Hello all, thx. in advance for any help id rear ends. I know there are 9 and 10 bolt rear ends and different vendors that made rear ends for 3rd gen. I know in late 89 GM changed the rear ends to a 28 spline from a 26 spline. What was the purpose of the change to a 28 spline? How do you know the difference between a Borg&Warner, Australian and other 3rd gen rear ends with the rear end still in the car? Did PBR disk rear ends only come with aluminum calipers? I ran across a 88 GTA with a disc rear end with steel calipers and the diff. cover is formed different than normal covers. It wraps around the gear and has a large port, rubber washer or grommet on the cover. I think its a 9 bolt Borg&Warner posi disc rear end and hard to find and very desirable. Any help and pictures would be great! Thx.

 

Smooth cover with 10 bolts holding it on = a common 10 bolt diff. Could be 7.5", could be 7.625". Could have 26 or 28 spline axles. Could have just about any gear ratio.

Cover held on with 9 bolts and has a rubber plug in it is the BW 9 bolt. There's also a BW cast into the bottom of the diff. Although stronger than the 10 bolt, parts are just about non existent.

Smooth cover held on with 10 bolts but has a metal plug in it is the very rare Dana 44. 8.5" ring gear. It was available in the SLP Firehawk and could be purchased years ago from the GMPPC. For the price of one now, it's cheaper to buy a 12 bolt or a 9".

Externally, these 3 diffs are all the same. They all have the same mounting locations to be installed into a third gen. Internally, they're as different as comparing a 12 bolt to a 9".

28 spline axles have a larger diameter than 26 spline axles. That makes them stronger. Because of the physical size limitations of the tiny 10 bolt diff, that's the largest axle that can be installed.

PBR disk brakes are the aluminum calipers. If it doesn't have aluminum calipers, it's not PBR brakes. They became available in 89.