will a 98 firebird rear end fit into a 91 Camaro?

Im on the verge of buying a 98 firebird rear end with disc brakes and a posi unit...I understand that the posi unit is for a 28 spline...is it also a 7.5 like the 91? can I use the rear disc brakes for my 91? or can I simply swap out the two units? what about the shocks or springs?

Should swap out fine. But by doing so, your rear tires will stick out past the fenders. Would be a great time to get some 1 1/4" adapters to put on the front hubs, and use some 4th gen rims instead.

Or you could just keep your current rear end, and just swap the brakes onto that, and swap out the differentials.

I believe you may also want to check if the rear end your wanting to get came from a car that had traction control. If it did, it will have 2 separate brake lines going to each rear caliper. In which case, you will have to cut off the end of the lines and put on a T fitting so the lines merge into one, so that you can hook it up to your current brake line. If the car didn't have traction control. It shouldn't be as difficult.

There are also some issues with the ABS setup. Here's a nice page with some good information on these issues:
http://www.funkz.net/firebird/rearendfaq.htm

If I were to guess, your current rear-end would be very similar to the first 2 rear-ends discussed on that page.

>>Moved to Suspension and Drivetrain (http://www.automotiveforums.com/vbulletin/forumdisplay.php?f=2176)

chevyrulespops, I'm also going to have to ask you to please refrain from posting the same thread more than once. You made 3 identical threads in the Firebird, Camaro, and Problem Diagnosis forums. That's not necessary. One thread is enough, and as you can see, the proper location for it is in the Suspension and Drivetrain forum. Thank you.