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Discussion Starter #1
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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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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: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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Discussion Starter #4
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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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 :D
 

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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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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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Discussion Starter #8
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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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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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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Discussion Starter #11
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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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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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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Discussion Starter #14
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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Discussion Starter #16 (Edited)
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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Discussion Starter #18 (Edited)
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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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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