I noticed my rear axle is not centered when i got the car a few months ago but the rear end started howling so i swapped in the 4th gen rear end and now its a problem. I am using the stock iroc rims from my old 82 camaro and 235/60r15 tires but with the axle being shifted to the pass side it rubs on a bump. I dont see any frame damage so im at a loss as to why its shifted to the pass side almost an inch. This is a 1991 Chevy Camaro Z28 with a 5.7 and a 700r4 rear is an open end 3.83 gear with drums. All rear end linkage is stock...

 

If the car is lowered the rear will be off center. Take close look at the rear suspension and you will see how the ride height affects the centering of the rear end. You need an adjustable panhard bar to center it back up.

 

Cars ride height seems factory but i could be wrong ill have to order the panhard bar soon

 

The springs could be sagging. Does it have the spring isolators on the top?