[john67455]

Hello All, I'm having a bit of a disagreement with a major parts vendor and am hoping somebody can help me out. I bought a new posi-traction differential and gear set for my 1967 GP without doing any real research except for relying on what the website said. I was assured the parts would fit the car, but unfortunately they don't. I basically purchased an 8.2" rear end set-up. Obviously wrong to most of you all, but not to me until I tried to put it in. Everything went well until I removed the diff cover and the differences became obvious.


The problem is that I had already installed the ring gear and side bearings on the new carrier and the parts supplier won't take them back. So, I'm out $1,300.


To help solve this, some real documentation describing the rear ends that came in the '67 Grand Prix would really help. I'd like to be able to show the parts supplier that no '67 GP (or other full size Pontiac for that matter) was delivered with an 8.2" rear end. If I can prove this, I have a better shot at getting them to take it all back since they clearly state that an 8.2" should fit my car.

I have the '67 service manual and while there are separate sections for the full size and mid size bodies, the details of rear end sizes are not spelled out.

Thanks for the help.

[Ben M.]

1967-1968 Pontiac big car rear ends are an 8.875" or 8 7/8" axle. They are a 12 bolt ring gear with 10 bolt rear cover (10 bolt rear with 12 bolt innards). The 12 bolt ring gear is NOT the same as the Chevy one despite being the same diameter. The axle retainers bolt in (non C-clip).

The 8.2 rear end is for an A-body and a '69+ G-body. Like most manufacturers, they are assuming the post 1969 stretched A chassis Grand Prix is the same thing as the 1968 and earlier B chassis Grand Prix and they are definitely not.

[john67455]

Thanks for the reply. I learned all that, unfortunately after the purchase of the 8.2". My problem is that there doesn't seem to be any articles, publications, etc, that give any real detail about the 8.875" Pontiac rear end and which cars got them. It seems that it's clear that they came with the 8.875" rear but documenting this is tough. Hopefully somebody has something....

[Ben M.]

Are you asking for engineering drawings or part numbers from books? A technical service bulletin? Because if the factory service manual information isn't enough to convince these people, I doubt anything will. I also doubt you'll find some service procedure or bulletin stating the specifications of the rear end beyond what the service manual has already done. The dealers and service people only needed part numbers and interchange books and all of those refer to the rear end by body style and the axle ratio only.

The matter is, they have their facts mixed up and have lumped in the A & B body Grand Prixs together because they likely have no clue (Ames has also done this too). That is on them, not you, to correct. You should not be required to put together a documentation package stating what cars from 1967 came from the factory with. If they require documentation, they need to state what they will accept. I suspect even if you did put together engineering drawings and a fine presentation with signed statements from '60s & '70s Pontiac engineers they would just ignore you.

[john67455]

Thanks for taking the time to help. You make a good point and I will push on with what I have.

How does this sound for an argument:

The service manual definitely differentiates between full size and mid size body styles. Therefore there must be a difference and the rear ends aren't inter-changeable. If they were inter-changeable why have separate sections in the manual. And finally, why have different service tools to work on each rear end. The logical conclusion is that they must not be the same.

How's that sound?

[north]

Almost all major online parts vendors and most auto parts parts listing systems have major application problems with our era of cars. For example if you go on summit or rockauto they will recommend A body brake shoes for fullsize cars.

[Ben M.]

Originally Posted by north

For example if you go on summit or rockauto they will recommend A body brake shoes for fullsize cars.

This has really gotten bad in the last 3-4 years with the latest revisions to the computer interchange software most parts place reference. Suspension parts, brake shoes, rotors, etc are all listed as being the same for a B-body as well as an A-body in many years. In some cases the wagons are the only ones that have this mistake, others it's only Catalinas and not Bonnevilles, sometimes its 1968 only cars vs. 1972 cars, etc. You really need to know what you're ordering before you do otherwise you're dealing with a LOT of mistakes that need to be returned and corrected.