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Old January 17th, 2021, 01:53 AM
LordNatedawg LordNatedawg is offline
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Join Date: Sep 2019
Location: Sparks, Nevada
Truck: 1966 GMC 1500 Custom
Age: 21
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Default Re: "Papa Smurf" - 1966 GMC 1500 Custom

I don't like to jump the gun, but I think I solved the problem. I installed a new master cylinder. An OEM ACDelco meant for a 1979 GMC C2500 HD. Plumbed some new lines to the proportioning valve, bench bled the master, and then installed it. I also installed larger disc brake calipers because the old ones I had were meant for the light duty C25. Lots of air in my brake system, but the pedal is significantly stiffer and only sinks with some constant, heavy pressure. Quickly stomping the pedal makes it feel rock hard. I think once I get everything bled, I should have a solid brake pedal.

Really don't want to jump the gun or jinx myself, but I'm feeling good about this.
A 1/8" increase in bore size doesn't seem like much. But lets assume that the fluid is moving through a cylinder 8 inches long. A 1-1/8" bore and 8" stroke would push about 7.95 cubic inches of fluid. A 1-1/4" bore and 8" stroke would push 9.81 cubic inches of fluid. Now that's not exactly how master cylinders work, but it proves a concept. The volume adds up over distance.
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