I purchased an 82 Z28 from a kid that did some "upgrading". According to him, it has a posi with 3.73 gears that came out of a trans-am. I checked for tags on the diff but there are none...so all I have to go on is what he told me. He said it was "some metric something...there is a smaller metric and a bigger metric one, and its the bigger one" To my issue...what were metric differentials? Are they any good? What are other alternatives? Thanks for any help in advance.

 

Don't know anything about metric stuff. The 7.5 rear end isn't metric. The early 7.5 had a smaller pinion bearing that was upgraded to a larger bearing sometime around '82.

 

So when you took the cover off and LOOKED, BEFORE you bought it, what did you ACTUALLY see?

What you saw is what you got.

 

Never trust what some one says when they're trying to get your money. Like posted above, you will need to take the cover off and look at the ring gear and carrier. The gear ratio should be stamped on the ring gear. How many bolts on the rear end cover? 9 or 10

 

So does anyone have any info on metric rear ends offered in Trans Ams? Or other alternatives for a better platform for upgrading? 10 bolt vs 12 bolt vs 9"? I am new to the GM scene so any help is appreciated. Thanks.

 

Don't know where you are getting this metric stuff from. The only thing metric on the GM 7.5 10 bolt is the wheel studs.

The 7.5 can hold up to some street abuse if you upgrade a few things. The '82 to '89 had 26 spline axles. You can upgrade them to the '90 to '92 28 spline axles if you also upgrade the differential to one with 28 splines. The Auburn differential that was used in them was junk. The Eaton Posi or Eaton Truetrac are both nice upgrades. The ring gear diameter was upgraded from 7 1/2 inches to 7 5/8 inches around '86 and as far as I know all after market gears are the larger 7 5/8.

 

Forget the metric handle for a minute. How many bolts in the cover? That'll give us a clue as to what you have and what you might be able to do to it.

 

If the rear is a 10-bolt, the following FAQ may prove useful:

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

JamesC

 

The metric stuff is simply what I was told. I did find that thread JamesC, thank you very much. When I get a chance I will count the bolts. Any more insight and info is appreciated.

 

there are 10 bolts on the rear cover...trying to upload a picture but phone/computer are arguing....

 

10 bolts means you have the 7.5 rear end. The '82 will have 26 spline axles.