Welp, I just bought a new differential. It's a 9bolt differential out of a supposed 87 Iroc. It does have POSI. The guy said it has moroso 3.42 gears in it with royal purple oil. If it is 3.23s, oh well I'm fine with that. I bought it because it is posi. It came with the rear disk plates that hole the calipers but nothing else. I ended up paying 120 for it.

So my questions are:

This will bolt right up to my 91 camaro I hope? Even though mine is a 10 bolt I believe.

Whats a ball park price for calipers, brake lines and proportional valves run each?

Did I get a good deal?

Any other tips or suggestions?

 

Crap. Below.

 

A 9-bolt will either have 3.27 or 3.45 gears. Unless your 91's rear has been swapped out at some point, the rear is a 10-bolt.

The 9- and 10-bolt are interchangeable. The combination valve that would accompany standard disc brakes on an 87 won't bolt to your 91, as the threads are different. However, since the rear doesn't have brakes, you could update to 89-97 PBR's and purchase the appropriate 1LE valve. The second link below is for a 10-bolt, but the only difference is the backing plates (which can be purchased from Ed Miller at http://www.flynbye.com/)

https://www.thirdgen.org/forums/faq-...iscs-89-a.html

Other considerations are the speedo drive/driven gears and the parking brake.

JamesC

 

Alright well looks like I am going to pull the cover because the lowest gear I want is 3.42s.

Would a 10 bolt rear disc set up work on a 9 bolt bw rear?

 

With the correct backing plates, yes. (The bolt pattern on the axle flanges/backing plates are different between 9- and 10-bolt.)

JamesC

 

The easiest way is to rotate the axle & count the # that the pinion spins. The 3.45 is the 9-bolt equal to the 10-bolt 3.42, so your fine there. And since the 9-bolt 3.27 (the 10-bolt 3.23 equivalent in ratio) is a higher gear, your fine there too since it is a higher gear & you didn't want to go lower.

 

Not enough difference between a 3:42 and 3:45 to notice. That 9-bolt is a little stronger than the 10-bolt, but it is hard to find parts for. Rear housings interchange freely between all third gen Camaros & Firebirds, besides the things that JamesC mentioned. Dean