The car in my sig has a factory rearend out of an 86 IROC, with disc brakes, posi, and opposed caliper mounting (1 caliper facing front, 1 facing rear). My speedometer is way off, and I need to know what rearend I have and possibly what gear ratios it could have in it. It supposedly has a factory ratio for an 86 IROC with this specific rear. I just bought this car as it is so I have no clue what was in it, or what it has now. I am new to 3rd gens, I had a 4th gen LS1 car before that I heavily modified, so I am no stranger to everything, just some miscellaneous 3rd gen info, like this.

 

Welcome to TGO. Check this link for possibilities:

https://www.thirdgen.org/1986-chevy-camaro

To make sure, jerk the diff cover and look: numbers are stamped on the ring and pinion:

41 : 15 = 2.73
41 : 14 = 2.93
40 : 13 = 3.08
42 : 13 = 3.23
41 : 12 = 3.42
41 : 11 = 3.73

If you have a T-5 check the sticky at the top of the page for drive and driven gears.

JamesC

 

There is a way to determine the ratio without popping the cover, but new fluid is a good idea.
Calibrating your speedometer isn't a problem, either. I have the complete list of GM part numbers for the 700R-4, so if you'll post your new ratio and your tire size, I'll give the part numbers needed.