Power front discs on a 57 Chevy my dad (since p***ed) built. I believe the spindles, calipers and proportioning valve are from an old square body Caprice. When the car was first built, the front brakes would gradually activate, stopping the car. Dad would get out, loosen the fitting at the M/C and go home. He finally got the brakes good enough to suit him, but I don't know how or how good the were, because I never drove it. Now I have the car, and the brakes are shade less than marginal. New pads, new M/C (the old one did leak just a liitle), bled it all, brakes still are poor. I have the H shaped tool to set the proper distance between the booster and M/C, am confident that is good. With the M/C removed, the booster rod travels about 3/4 of an inch. I don't think that's enough, but if I lengthen the brake pedal rod, I think that will cause the brake booster rod to go out, causing the brakes work. Short of replacing everything, I am stumped. I know this is most likely a simple fix, but I also remember a thread from a few years ago where things really got into the weeds with metric calipers and all kinds of stuff. I just want the dang brakes to work. Any thoughts?
Something to check, some years of Chevy used two different master cylinders on the same models. They were different brands but the big difference is that one has a shallow indent in the piston for the push rod and the other has a far deeper indent for the push rod. Back when I was doing brakes every day in a tire store I ran into that a time or two but after the first round of battle with it I always checked a lot closer before ordering the part. Checking OReilly's listing for my wife's old 79 Caprice ex cop car that she had way back when I see that they list the standard 1.125 bore and show a .94 bore master cylinder. Rock Auto just showed 1.125 bore.
With the brake pedal all the way against the brake light switch, you push the pedal and only get 3/4" of travel on the pushrod coming out of the booster? Is it an immediate reaction as soon as you push on the pedal? Or is it delayed?
@Lloyd's paint & gl*** there is a definite delay. The pedal travels pretty good ways before the rod coming out of the booster moves forward.
Apart from the tiny amount of free play between the pedal and the booster there's no source of delay within the booster itself as the input and output are directly connected. Youe covered the clearance between the booster and master, but what about the pedal and booster? To me, insufficient 'grab' on the brakes is most likely either a too large master diameter, or insufficient pedal ratio, or a combo of both. Checking the pedal ratio is quick, easy and free, as is checking pedal free play. Chris
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