So everywhere i checked told me my 71 Cutlass S had a 8.5 corporate in it. So I went ahead and ordered a new differential, gears, and rebuild kit blindly. Now that I climbed under the car, the differential cover has the scallop'ed cover on it that I see comes on the BOP 8.2

Can anyone tell me for certain here are some (shitty) pics.

20140428_194948_zpsvbjmn0oh.jpg

20140428_195000_zpsvjioytud.jpg

20140428_195009_zpsp7trkhk9.jpg

 

I think all '71 Cutlass came with the 8.5" 10 bolt rear, but you can easily verify what you have. Look on the side of the center section. Two parallel ribs = 8.5" and 1 rib or 2 converging ribs = 8.2".


Here's a pic from another thread:
https://classicoldsmobile.com/forums...p-10-bolt.html
DSCN3345.jpg

 

Looks like a 8.2 with the moon shaped cut out diff cover.

 

I guess I'll climb further underneath it tomorrow and check. Thanks guys.

 

If I'm not mistaken, complete A-body rear ends will swap pretty easily from 64 to 72.
Your car was probably a "victim" of a swap after a rear end failure.

 

That is an 8.5" 10-bolt rear. That is the A-casting. They came with that cover,which looks like the BOP 8.2",but is differnt.The bolt spacing is different.the BOP 8.2" also has a notch in the top of the cover,for a separate bracket for the brake line "T". The 8.5" has a boss cast into the top of the pumpkin itself.The A-casting 8.5" 10-bolt rears came in all of the 71-72 Skylark GS,and the 71-72 Cutlass/442's that were not built in Lansing.If you have the original drums,and look closely along the outer edge,you will see Buick trishields cast into them.

 

Never judge a book or a differential buy it's' cover.

The two large ears on the bottom of the housing clearly discern this as an original 8.5" diff.

 

I concur


The corporate also has axels bolted in not clips

 

Most shops don't know the difference. When I purchased the rear end that came out of a 71 (per jim's/monzaz instructions), I had 2 shops tell me that it was a 8.2". Jim reassured me that it was 8.5" and told me to find a different shop. Third place I went to, the guy seen it and right away knew it was a Buick/Olds rear end with bolt in axles. Needless to say that he did the rebuild, with parts i bought from Jim.

 

Brian,

Can you confirm that the 8.5" has two parallel ribs and the 8.2" does not?
I have been looking for confirmation online and haven't found anything definitive. This would be a much simpler ID than looking at the cover.

 

Open it up and measure the ring gear
Inspect for wear
Count teeth

 

You have and 8.5" 10-bolt,with the large "A" on the top. The BOP 8.2's did not have parallel ribs. The Pontiac has converging ribs and the Buick has a single rib.

 

Yep. Got under it and verified it has the two parallel ribs. Phew. Thanks guys.