlass". Sorry, I am quoting seller here.

Is this a rear end just for Olds and/or Buick or can it be used on a Pontiac?


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## ALKYGTO (Mar 29, 2010)

You *don't* want the Olds 12 bolt. It still has 10 bolts on the ring gear and the "12 bolt" is in reference to the cover only.

Pontiac "10 Bolt" is superior in strength to it anyway. 12 bolt Chevy style is the strongest *GM* rear for these cars and many aftermarket companies offer the Ford 9" which is nice because it is strong, offers mucho gear ratio choices, brake options and superior axle bearings (no c-clips).

For ultimate strength consider the Dana 60 and now I hear Strange Engineering is offering a BIG 10" rear axle that will bolt in GM a body's. 

It all depends on your goals and budget but I would say if you are starting from scratch check out Currie, Strange and others for a 9" Ford rear.


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## BearGFR (Aug 25, 2008)

:agree With what the man said. The terms 10-bolt and 12-bolt refer to the number of bolts holding the ring gear onto the carrier, NOT the number of bolts on the cover. There are some type-O axles out there that have 12 cover bolts, but inside they're really just a weaker version of the 10-bolt.

This is what the "Type-O" ("pretend" 12 bolt cover looks like)









And here's what a 'real' 12 bolt cover looks like









Bear


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## mrvandermey (Jun 15, 2011)

Thank you, thank you gentlemen. This information is exactly what I need to hear. I am going to pass on the Olds rear end. Instead, I am going to use that money to buy a factory endura bumper thatis straight and already prepped to be installed and painted (yes, I realize even with a factory endura bumper, that there will require sanding and fitting to make it fight right).


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## FlambeauHO (Nov 24, 2011)

Remember, depending on what you have planned for your engine there's nothing wrong with a good old Pontiac 10 bolt with an Eaton or Auburn posi unit. Mine is running great so far


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## kilkm68 (May 5, 2011)

Pontiac did use the Chevy 12 bolt rear ends in the 1970 455 GTO's and Grand Prix. I have one under my '68.


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## BearGFR (Aug 25, 2008)

Indeed. Unless you're making more than 500 lb. ft. of torque, and/or plan to make a habit out of dumping the clutch in a manual trans car, the factory 10-bolt in good condition ought to last for a good long while.'

Bear


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## mrvandermey (Jun 15, 2011)

No, I am not planning on anything more than 450 HP and I am not a racer, but am more of a boulevard cruiser. 

How do I know whether I have a Pontiac 10 bolt or just a GM 10-bolt (I know my current rear end is not original to car)? What are the differences between GM, Chevrolet, Buick/Olds and Pontiac rear ends (either 10 bolt or 12 bolt)?

If I get a Chevelle rearend (there is a 12 bolt from a 1969 Chevelle that is for sale locally), and want to or need to change differential, gears or axels, do I need to get Chevy parts or will Pontiac internals work on a Chevy/GM rear end?


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## BearGFR (Aug 25, 2008)

As far as I know, with the exception of the aforementioned "Type-O" axle, all the 10 bolts in GM cars from that era were pretty much the same. Hopefully someone who knows more than me will chime in here.

Bear


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## ALKYGTO (Mar 29, 2010)

mrvandermey said:


> No, I am not planning on anything more than 450 HP and I am not a racer, but am more of a boulevard cruiser.
> 
> How do I know whether I have a Pontiac 10 bolt or just a GM 10-bolt (I know my current rear end is not original to car)? What are the differences between GM, Chevrolet, Buick/Olds and Pontiac rear ends (either 10 bolt or 12 bolt)?
> 
> If I get a Chevelle rearend (there is a 12 bolt from a 1969 Chevelle that is for sale locally), and want to or need to change differential, gears or axels, do I need to get Chevy parts or will Pontiac internals work on a Chevy/GM rear end?


No parts will interchange between the Olds, Pontiac and/or Chevy rears. I have a 12 bolt in my car and put about $1500 into it to make it "right" including Strange Street C-clip eliminators and hardened axles; two must haves in my book because the 12 bolt uses the axle as the inner race for the bearing.


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## mrvandermey (Jun 15, 2011)

ALKYGTO said:


> No parts will interchange between the Olds, Pontiac and/or Chevy rears. I have a 12 bolt in my car and put about $1500 into it to make it "right" including Strange Street C-clip eliminators and hardened axles; two must haves in my book because the 12 bolt uses the axle as the inner race for the bearing.


So if I get a 1969 (or any year) Chevy Chevelle 12 bolt rear end, I should expect to use a Chevy differential, Chevy gears, and Chevy axels, right? Will my Pontiac driveshaft fit on a Chevy yoke? Or will a Pontiac yoke work with Chevy differential?

Will only GM A-body rear ends fit a GTO? What about Camaro, Monte Carlo, or a truck rear end?


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## JustAl (Mar 20, 2010)

All 12 bolts are the same internally, however Camaro rear ends utilized a leaf spring making ther use in an A body a no no. "Chevy" 12 bolts were found in "big block" Chevelles, Monte Carlos, all El Caminos, and 455 GTOs. Truck rear ends are to my knowledge different. The overall width changed in 1968, those rear ends are 1/2 inch wider per side, but mounting pad location is the same. Back-spacing the wheels to accomodate this allows them to be used in the '64-67 chassis depending on tire size. C clip eliminator kits should be avoided for street use their design doesn't allow for side loading as encountered during cornering. Moser makers a good C clip axle stronger than stock and non tapered, probably all that's needed for most power applications. Hope this helps.


