I've got a 72 cutlass s and I'm going to make an attempt at changing the pinion seal cause it's leaking but I wanna make sure I get one that will properly fit is there anyway to easily identify what gear size the diff is without taking the whole thing apart

 

Unless you have reason to believe it's not the original axle, the 1972 Cutlii only came with the 8.5" 10-bolt "corporate" axle.

 

Would this be the same for a 72 Delta 88?

 

No.

 

Here are two good threads on the full-sized Oldsmobile rear ends. Quite rare to find a posi in the salvage yard these days:

https://classicoldsmobile.com/forums...changes-41149/

https://classicoldsmobile.com/forums...estions-55438/

 

It could be a 10 bolt 8.5...BUT it will not have the same width or shock mount and upper control arm placement.
A body Cutlass
B-body 88 /(I think)...Not a platform know guy when it comes to GM full size.
I think 98 was c-body???

 

Jim, you are correct. The 98s were C bodies, Delta 88s were B bodies and the Cutlii were A bodies. I was wondering if the threads I linked were appropriate for Middian because you mentioned in one of the other threads that only the big block cars got the 12 bolt 'O' type FULL SIZE rear. Hopefully Middian can post some pics of the rear in his Delta 88 if he's considering servicing it.

I guess we hijacked this thread BUT...

 

Yes, rule of thumb. 455 Big rear and do not for get WAgons too.
AGAIN...I am sure there was an exception to this that someone will find...lol.

 

Keep in mind that the 71-76 clamshell wagons used leaf springs and a different width rear axle to clear the retracting tailgate.