I have an '85 Trans Am and I am wondering what rear is in it.
I imagine it's stock but I can not find a forum/site to ID the codes. The newest I could find was for an '81. Does anyone have the codes for the rear gears and where they are located on the rear? Just trying to figure out what's back there since I have a 350 sbc in the car that originally was supposed to hold a 305.

 

It could be the 10 bolt or the BW 9 bolt. First you need to figure out which rear end it is. There is a decal on the bottom of the console lid or on the back of the spare tire cover that has all of the codes on it. The rear end codes start with a G. If it has the limited slip differential (posi) then it will have a G80 code. The gear ratio codes are all listed in the FAQ about 10 bolts sticky. Please read it.

 

Alright, I understand the 10/9 bolt differences. So, underneath the spare tire plastic cover there will be one of those factory sticker diagrams? 10 bolt is a posi? or can a 9 bolt also be a posi? I think I was just on that sticky but didn't thoroughly read it. I'll have to get back to it.

 

Almost ever one of the 9 bolt rear ends has the LSD in it. I have only seen one that didn't. The sticker could be on the back of the spare tire cover or on the bottom of the console lid.

 

I'll give it a look after work and hopefully I have a posi because I really don't feel like changing rears or gears

 

I just was able to pull the cover off the spare tire. There was no labeling on there just sound padding. I'll have to jack the car up and check the bolts next I assume.

 

Look at the cover and see if it has a rubber plug and the cover is shaped kind of like a stop sign. That is the 9 bolt. If there is no rubber plug and the cover is oval shaped then it's a 10 bolt. You should be able to see it with the car on the ground.

 

I've tried yesterday. The tires are flat and dry rotted so I couldn't fit under there. Trust me it would have been a lot easier if I could just squeeze under there to take a peak because I know I can on my '91.

 

If you do end up getting under there here is a pic of my 9 bolt on my 85. Hope it helps.

 

9 bolts on the cover = 9 bolt
10 bolts on the cover = 10 bolt.
Being over 27 years old there is no telling whats in there until you pull the cover.

10 bolt sticky = https://www.thirdgen.org/forums/tran...-10-bolts.html


Specs for stock set up are at the bottom = https://www.thirdgen.org/1985-pontiac-firebird

 

Thanks Ronusmc. Still haven't gotten under there yet. Working on two cars i've been bouncing back and fourth with them. Progress is getting made though.

 

I am late of this reply but just seen this post,
As far as the 9 bolt is concerned? Gm stopped making the 9 bolt rear ends in 1989 models, and went to the 10 bolts, the Borg Warner rear ends made there final year in 89 iroc z cars I know 100%, and them went to the 10 bolts from 1990-1992 on all the Camaros and the z28 cars, the j65 option was made with rear disc brakes, and most of them was for all years in 85 and up,
As far as Pontiac is concerned? I believe they carried the and followed the same suite as to the 9 & 10 bolt switch,
Hope this helps new readers,

After you get the number off the rear end, which is located on the top of the rear end, as it will not have a plate or plaque offered for any 9 or 10 bolt, or will be stamped directly which you will need a can of degreaser or a steel wool brush to a good tooth brush to do away with the Greece and find your numbers listed on the rear end,
After u get the numbers just type it in the search bar, and you will find what gear size you have? What type of pose you have? Ect.....
Good luck with it,

 

Thanks for that info man. After doing a ton of research on if it is stock thrn it nore than likely has 3.23's and is open :/ I'm in the midst of pulling the motor for a rebuuld. Once that's all done i'll be upgrading the chassis and rear.