I have a 71 Cutlass Supreme convertible that originally had a 350ci with a Muncie 4 speed that has been in the family almost 40yrs. A couple yrs ago I swapped out the 350 for a 455 and now want to change the rear gears and go posi. It is a 10 bolt cover but I cannot tell if it's a BOP or GM and doubt seriously the rear housing etc has been changed. I have spoken to Eaton, Summit & Jegs and am now more confussed. Before I buy a posi and new gears I would like to know definitely.
Thanks, Ted

 

You have the Oldsmobile version of the "corporate" 8.5 inch ten bolt axle, which was used in every 1971-72 Olds A-body that left the factory. The center section (gears, differential, bearings) are the same as those on every Chevy 8.5 inch ten bolt axle. The biggest difference is that the Olds version uses bolt-in axle shafts instead of the Chevy C-clips. This has no effect on the use of the Chevy posi units or gears in this housing.

 

Thanks for the quick reply Joe. I have attached a page from Eaton on passenger car differentials and highlighted the two possibilities, which is the correct one for my car?
19674-010 or 19603-010

Thanks, Ted

 

Neither one. One more time, this is an 8.5 inch ten bolt axle, not the 8.2. Ignore the "c-clip" reference.

As I said above:

 

Wouldn't the "horn" protrusion identify this as an 8.2" axle? The squared one is the Olds corporate under my '71 Cutlass. The car is 52 years old, they've "only" had it for the last 40 so there's a period of 12 years where parts might have been swapped.

Best person to talk to is Monzaz on this board.

 

The one-sided "V-notch" feature in the cover is correct for the 1971-72 corporate 8.5. There is no doubt in my mind, but if it makes one sleep better at night, pull the cover and actually look at the parts inside. Here are more photos of the ears on a corporate 8.5" ten bolt under various 1971-72 Cutlii.

 

If you feel the top of the casting you will feel and or see the brake line has a BOSS tapped and drilled for the brake like brass hose end fitting. that is 8.5 only.
8.2 CHEVY AND 8.2 bop HAVE BRACKETS THAT BOLT TO THE COVER BOLT TO HOLD THIS LINE to the rear.
That should help you. Jim
JD RAce

 

My original 8.5” 10 bolt has a block “O” and parallel ribs on the side. Much better ID features than the cover and horns / no horns.

 

However you will note that yours also has the same "horn" features as on the OP's axle.

 

Since we all like pictures here's an 8.2" with the brake line bracket monzaz mentioned. The OP does not have this so that's one more bit of information confirming he has the 8.5"

 

Joe, I never even noticed that as I have never used the horns / no horns as an identifier. Had this rearend since 1990 and never even noticed those horns.