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## ALKYGTO (Mar 29, 2010)

JustAl said:


> All 12 bolts are the same internally, however Camaro rear ends utilized a leaf spring making ther use in an A body a no no. "Chevy" 12 bolts were found in "big block" Chevelles, Monte Carlos, all El Caminos, and 455 GTOs. Truck rear ends are to my knowledge different. The overall width changed in 1968, those rear ends are 1/2 inch wider per side, but mounting pad location is the same. Back-spacing the wheels to accomodate this allows them to be used in the '64-67 chassis depending on tire size.* C clip eliminator kits should be avoided for street use their design doesn't allow for side loading as encountered during cornering.* Moser makers a good C clip axle stronger than stock and non tapered, probably all that's needed for most power applications. Hope this helps.


The Strange Street C clip kits have heavy duty tapered bearings and are fine for street use.

They also make bolt in 12 bolt housings for GM A bodys as well as the DANA 60 rear to bolt in our cars.


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## mrvandermey (Jun 15, 2011)

Hey guys, sorry for bringing up an old thread, but I thought it better than starting a new one. I have a GM 12-bolt posi rearend I just got off a 1969 GTO parts car. I can not seen to find any numbers on the axle shaft or anywhere on rearend. How do I determine if it is a Chevy 12-bolt or the Oldsmobile O-type (the "fake" 12 bolt)?


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## BearGFR (Aug 25, 2008)

Google up the two axles. There are external visual differences in the covers and once you see them both side by side, it'll be fairly obvious.

Bear


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## mrvandermey (Jun 15, 2011)

Okay, stupid question time....although I am not in front of the rear end right now to verify, but will be shortly....assuming for a moment that I actually have B/O/P O-Type rear end ("fake" 12-bolt), can the inside differential, gears and axels this rear end be swapped out for a Chevy 12-bolt? Or is the housing itself different?


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## ALKYGTO (Mar 29, 2010)

Everything is completely different.


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## mrvandermey (Jun 15, 2011)

OMG.....after a careful examination, I am now pretty sure my 12-bolt rear end that I took off the parts car is not a Chevy rear end but an Oldsmobile Type O "fake" 12-bolt rear end. It appears the cover is smooth and round and does not have the "V" dimple. Oh well I guess my search for a rear end goes on.


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## FlambeauHO (Nov 24, 2011)

Bummer, I gave up on a cheap 12 bolt and had an Eaton unit installed on my oem rear. Knowing I wasn't after high hp in the future I have been very happy.


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## 68GTO4004Spd (Jun 19, 2008)

Just so you know, this is what the correct rear end looks like for your car.


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## mrvandermey (Jun 15, 2011)

68GTO4004Spd said:


> Just so you know, this is what the correct rear end looks like for your car.


That looks like the current rear end I have on the car now. But was planning on upgrading to a Chevy 12-bolt posi. Instead it appears I have an Oldsmobile Type O rear end! Where the cover itself has 12 boots but is really a 10-bolt. The only good news is does appear to be a posi rear end.


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## FlambeauHO (Nov 24, 2011)

Are you planning more power than the Pontiac 10 bolt can handle?


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## mrvandermey (Jun 15, 2011)

FlambeauHO said:


> Are you planning more power than the Pontiac 10 bolt can handle?


No, not likely. I have a stock 400 (350 HP) going in it and may throw in a Stroker 461 (approximately 450 HP) down the road. I am not a racer as much as I am a boulevard cruiser.


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## FlambeauHO (Nov 24, 2011)

I say throw a posi in the 10 bolt and run it till it gives up. Really depends on the likelihood and time frame of the stroker...


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## mrvandermey (Jun 15, 2011)

FlambeauHO said:


> I say throw a posi in the 10 bolt and run it till it gives up. Really depends on the likelihood and time frame of the stroker...


In all reality, the Stroker is likely to be several years away, if at all. My goal right now is to get my car running so I can drive it and finish the build as I go.


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## Instg8ter (Sep 28, 2010)

don't discount that 2:56 gear in a auto, Pontiac motors make enough torque to turn it and i get over 17 mpg on the freeway with 440 HP (if i keep it under 80). Have a 12 bolt chevy in the barn with a 3:55 and i almost hate to swap it for the light to light performance vs. gas mileage. Like Bear said unless your dropping the clutch on a manual a lot, the 10-bolt will hold up to most anything a street motor can throw at it.


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## mrvandermey (Jun 15, 2011)

So what you guys are saying is dump the Oldsmobile Type-O rear end and just keep the 10-bolt I have on the car? Currently, the 10-bolt on car is a non-posi and has one lug broken off; while the Olds Type-O is at least a posi and has all the lugs.


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## FlambeauHO (Nov 24, 2011)

Lugs are a buck or two at napa or online. Just beat the old one out. Got my posi on amazon or ebay for around 350 and installation was a bit more. Dont recall how much as I was having seals and one axle replaced.


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## ALKYGTO (Mar 29, 2010)

:agree Fix what you have and try and unload the Olds 12 bolt to pay for a portion of it. Way better off with the Poncho 10 bolt.


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