GM 8.75" 10/12 Bolt

Thought i should write something about this odd ball rear end. The GM 8.75" 12 bolt has an 8.75" ring gear mated to the carrier with 12 bolts. Its also called a 10 bolt because the cover has 10 bolts, but this is actually a 12 bolt. I would call it a hybrid, its like the child of a GM 8.5 10 bolt and a GM 8.875 12 bolt. It was used in the mid to late 70's B-Bodies, usually the wagons, or ones equipped with HD options such as towing. This rear end is very strong, but yet it has no aftermarket because it was only produced for a couple of years. Ive only seen two in my whole life, both had 2.41 ratios, and one had posi and the other did not. It came with a 28 or 31 spline axle, and has a 30 spline pinion and 1-1/4" pinion nut, the same specs that the 8.5's have.
The cover looks like this:

Heres one out of a 79 impala sedan

Im almost 100% sure this is what my 78 Bel Air has and its a 2.73 ratio.

I have never seen one either that I knew of . I did read about it though diff list for GMs and GM did make quite

few oddball rears like the Aussie Borg Warner 9 bolt . Some pretty strong but this one like the Aussie is a victim

little to no aftermarket like the 8.2 rears of old. Did you own one of those or seen it in someone else's car?

A long time ago I almost bought one of those from Garys U-Pull it in Binghampton NY for $75.  It was in an Impala I got some parts out of.  
I was like WooHoo a 10 bolt posi rear for $75!!!  (10 bolt, LOL   )  I was THIS close to buying it until I found out it had 2-something gears.  
Seeing as I'd never heard of a GM posi rear with anything higher than a 3 gear, I figured it had an open diff and someone welded the spider gears to make it a posi so I passed on it.  I've never seen another one until today.

Now I'm wishing I got it anyway just to be different.  I'd have one cool-assed 12 bolt rear end!
The way I see it is, if I can buy a HP cam for my Caddy 500, I'm sure somebody, somewhere makes parts for them.


*edit: Yeah, post #427 (giggles) Tri-Power!

I have one of these in my 79 Caprice.  And just this last weekend I saw another at a car show out of a 78 Impala.

According to the owner he had a 3.73 gears installed along with a posi. case.  

Its a B.O.P. 8.2 only.   Not the Chevrolet 8.2.  

I can go on Ebay and get anywhere from 3.08 to 4.11 gears and posi. cases.

The splines on the axles are 28.

For those who want and can't find.  Try Ebay in differentials and search for 8.2 BOP.

The fellow who showed me his car w/8.2, said he had 7000 miles on it and about 100 runs at the dragstrip.

He has a 406 small block w/700R4.

What do you think those Pontiac GTO, Olds 442 and Buick GS ran. Some had 12 bolts. Others had 10 bolts(8.2).

Its funny what diffent parts people are used to, the 8.75, and earlier 8.875 axles are what have been under a lot of my cars, but they were 78 B-body Wagons, 76 A-body Wagon, and the 8.875' are in my 73 Lemans Wagon, and my 71 Catalina Sedan.

Just an FYI. I received a new axle for my 8.75" 12 bolt today from Dutchman Axles in Idaho. $170 for the axle, bearing and seal + shipping. Their listing for 1977 Impala wagon showed a 31 spline but mine is a 28. They custom built it based on the measurements from my damaged axle. Their listing for a 1975 Caprice convertible was really close to my Impala except for the button width. It looks like a very nice part and the rep was a nice guy.