Do the '87 cars actually have a 7.5" rear end?

[TommyV8]

Or did the previous owner of my particular one maybe do a downgrade to make a few bucks before he sold it? Today I was looking at an old book about TBs, and on the list of Buick rear end codes it didn't give a code for an 8.50 rear in 1987, only 7.50 and 7.625. The 8.50 was listed for every year before that though. My rear apparently no longer has the sticker with the codes, but on a G-body forum I read that you can measure the distance between the bottom bolt on the cover and the bolt either to the left or the right of it. On a 7.5 rear the distance will be 3.25", and on an 8.5 rear the distance will be 3.75". Sure enough, I measured mine and it was 3.25". The corners look like the pics I've seen of 8.5 rears, however. Anybody have any idea if the 3.25" vs 3.75" thing is B.S.? Or could I actually have a 7.5 rear?

 

[TommyV8]

Here's a crappy pic. The corners are dark and hard to see.

 

[charlief1]

An 8.5 rear cover is round and a 7.5 is kinda oval.

 

[626gn]

Or did the previous owner of my particular one maybe do a downgrade to make a few bucks before he sold it? Today I was looking at an old book about TBs, and on the list of Buick rear end codes it didn't give a code for an 8.50 rear in 1987, only 7.50 and 7.625. The 8.50 was listed for every year before that though. My rear apparently no longer has the sticker with the codes, but on a G-body forum I read that you can measure the distance between the bottom bolt on the cover and the bolt either to the left or the right of it. On a 7.5 rear the distance will be 3.25", and on an 8.5 rear the distance will be 3.75". Sure enough, I measured mine and it was 3.25". The corners look like the pics I've seen of 8.5 rears, however. Anybody have any idea if the 3.25" vs 3.75" thing is B.S.? Or could I actually have a 7.5 rear?

I could be wrong but my understanding is all TR's came with a 8.5" ring gear but not all of them were posi. It is a fact that the heavy duty 8.5 that came with these cars were very popular and many got stolen.

Check the the front of the pass side axle tube. There should be a stamped code with letters and numbers about 1/4" in height. You might have to clean the area to find it. If it has a 3TP it's a 8.5 limited slip posi. If it has a 3TJ its a 8.5 peg leg. These codes only apply to an 87 TR. If it has any other code then it is not the rear end that originally came with the car.

There were 7.5 and 7.625 ring gears that went into other cars but not a 87 TR. At least that is my understanding...

 

[626gn]

Check the tag in the trunk also. G87 = 8.5 ring gear. G80 = posi. GU6 = 3.42 ratio

 

[QwikStop]

Here's a crappy pic. The corners are dark and hard to see.

That's an 8.5..

 

[TommyV8]

After doing a search for 7.5 vs 8.5 pics, mine really does look more like an 8.5 (rounder cover, triangular bottom corners). The RPO sticker does list GU6, G80, and G87, so my car did come with an 8.5 with 3.42s and a posi. I think that book and that post on Gbody.com must be wrong and that my suspicions were unfounded. Thanks guys!

 

[psycho6cyl]

Wasnt another way to tell 8.5 was if it had that raised middle?

 

[TommyV8]

Someone else did say that somewhere, and mine is raised in the middle. I guess I didn't really do enough research before I made the post. Oops.

 

[TexasT]

http://www.buickperformanceclub.com/85rear.htm

Pix for you to peruse.

 

[novaderrik]

Wasnt another way to tell 8.5 was if it had that raised middle?

and the center section of an 8.5 is just bigger and bulkier in every way than a 7.5- going off that pic, this thread is about an 8.5..
every turbocharged Buick Regal built between 84 and 87 came with an 8.5 with 3.42 gears from the factory.. period. end of story. the only other factory installed application for the 8.5 in a G body was the Olds 442 with the mighty 307, but those had 3.73 gears. every other G body had a 7.5 with 26 spline axles, with the later 87 and 88 Monte SS's getting the upgrade to the 7.625 ring gear and 28 spline axles..

 

[BobbyBuick]

The Mote SS had a 7.5 Cutlass and Regal had 8.5 my 87 Monte had an 8.5 .
One time I bought a Roller checked codes in the trunk and got it home.Owner swapped to to a 7.5 Sucked

If you 8.5 looks like this it is broken

 

[novaderrik]

one other thing that could theoretically happen: someone could put an 8.2 out of a 64-72 A body in one of these cars with the proper conversion control arms that a few places used to sell for putting 12 bolts into them... they use a cover that's interchangeable with an 8.5, and a few people have been fooled by them in the past... they have a smaller pinion nut than an 8.5 and the housing itself isn't as beefy, but they don't have the triangular pads cast onto the bottom of the housing..