Local guy is parting out a 70-72 Pontiac Grand Prix and a 70-72 Pontiac Lemans/GTO (thats the way the ad reads). I'm wondering if the rear end of either would be an exact swap for my 70 Malibu if I can possibly get a 12 bolt posi out of the deal to replace my original 10 bolt.

Thanks - Jim Poks

Pontiacs never came with the 12 bolt. Olds did make one, but on the inside, it was a 10 bolt. The upside to the BOP 10 bolts is they came with bolt-in axles, so no c-clips to break. They also have a slightly stronger 27 spline pinion gear, vs. the Chevy 25 spline.

the rear end will fit and i do believe pontiacs did have some 12 bolts in them.i know the gto did.. if it has 12 bolt cover and 12 bolts on the ring gear its a chevy type 12 bolt .the pontiac may have the bigger pinion yoke on it so you might have to use a basterd u jount on it

Our 400 4 speed '72 Lemans Sport was built in Oshawa. It came with a Chevy 12 bolt 3.55 rearend. I had the rearend apart while restoring the car and it is definitely Chevy. Might be an Oshawa thing?

Hmm, never heard of them being stock. Definitely didn't happen in the 60's, must've started in the 70's. The '71 GTO I have out front is a 10 bolt.

Pontiac did use 12-bolts on Lemans & GTOs, plus Grand Prix, but only when the car had a 455 from '70 - '72; otherwise it was the corporate 8.5" 10-bolt. You could find a 12-bolt 3.31 (3.07 on GP, plus on Lemans / GTO with a/c) behind an L75 455 or a 12-bolt 3.55 behind a LS1 455 H.O. The '70 - '72 10-bolts could be 2.56, 2.73, 2.78, 3.08, 3.23, 3.55 plus the rare 3.90 (last used on '71 400) & 4.33 (not after '70 Ram Air).

Even if it is a Pontiac 10 bolt, it will be a little stronger than the Chevy 8.2 10 bolt that you have now. It should bolt right in.

thanks all - very interesting information. The Grand Prix is a 400 and the Lemans/GTO is a 455. I'm going to check them out. He also has the engines for sale.

Jim

well - both are 10 bolts. the gto has a 10 bolt open end and the grand prix has a 308 10 bolt posi on demand. the 400 engine still runs but with rod knock. the 455 is gone. passed on both and will wait for another opportunity for a 12 bolt. thanks all

jim

Were all BOP rears 8.5's? Are parts expensive for those, or the same as a chevy rear?

The BOP 10 bolt is an 8.2. The "O" axle is an 8.5, and the corporate 10 bolt is an 8.5. Parts for the BOP and O are more expensive than Chevy parts. The cororate 8.5 has the cheapest parts.

The corporate 10 bolt is what is found on SOME chevelles, correct?

Few Chevelles got the corporate 8.5 10 bolt.