'57 Power Brake Problem

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04-28-2014 | 11:42 AM

Indyhac

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'57 Power Brake Problem

I have a '57 Star Chief with the Treadle-Vac power Braking system that is not working correctly! I sent the booster and master cylinder unit to Midwest Power Products for rebuild but that has not corrected my problem. They insist that the unit was tested and working when it left their facility. My problem is that when applying the brakes, the pedal feels like power is being applied for about 3/4"-1" of pedal travel with little to no braking action then becomes a hard pedal at which point the brakes begin to take hold but without any power assist. At that time, the brakes work as though the booster is not working and I have to press the brake pedal extremely hard to get the car to stop. This would be very dangerous for a quick/emergency stop. Here is what I've done to try to correct the problem.(1(Checked vacuum at booster(-19) (2) Checked vacuum reservoir; holds vacuum in excess of 15 minutes. (3) Rebuilt all wheel cylinders, turned drums, replaced brake shoes. (4) Bled master cylinder and wheel cylinders. (Brake lines and flex hoses look to have been replaced by previous owner/look like new. (5) Adjusted shoes to light drag on drums; with car on jack stands and light pressure on brake pedal, shoes stop wheels so they cannot be rotated by hand. (6) Have centered shoes on drums per Pontiac adjustment specifications. At this point I am at my wits end; I have no idea what else to try to correct the hard braking problem. Any suggestions would be greatly appreciated!
Thanks, Scott