Master cylinder help in Hawaii

steveh said

Mike,
It builds up pressure with pumping...so I "think" the MC is good.

Just cant help but think that maybe the bore on the SSBC MC which was designed for KH 4piston calipers aint pushin enough fluid to make the single piston calipers function properly.

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MC's do not have a check valve, so pumping the pedal does not inherently increase the pressure. Air in the system would not be overcome by multiple pumps, so I doubt you have air. When pumping does help is when there is a leak in the MC piston seal, so it can't hold pressure. I had that with a recently installed MC (single pot). Pulled the piston out and found the seal had been cut by a sharp edge in the bore left after the rebuilders honed the bore and didn't file the ports smooth.

I doubt the single piston caliper has more piston area than 2 pistons of the KH 4-piston caliper. You could measure them and calculate. The piston area determines the final force on the pads, for a given pedal effort. What determines the volume required is both the piston area (rel. to MC area) and the free travel in the pads. Calipers have very little travel since they don't have a retract spring and rely on the twisting of the square O-ring seal to pull the pads back. I doubt the MC's used with K-H and with later calipers varied much in bore diameter. Usually the difference is between manual and power MC's.