I bought a 3.23:1 disc brake posi rear for my 1991 Z28. The rear is out of a 1991 GTA.

Anyway; The seller told me that the rear needed rotors and was otherwise complete. I bought it at night and didn't get a clear look at it. Well; come to find out that one of the caliper mount brackets (not the axle backing plate) was missing - The seller promptly stopped responding to my messages... go figure.

Anyway; Since I needed rotors as well as the bracket ($70 alone), I found a complete rear disc setup from a 1997 Z28 that I am trying to swap over to this 1991 GTA rear. The calipers and caliper brackets are identical. The only differences I see between the two setups is:

(a) E-Brake stuff is slightly diff (I'm going to use the 97 stuff since I've got the cables, too)

(b) The 1997 backing plates are like 3x thicker than the thirdgen stuff.

(c) The 1997 rotors have a slightly different shape to them where they meet the axle hub.

That being said, I can't figure what is going on here. At first, I thought I'd just remove the stock backing plates, and mount all of the 4thgen stuff (including the rotors).

The thicker backing plate is too thick and doesn't allow much of ANY room between it and the rotor (at least not enough for the caliper to bolt on).

I went back the thirdgen backing plates and attempted to bolt the calipers on, over the 4thgen LT1 rotors. For whatever reason, the rotor is VERY close to the inner-most area of the caliper and can't possibly be right.

I can only imagine that the mounting hub/flange on the 4thgen axles are further out than the 3rdgens (yes, I realize they are ~2" longer overall, but I'm talking how far it comes out of the rear end housing ends.

Any ideas? I thought I could run all this 4thgen stuff w/o an issue on this 10 bolt??