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**MikeB** · 10-21-2021, 08:33 AM

With a decent size booster like yours and a stock engine making 18"-20" vacuum at idle, I'd say 1-1/8" would be the way to go. 1" might be a bit "grabby" with a booster and lots of vacuum, but you just never know on an aftermarket setup.

I'd skip the fixed "one size fits all" proportioning valve and install a manual valve in the rear brake line. I mean why reduce rear braking power if you don't need to? Start with the valve wide open, and then adjust if necessary to keep the rears from locking up before the fronts during a panic stop.

Also, install a 10psi residual valve in the rear line (after the prop valve) to keep the shoes close to the drums.

I'm not sure if I'd re-drill the pedal to reduce leverage. I did not do that when I converted my manual brake 69 C10 to power brakes back in the 90s. I do have to admit it is just a bit touchy, but I'm used to it.

I used a stock 71/72 booster & M/C along with spindles, brakes, and power steering parts from a mid-80s C10.

Just have to add that with those Wilwood brakes and pads, along with rear drum brakes in good shape, you could probably go with a 7/8" M/C with NO booster and stand the truck on it's nose!

10-21-2021, 08:33 AM	#3
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,425	Re: thoughts on master bore size? With a decent size booster like yours and a stock engine making 18"-20" vacuum at idle, I'd say 1-1/8" would be the way to go. 1" might be a bit "grabby" with a booster and lots of vacuum, but you just never know on an aftermarket setup. I'd skip the fixed "one size fits all" proportioning valve and install a manual valve in the rear brake line. I mean why reduce rear braking power if you don't need to? Start with the valve wide open, and then adjust if necessary to keep the rears from locking up before the fronts during a panic stop. Also, install a 10psi residual valve in the rear line (after the prop valve) to keep the shoes close to the drums. I'm not sure if I'd re-drill the pedal to reduce leverage. I did not do that when I converted my manual brake 69 C10 to power brakes back in the 90s. I do have to admit it is just a bit touchy, but I'm used to it. I used a stock 71/72 booster & M/C along with spindles, brakes, and power steering parts from a mid-80s C10. Just have to add that with those Wilwood brakes and pads, along with rear drum brakes in good shape, you could probably go with a 7/8" M/C with NO booster and stand the truck on it's nose! __________________ Mike 1969 C10 LWB -- owned for 34 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 23 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then! Last edited by MikeB; 10-21-2021 at 08:49 AM.