thoughts on master bore size? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

oldtrux · 10-20-2021, 07:59 PM

i'm trying to decide on 1'' or 1-1/8'' bore size?
disc/drum setup.wilwood 2 piston d52 calipers
8 inch dual diaphram booster
regular compression 283
attention brake guru guys!
thanks Dan

**The Rocknrod** · 10-21-2021, 04:26 AM

With manual I'd go with 1". With power I'd go 1-1/8". Don't forget to re-drill your brake pedal arm.

**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!

SkinnyG · 10-21-2021, 10:29 AM

What's the difference in pedal ratio between power and manual brakes on these trucks??

oldtrux · 10-21-2021, 11:09 AM

Great info guys!! Thank you very much.

**The Rocknrod** · 10-21-2021, 11:40 AM

Quote:

Originally Posted by SkinnyG

What's the difference in pedal ratio between power and manual brakes on these trucks??

I used this - https://techtalk.mpbrakes.com/how-to...ng-pedal-ratio

10-20-2021, 07:59 PM	#1
oldtrux Registered User Join Date: Jul 2010 Location: Bancroft, ontario Posts: 555	thoughts on master bore size? i'm trying to decide on 1'' or 1-1/8'' bore size? disc/drum setup.wilwood 2 piston d52 calipers 8 inch dual diaphram booster regular compression 283 attention brake guru guys! thanks Dan

10-21-2021, 04:26 AM	#2
The Rocknrod Moderator Join Date: Aug 2011 Location: China Spring, TX Posts: 7,280	Re: thoughts on master bore size? With manual I'd go with 1". With power I'd go 1-1/8". Don't forget to re-drill your brake pedal arm. __________________ Master Chief, US Navy, Retired 1964 C10 Step-side Short Bed - In Progress 2009 2500HD Duramax LTZ 1948 GMC Panel 1956 Big Window Stepside 1953 5 Window Chevy Stepside 1932 Coupe New Seat Foam for Bench Seats?

10-21-2021, 08:33 AM	#3
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,597	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 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, recent 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 24 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.

10-21-2021, 10:29 AM	#4
SkinnyG Registered User Join Date: Feb 2012 Location: Beautiful BC, Canada, eh?! Posts: 2,270	Re: thoughts on master bore size? What's the difference in pedal ratio between power and manual brakes on these trucks?? __________________ 1961 Apache: "Grabber Orange" Shortboxed, pancake, step-notch, air-ride, turbo, LS 1977 Silverado: Shortboxed & dropped, potato-potato V8 Pontiac Firefly (Chevy Sprint): The ultimate engine swap: 5.7L in a 1.0L bag Lotus Super 7 Replica: Scratch-built street-legal rollerskate

10-21-2021, 11:09 AM	#5
oldtrux Registered User Join Date: Jul 2010 Location: Bancroft, ontario Posts: 555	Re: thoughts on master bore size? Great info guys!! Thank you very much.



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