jo75olds

Well I am working on my '75 Cutlass Supreme 442 Tribute

I got the RAM Air Hood, the 455, the TH400, it's ready to roll, but I was just about to order my posi and rear gears when it hit me!

"I NEED A 12 BOLT"

Soo some searching I did, and we all know that GM stopped the 12 Bolts in 72 (I believe it was 72)

So I found some that were pulled from an A-Body that will fit a "64-72" A-Body, but what about my 75???

Would love all the help you guys can give,

Thanks a lot,

Jim

2blu442

Jim, read through the differential section. Both Monzaz and 507OLDS do rear end work and have a lot of knowledge on this topic. I believe you have the 8.5 corporate 10 bolt right now. That's a very strong rear end assembly and easy to find parts for... like a posi carrier and gear selection. I think you'll want to keep what you have and just install the componets you want. But I know there's lots of posts on this topic. Please read through and create a post on anything you have questions on. Either Jim or Brian can supply you with whatever you need to upgrade your rear end. John

jo75olds

Cool, thanks a lot, I was acctully just reading through there, but I didn't really see anything about the '75s so hopefully one of those guys post on here

J-(Chicago)

75 should have a 10 bolt 8.5" with bolt in axles.
Any 68-72 12 bolt rear end would be incorrect.

monzaz

THERE WAS a 73-77 A-body rear that had 12 bolt ring gear bolts BUT the inspection cover was 10 bolt (and resembled a 10 bolt 8.2 rear cover but larger in diameter.)

This rear was installed in the el camino and olds and Monte carlo option performance rear. It came with 11" brakes also. 5 on 4 3/4 bolt pattern.

You can also use the 1978-1985 CAdillac, and other B-body car rears that came with this SAME rear, it will fit directly inder your 73-77 A-body car.

You will need to swap out the axles with any 10 bolt 8.5 axle as long as you have the 28 spline version which in 78-85 were all 28 spline.

IF you find an original one from the early seventies it will be 31 spline.

NOW the big head ache... NOT gear support for this 12 bolt rear- 3.42 was probably the best ratio out there for this rear that is actually FINDABLE.

SO in my opinion USE your 10 bolt 8.5 rear IT IS VERY STRONG and can be upgraded to 30 spline for 12 bolt strength if needed.

JUST pm me and call I will explain the whole thing if you like.

JIm
J D Race.com
330 659 7117

jo75olds

Ok thanks alot, you guys have been real helpful here, looks like I be keepin' my 10 bolt