The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - you want to change your 5X5 bolt pattern on 73-87 disc to 5X4.75

502tripower · 12-16-2008, 06:22 PM

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

12-16-2008, 06:22 PM	#1
502tripower Registered User Join Date: Jan 2008 Location: Satsop, WA Posts: 606	you want to change your 5X5 bolt pattern on 73-87 disc to 5X4.75 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 __________________ 1963' Chev Custom Cab 502, 67' 435hp 3X2 intake, 9" 4:30 Posi 1961 Impala SS 348/350 4-speed 3:70 Posi 1961 Bel-Air Bubble Top 283 Turboglide soon to have a 348 3X2 4-speed 1950 17' Fairliner twin cockpit barrel stern 312 Y block 1X1 intake Borg Warner 1:1 gear 1957 Fleetform 14' twin cockpit barrel stern 1969 BP-125 Merc 1949 Transitier 3-wheel forklift Crosley 4-Banger 98' FXD 2002 2500HD Last edited by 502tripower; 01-28-2009 at 02:18 PM.