Maverick

I've seen numerous photos of 8.2/8.5 - 10 bolt rear ends and none look like mine.

Can anyone enlighten me to what I have ? I thought it was a 8.2 " so those are the gears I bought. Hope I'm right.

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70cutty

It looks like a 8.5 to me.

Maverick

I have never seen those 2 notches on the bottom of a rear end before . That is why I am confused.

Fun71

Look at the side of the center section. Two parallel ribs = 8.5", one rib or two converging ribs = 8.2".

Maverick

]Will do . Thanks.

oldsmobiledave

It is an 8.5". The 71-72 8.5s come in two versions. One with fangs & one with ears. You have the fangs version.

Maverick

Yup. 2 parallel ribs. 8.5 it is . Anyone interested in a set of 3,73's ? lol

Back to the drawing board.

monzaz

That is NO way to tell 8.2 from 8.5

Please send more pictures of the backing plates and the axle tube meeting the center section casting . picture of the yoke will also seal the deal.

Chevy 10 bolt 8.2 also has 2 parallel rib also. So just to be sure you need to do more work. Jim

IF YOU HAVE THE ORIGINAL REAR UNDER THE CUTLAS 1971 IT WILL BE A 8.5 OLDS REAR. but lets be sure.

JD

Maverick

Will do. Not easy I see . I'm not the original owner, so I have no idea.

Fun71

Thanks for the clarification on that. I tried to find pictures of a Chevy 8.2 but couldn't. I wonder why the 8.2" 10 bolt ID diagrams show the ribs on the B and P axles but not the C?

My original has a block "O" on the forward part of the center section where the axle tubes attach. Any idea if all Olds 8.5" 10 bolts have that? If so, it would be a good identifier.

monzaz

You can not do this one by a simple rear cover ID

Is the rear bolt in axle?
What size is the pinion retaining NUT 1 1/8 or 1 1/4 socket?

Jim

or Show us more pictures of the yoke area and backing plate area looking from under the car outward. Back side of the backing plate. Jim

Maverick

Here's 4 more pics.

Sure be nice to know what it is.

monzaz

it is a corp 10 bolt 8.5 the yoke is the dead give away. NOT the 2 parellel casting as chevy 8.2 will have the same parellel web castings.

pinion nut will be 1 1/4" socket chevy will have a 1 1/8" nut. (M3R joint)
The Yoke is a 8.5 design only 1 1/8" u-joint cup with straps not u-bolts a traditionally all BOP rears used. Chevy rears will always use 1 1/16" cup diameter (1310 or 1330) from the factory and could have straps too BUT will have small tabs to hold the u-joint retention the Corp used the inside c-clip cup retention .


NOW there is a 1310 yoke that was used on 10 bolt 8.5 Novas BUT A-body cars never used them from the factory.

So hope that helps

Jim
JD

VI Cutty

Using the yoke identification, would that be an indication that both of these yokes are off a GM 8.5"?

jzee

Not sure if anyone is still around on this thread, but I have basically the same rear end, it is on an older car(1937 Pontiac) and I am not sure what the ratio is, Axle code is ACC1371, Casting is 1243774 but it looked like the upper picture on the other cite. May have been modified because the shocks are forward of the axle not behind. Was told it could be from a Skylark or a Grand Prix, maybe 68-72? not sure, from some of the sites it looked like a 2.73, but others point to 3.08.

Any help would be greatly appreciated, we are in the middle of replacing the suspension due to metal fatigue, with an after market four link.

Thanks guys

monzaz

Yes those are BOTH the size yokes. The YOKE and the nut together is the best way to tell an 8.5 AND the rear cover etc. YOU have to be sure before jumping into a build, Better to be sure before anything.

monzaz

IF shocks are in front of the axle tube it will be a A-body GM from 73-77 OR a 78-96 B-body and if it is wide rear could be a gm full size from 1971-1976 too. See how simple everything is....lol. Jim

monzaz

YOKES are not the only way to tell a rear differential size.
With those pictures i can tell BOTH use the Mechanics 3R 1 1/8" cup u-joint. It could be a 8.5 or 7.5

nEED TO SEE THE REST OF THE REAR LIKE COVER AND AXLE TUBE THICKNESS TO MAKE A CORRECT CALL.

J D RAce
Jim

jfb

this might be a little off the subject but keep it if it is a 8.5. the 8.5 was just about as strong as a chevy 12 bolt and with a little upgrading from moser etc it can handle excellent amounts of power. serious buick grand nationals used them for serious runs and I have 1 one and have had no issues with moser parts of course in the right areas plus most came with bolt in axles that are much safer the chevys c clip idea definetely a upgrade in durability. I would also again suggest that when rebuilding it that you think it through for parts and do the homework first. good luck the 8.5 is excellent.

droldsmorland

Pull the cover and look at the gasket shape, count the carrier bolts and measure the ring gear ID. Look for stamped numbers on the ring gear. Pull the shafts and count the splines. Probably needs a service anyway. The ratio is stamped into the ring gear. It will be 4 digits. Divide the first two digits into the last two.