Bobby455

Hi All,

I am curious as to how you tell whether I have a 8.2 ring gear or an 8.5 ring gear in my 10 bolt. It's non-posi, 28-spline, not sure if that info helps or not.

Thanks,
Bobby

Fun71

First of all, is it under a car and if so, what year car?
Anything 1973-up would not be an 8.2" 10 bolt.

For earlier rears, it could be either. We had a lengthy discussion about this a couple months back and there was some definitive information posted. Sorry, I don't remember all the details but a search would likely find the thread.

Bobby455

under a 71 cutlass, it's the original rear end.

Qwik71442

71's had the 8.5"

Bobby455

I saw on 442.com (not sure how reliable it is but the guy seems like he knows what he's talking about) it said after '70 it could be either or. The only reason I can't look at it right now is because the car is in storage (damn new england winters), so do I just have to crawl under it to know for sure? Or is it definitely 1971's only had the 8.5 10 bolt?

Qwik71442

All 71's came with the 8.5

Bobby455

Ok, perfect, thank you!

olds 307 and 403

More importantly you have the type C 8.5" rear.

Fun71

Huh? Type C means Chevy, right? As in axle shafts with c-clip retainers? A 71 Cutlass should have a BOP rear with bolt in axle shafts.



My original 71 10 bolt rear has a block O where the axle tubes go into each side of the center section. That's a dead giveaway that it's an 8.5" 10 bolt Olds rear.

Pics from two previous threads about this. Read those threads as there is a lot of good information about identifying the 8.5" 10 bolt rear.

https://classicoldsmobile.com/forums...lass-axle.html

https://classicoldsmobile.com/forums...l#&gid=1&pid=1

monzaz

Well I can tell you I have heard and had customer drive in with 1971 Cutlass' that had 12 bolt 'O' type rear under it and it sure as heck looked to be all factory... They were early 1971 car.... Did not get the plant assembly...

But it could be a possibility as if they were left over from 1970 they might have keep using them and there was a strike in 1970 some time I do not know if it lead into early 1971???

I know in 1970 Chevys were factory installed with Pontiac rears and 12 bolt olds rears El caminos, Monte Carlos etc. Were inundated with the BOP rears FACTORY installed.

Just another wrench to through in your works of IDing.

IT is always best to take a picture and we will all check it over for you and then you will know for sure.

Jim
J D RAce

Bobby455

These pictures are probably going to be useless, but these were the last pics I took of the rear end. I will take more this weekend

Bobby455

So here are some pics I just took, of the cover and each side of the differential from the front. Are these any more helpful? The cover doesnt look like the 8.2 cover

Fun71

I'm fairly certain I see a block "O" on the forward facing part of the center section in this picture. That is your confirmation that it is an Oldsmobile 8.5" 10 bolt rear.

olds 307 and 403

So was it a part way through the 71 year swap over to type C 10 bolt rear ends with bolt in axles? I know all Olds rear ends up to 72 have bolt in axles but call them corporate or Chevy, that is was the rear end that won out, big surprise. I always thought they switched in 71, it would make sense to use up any left over Type O rear ends, just like forged cranks in 68. I know the sources say Canadian cars got the 12 bolt type C rear ends in 68-69. Good to know if I ever buy a 71, it may have the Type O.

Fun71

I think the change was later than that. I had a 1975 Cutlass rear that I got a posi carrier out of and it had bolt in axles.

I think you're confusing this discussion with the O-Type 12 bolt rear. What is in the above pics is an Oldsmobile made corporate 10 bolt - ya know, the O in the BOP lineup. I don't know how long the BOP 8.5" 10 bolts were in production before GM switched to the Chevy style axles.

olds 307 and 403

Corporate=Chevy which is why I don't give a crap whether GM lives or dies today. I realize there some differences and Olds kept bolt in axles obviously into the 70's, never pulled the cover on my 76 Cutlass or checked the brakes. I only knew that they kept them through 72 and maybe thought Olds kept them into the mid 70's. It is almost like putting Rocket valve covers on a sbc and calling it an Olds motor.

Bobby455

So can I put a regular 8.5 10 bolt posi in it or would I need to find one that is specific to Olds' O Type 8.5? Same for axles, would I only be able to use the stock 28 or would I be able to upgrade to 30 or 33 with the posi change?

Fun71

Yes.

The O-Type has a 12 bolt cover on it. What you have is an 8.5" 10 bolt rear that was made by the Oldsmobile division of GM.

You can upgrade the posi and axle shafts.

Bobby455

Awesome, thank you so much for your help everybody!

monzaz

The pictures you attached are all 10 bolt 8.5 Oldsmobile
71 72 - 1976 will have that rear cover with the 12 - 3 o'clock angle + plus bolt in axles 28 spline with oiled bearings + the pinion nut being 1 1/4" socket size + 4 bolts and 2 straps with 1 1/8" cup size on the u-joints + The bumps on the casting where the axles press into the center section...ALL are indications of the 10 bolt 8.5 casting...
If the cover was off the caps would have arrows pointing outward at the wheels direction away from the center. then there is the casting number end all be all....
Physical traits are the only way to be sure. NEVER assume you have an original 50 year old muscle car. Most Muscles DO NOT have their original parts in place these days.

Jim
J D RAce