3500 rotor swap 71 to 77 ????

[old Chevy guy]

Ive been trying to get the rotors to put dual wheel rims on the front of my truck for some time. Its only a 71 c 20 but its heavy duty and I have swapped over to rear duals long ago. It has a Stake body dump on it. Ive tried to buy several rotors off trucks being parted but could never work out the shipping with the sellers. Today I was at the local junkyard and there was a 77 c 30 in the pile with practically new rotors on it. Does anybody know if the 77 3500 uses the same rotor as the 71 if it was a 3500 or a C30. I tried to look it up on some part sites but I cant find the rotor listed for the 71 with a dual option. However its the same part for 77 and 71 with single wheels if that means anything. Im sure I could buy them for a song but it wont do any good if its not the right part. It wont be there long before it goes to the shreader either.

[old Chevy guy]

ttt nobody knows this ? I thought for sure somebody would reply within minutes.

[viking427]

Your 71 3/4 ton C20 spindles are setup for 1.25" thick rotors and the "dual pin" floating style calipers. Assuming the 77 C30 in the scrap yard is a dually pickup truck ..which I assume it is and the reason why you want those extra deep front rotors... then its likely to have the larger 1 ton 1.50" thick rotors and "wedge" style calipers, which won't work on your C20 spindles. However, lots of years to mix and match parts by frugal owners, so the sure way to tell is look at the calipers - if they're "dual pin" floating style, then they're 3/4 ton 1.25" thick rotors and will fit your spindles. If not, then they won't. You can always grab the entire 1 ton rotor/caliper/spindle assembly off the yard truck - that'll give you true 1 ton stopping power up front.

[old Chevy guy]

Thank for the info. So will the spindles from the 77 fit on my 71? I actually have a 1 ton parts truck also that's a 72 but I sold the rotors off it years ago way before I ever had this dump truck. So what I really need to know I guess is are the rotors the same 1 ton to 1 ton 77 to 71 more so than if they fit on my C20. I know that the control arms and the ball joints are the same from the 71 C20 to the 72 C30 so it follows the spindles with fit from the 72 ,1 ton to the 71 ,3/4 ton.

[viking427]

Chances are no. That 77 C30 1 ton Dually truck in the scrap yard most likely has JL8 equipment on it (1.50" thick rotors + "wedge" style calipers). Your 71 spindles are designed to use dual pin floater calipers - which can only accomodate a 1.25" thick rotor maximium. The big JL8 equipment didnt come out until 1974. The 1971-73 3/4 ton C20 & 1 ton C30 front disc braked trucks all used floater calipers and 1.25" thick rotors. So your solution is to just pick up a set of 71-87 3/4 ton C20 rotors to mount on your 71 3/4 ton C20 front spindles. But if it were me, Id grab that entire 77 JL8 front disk setup including its spindles - you converted your C20 to a 1 ton dually rear for a reason, better to have heavier duty 1 ton front equipment to match it. Both types pale in comparison to the size of disk hardware on todays trucks.

Yes both 3/4 ton and 1 ton spindles will mount on your current C20 A-arms and ball joints. There were a few small running changes in the 71 -73 front disc equipment, but I dont remember the details ..1 pc rotors vs. 2 pc rotors etc. I always stayed away from 73 and earlier C20/C30 disc parts for this reason and its always been eaiser & cheaper to find 74+ disc parts anyway.