A friend of mine who's just paid a pretty penny to have his corvette restored called me out of desperation (you know how chevy guys hate to ask ford guys for help) because his newly restored vette had been poured over by several mechanics at the restoration shop for a day and a half, and still the brake pedal was soft.
They'd replaced the following:
Master cylinder (twice after suspecting a bad rebuild on the first)
LF caliper
Both front flex hoses from caliper to hard line
They'd bled the system multiple times using gravity, vacuum, and pressure.
I asked if they'd tried to isolate the problem to one wheel by plugging master cylinder or proportioning valve ports one at a time.
Yes - at least at the master - the problem appeared to be with the front, and likely the left front. (they used smooth jaw vice grips to pinch the rubber hoses to each caliper)
I asked if the red brake light was illuminated on the dash.
No - the light never came on.
At this point by a matter of elimination - the proportioning valve was about the only thing left.
The proportioning valve turned out to be the problem.
I would have leaned toward a new aftermarket adjustable piece - but being a "correct" restoration - they found a good used one in the shop - cleaned it up - problem solved.
My question is - what goes bad inside a proportioning valve? Is it something that can be "rebuilt" It's just a hydraulic piston with a couple springs and o-rings .... right?
They'd replaced the following:
Master cylinder (twice after suspecting a bad rebuild on the first)
LF caliper
Both front flex hoses from caliper to hard line
They'd bled the system multiple times using gravity, vacuum, and pressure.
I asked if they'd tried to isolate the problem to one wheel by plugging master cylinder or proportioning valve ports one at a time.
Yes - at least at the master - the problem appeared to be with the front, and likely the left front. (they used smooth jaw vice grips to pinch the rubber hoses to each caliper)
I asked if the red brake light was illuminated on the dash.
No - the light never came on.
At this point by a matter of elimination - the proportioning valve was about the only thing left.
The proportioning valve turned out to be the problem.
I would have leaned toward a new aftermarket adjustable piece - but being a "correct" restoration - they found a good used one in the shop - cleaned it up - problem solved.
My question is - what goes bad inside a proportioning valve? Is it something that can be "rebuilt" It's just a hydraulic piston with a couple springs and o-rings .... right?
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