I have a 97 z28, not slp. I am trying to figure out the specs on my rear end. I want to put 3.73 in it but i dont know what it has now. I need to know what information i need to make the change and where i can find it.

 

A4 or M6. That would make it easier to figure out.

If you have an M6, then you have 3.42's (code GU6 on the driver's door jamb sticker). These are "3-series" gears, so you'd order 3-series 3.73's.

If you have an A4, you have either 2.73's (code GU2) or 3.23's (code GU5). 3.23's are also 3-series gears. However, 2.73's are on a 2-series carrier, so you'd have to order 3.73's for a 2-series carrier.

When you're ordering them, it's a GM 7-5/8" 10-bolt.

 

First thing is check your RPO codes:

GU2 2.73 (A4)
GU5 3.23 (A4)
GU6 3.42 (M6)

If you think there's a possibility they may have already been changed or want to double-check use the calculator at www.f-body.org/gears/ When changing gears if you have TCS or not might make a difference too.

Edit: Capn your faster than I am.