Kingsport, TN29 posts · joined Nov 20251976 Chevrolet C10, 350, TH350
let me clear up the thing that is going to get said anyway, because i searched this to death before i posted. a 73-87 C10 already left the factory with front disc brakes. so when people say "drum to front disc swap on a square-body" they almost always mean one of two jobs, and i am tangled up in both this winter, so here is the real question for both.
one, my brother in law has a 1970 C10 with four wheel drums, and we want to put the 73-87 disc setup on the front of it. that is the actual drum-to-front-disc swap, the 67-72 onto later spindles. two, my own 76 has the factory front disc and rear drums and i want rear disc on it because i tow a small car trailer and the drums fade on the long grade down off Bays Mountain.
what i am trying to sort out before i spend money: on the 70, is it really a bolt-on of the 73-87 spindles, rotors and calipers, or does it drag the master cylinder, the combination valve and the booster into it. and on my 76, which rear caliper and bracket kit are people actually running that is not junk, and does a rear disc conversion need a different proportioning setup or does the stock combination valve live with it.
squarebody_frame_offRestorer#2
Amarillo, TX44 posts · joined Nov 20251984 Chevrolet C10, 350, 700R4, frame-off
i did the 67-72 front swap on a 69 longbed a few years back so i can speak to your brother in law's truck. the 73-87 disc spindles, rotors, calipers and the six lug hubs bolt to the 67-72 lower control arm and steering arm, that part is genuinely a swap. what gets people is the plumbing and the pedal, not the parts that hang on the spindle.
you have to go to a disc/drum master cylinder, the one with the bigger reservoir up front, and you need the combination valve for front disc and rear drum so the pressure splits right and the hold-off works. keep the 70 as disc front and drum rear for now and it is a clean, known setup, that is literally what every 73 up truck is. do not mix a disc master with no proportioning and expect it to stop straight.
and the booster. a four wheel drum truck has a small or no booster, so budget for the correct dual diaphragm booster for front disc or the pedal is going to be a workout.
ls_swap_or_keepWeekend wrench#3
Modesto, CA27 posts · joined Nov 20251987 Chevrolet R10, 5.3 LM7 swap, 4L60E
on your 76 rear disc question. i put rears on my R10 when i did the drivetrain and the honest answer is you do not need them for stopping, the stock front disc rear drum on these trucks will lock all four tires if the drums are adjusted and not full of dust. what rear discs buy you is they quit fading on a long tow grade and they are less fuss to live with, which is exactly your Bays Mountain problem, so i get it.
i ran a bolt-on bracket kit that uses a GM caliper off a later half ton and the matching rotor, and the big thing nobody tells you is the parking brake. a rear disc conversion needs either an internal park brake caliper or a separate cable setup, and the cheap kits make the park brake an afterthought. if you ever park on the grades around there you want that sorted, not a zip tie.
i left the stock combination valve and it stops straight, but i added an adjustable proportioning valve in the rear line so i could dial a hair of pressure out of the back. with the lighter rear disc you can get the back to lock early if you do not.
original_c10_longbedWeekend wrench#4
Pueblo, CO33 posts · joined Nov 20251986 Chevrolet C10 longbed, 305, TH350
before anybody spends a dime converting anything, service what you have. i chased a fading pedal on my 86 for a month sure i needed rear disc, and it was a collapsed soft line on the driver front acting like a one-way valve, plus rear shoes glazed hard as glass. new soft lines, fresh DOT 3, shoes and a drum, adjusted properly, and the truck stops like a different vehicle. forty dollars of rubber lines fixed what i was about to throw a 600 dollar kit at.
i am not saying do not do the rear disc, i am saying a 40 year old brake system that fades is usually a tired brake system first and a design problem second. do the boring stuff, then decide.
drum_to_disc_swapOPWeekend wrench#5
Kingsport, TN29 posts · joined Nov 20251976 Chevrolet C10, 350, TH350
original_c10_longbed wrotea 40 year old brake system that fades is usually a tired brake system first and a design problem second.
took this to heart before thanksgiving. my 76 had the original soft lines, cracked at the crimps, and the rear shoes were down and glazed. new soft lines all around, new wheel cylinders, shoes, drums turned, DOT 3, and a careful bleed. pulled the car trailer empty down off the mountain saturday to test it and the fade is gone. so the rear disc on the 76 is now a someday thing, not a this-winter thing, which freed up the budget for the brother in law's truck where it actually matters.
on the 70 we are going correct: 73-87 disc spindles and the six lug hubs, disc/drum master, the front disc rear drum combination valve, and the right booster, exactly as squarebody_frame_off laid it out. i am keeping it disc front drum rear like a 73 up truck instead of getting cute. for anybody searching this later, the federal brake standards these trucks were built to, plus the recall lookup, live over at nhtsa.gov, and it is reading that tells you what a safe brake job on an old truck is actually supposed to deliver.
obs_ford_f150Daily driver#6
Tulsa, OK21 posts · joined Nov 20251990 Ford F-150 XLT Lariat, 5.8 351W, E4OD
ford guy lurking on a chevy brake thread because the lesson is the same across the yard. my 90 F-150 had the rear drums and the same tired-system fade, and a soft line and a good rear shoe job fixed 90 percent of it. the other 10 was the combination valve on mine being partly stuck, which is the ford version of what you all are describing.
point being, whatever badge is on the tailgate, service the whole hydraulic system on a 35 year old truck before you convince yourself you need a kit. the kit is more fun to buy and the soft lines are what actually stop the truck.
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