Hey Gang,
I have access to these two rear ends that are posi and disc brake compared to my open and drum brake rear end i have on my 91 RS.Here is the ads.

Chevy camaro rear posi differential with disc brakes off a 87 iroc. good condition must go $250

and then this one

1989 CAMARO positraction disk brake rear end, complete, $250.

I used the search button and didnt have any of my questions answered so i hope someone can help me out..

First does it have the same bolt pattern and is it a complete bolt in???THanks in advance

 

Both will bolt up fine.
The deciding factor would be the gear ratio of the rears.
Another factor to consider is the 89 rear has 28 spline axles while the 87 should have 26 splines. 88 or 89 is when they changed spline count. 28 is stronger.

 

so do you reconmend getting the 89?

 

Ok i got some info on the rear end,its from an 85 iroc and has 3:23 gearing.Is this a complete bolt on?Also does anyone know what ratio i have on my 91?Also is it a posi in the 85 and how big are the disc brakes.He says he has a couple and has a sale on them for 150 bux

 

Zepher:

YOU ROCK! I've have been looking all over for someone who knew when the spline count changed! Many thanks!

 

Rear ends from 82-2002 will all bolt up fine. 93-2002 rears will make your thirdgen wheels stick out a bit, but if you plan on getting a set of the newer wheels, this is the best way to go since you get batter brakes and gears ratios and don't have to run spacers on the back.

Your RS can have 2.73, 3.08, or 3.23 gears, it all depends on the tranny on the cars options.
The 85 Iroc rear should have Posi and the brakes are 10" or so.
I never measured my brakes. I swapped to LT1 brakes a couple of years ago and now I have LS1 brakes on the car.

 

Maybe this will help:

http://www.ws6transam.org/10bolt.html
http://www.ws6transam.org/1LEbrake.html#1LErear

Click 'em fast, because I may be pulling the plug on the website this month due to lack of money, time, and interest.

The quick answer is that either option will work, but you will be better served with the bigger, more reliable aluminum calipers that are found on the 1991 axle assembly. They are for all intents and purposes fully interchangable as I proved when I installed a 1999 SLP Firehawk heavy duty Torsen differential, 1991 rear discs, and 28-spline aftermarket axles into my 1984 axle housing.

--Dan