hey guys! I have an 85 Iroc with the 700r4, i know the car has 3.23 gears but what size is the rear end itself? I am shopping for gears for my car. I am either going with a 3.73 or 4.10 and i don't know what size the rearend. and info!

 

If it has 10 bolts holding the cover on, it's the 7.5" / 7.625" one. (same thing)

If it has 9 bolts, it's the 7.75" one.

 

The 10 bolt is a GM corporate diff. The 9 bolt is made by Borg Warner in Australia. Parts between the 2 diffs are not interchangeable.

If you have a 10 bolt, it has a 7.5" ring gear. Around 1986, GM upgraded to 7.625" but everything else is still the same. A fourth gen diff is 7-5/8" but it's still called a 7-1/2". When we refer to these tiny 10 bolts, it's always called a 7.5" even though it may have a 7.625" ring gear in it.

A 700R4 and 4.10 gears are a bad combination. The low first gear is too much for the deep gears. It's fun stoplight to stoplight but that's about it. A better combination is 3.73 gears.

 

You need to read the 10 bolt sticky before you start ordering any parts. There is a lot of information in that sticky that will educate you and keep us from having to answer questions that we have answered many, many times before.
https://www.thirdgen.org/forums/tran...-10-bolts.html

 

thanks guys!