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Old 05-10-2019, 11:05 AM   #1
MikeB
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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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82 C10 Custom Deluxe SWB -- original paint, 355/TH350, Vortec heads, GM RamJet 350 roller cam
69 C10 LWB -- Bought in 1989, now my son's http://67-72chevytrucks.com/vboard/s...d.php?t=775449
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 19 years! This is the very first car/truck Internet forum I joined.
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Old 05-11-2019, 12:55 PM   #2
MikeB
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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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82 C10 Custom Deluxe SWB -- original paint, 355/TH350, Vortec heads, GM RamJet 350 roller cam
69 C10 LWB -- Bought in 1989, now my son's http://67-72chevytrucks.com/vboard/s...d.php?t=775449
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 19 years! This is the very first car/truck Internet forum I joined.
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