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Old 05-10-2019, 11:05 AM   #1
MikeB
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Location: North Texas
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power brake master cyl bore and booster diameter

I'm looking to convert my 82 C10 short bed to power brakes, and would like to use GM or exact replacement parts.

The truck's factory setup was JB1 manual brakes with 1.0" thick rotors on the front and 11" x 2" drums on the back. A while back I installed dropped spindles and the thicker 1.25" rotors, so I essentially have JB1 brakes with better heat dissipation (and larger inner wheel bearings) on the front.

Looking at the factory brake specification chart, what I want to do is upgrade to JB3 specs. The JB3 power master cylinder has a bore of 28.6 mm (1.125"). My JB1 manual master cylinder has a 25.4 mm (1.0") bore. So that's pretty straightforward.

How about booster? The GM spec table shows "240S". But what is its diameter? And is it dual or single diaphragm?

I assume I'll need a different pedal pushrod, but are there any changes to the pedal ratio? In other words, is all the under-dash linkage the same for manual and power?

Thanks.
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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!
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Old 05-11-2019, 12:55 PM   #2
MikeB
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Join Date: Jul 2000
Location: North Texas
Posts: 3,597
Re: power brake master cyl bore and booster diameter

Found this at O'Reilly Auto Parts. More expensive than RockAuto, but I can easily return it and it has a lifetime warranty.

BrakeBest 50-1140

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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!
MikeB is offline   Reply With Quote
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