you want to change your 5X5 bolt pattern on 73-87 disc to 5X4.75

[502tripower]

Now we all know that the 73-87 front crossmember and suspension components can be swapped into the 60-72 trucks. The 73-80 Chevrolet C10 pickups used a 1.28 rotor. Then in 81-86 GM switched to a 1" rotor. I did a bit more digging and found that the calipers are different for the 1" rotor but use a common bolt pattern with 73-80 so, it looks as if the 91 Camaro rotor will work on the 73-86 spindles if the 81-86 calipers are used as well. Also the flexible brake line will need to be changed if you have the 73-80 caliper as one of the calipers uses American standard thread and the other uses a metric thread. The parts house could not tell me which one used what thread but that they were different. I will figure that out when I purchase the parts. I have not done this yet but it does look like it will work. fones1966 a member here PMed me telling me about this possibility and I want to thank him for that. I just thought I would post this information in case there were others that could use it. Olympic Brake here in Washington is who provided this information. One note I want to point out is the specs that I have all show the same bearings on all three rotors. I was told by fones1966 that the 73-80 1.28 rotor used a A-5 inner bearing so that bearing would have to be replaced when switching to the Camaro rotor but, what I found was the 73-80 heavy duty 1.28 rotor used the A-5 inner bearing and the 81-87 light duty rotor used the A-6 as shown in the specs I have provided. I hope this information is helpful. Here are the specs on both the truck and Camaro rotors:

73-80 Truck rotor specs are:

Height 4.88
Diameter 11.85
Min. Thickness 1.220
Hub 3.06
Outer bearing A-3
Inner bearing A-5
Seal Part # 8871
Bolt Circle 5X5

81-86 Truck rotor specs are:

Height 4.63
Diameter 11.86
Min. Thickness .96
Hub 3.20
Outer bearing A-3
Inner bearing A-6
Seal Part # 8871
Bolt Circle 5X5

91 Camaro 1LE Performance Package rotor specs are:

Height 4.65
Diameter 11.85
Min. Thickness .97
Hub 2.78
Outer bearing A-3
Inner bearing A-6
Seal Part # 8871
Bolt Circle 5X4.75