79 El camino rear brakes not working

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rfoll
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79 El camino rear brakes not working

Post by rfoll » Wed Sep 12, 2018 8:08 pm

When I got this car the brakes were shot. When I hit the brakes, the left rear wheel would lock up but the right did nothing. I put new rotors and pads on the front, and new cylinders and shoes on the back. I pressure bled the system from the master cylinder to remove the nasty old fluid and remove air. Now the rear brakes don't work at all. I re-bled the system again and had someone apply the brakes while I opened the rear bleeders. It squirted fluid like one would expect, indicating the master cylinder was pumping fluid. There is no air in the lines. I saw a bleeder tool online that you install in the proportioning/combination valve to keep it stationary while the system is bleed. Is it possible that the internals have shuttled to one end and and not returned to center or something of that order? If so, can it be corrected? The warning light works while the bleeding is happening, but goes out when the job is finished. Finding a stock replacement is difficult, everyone wants to sell you a generic piece that requires adapter fittings. Curiously, my 71 C20 does nearly the opposite, It locks up the rear brakes until it has been driven for a few stops. What is the likelihood that these things can be successfully disassembled and cleaned up? Thanks, Rick
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BigBlocksOnTop2
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Re: 79 El camino rear brakes not working

Post by BigBlocksOnTop2 » Thu Sep 13, 2018 10:45 pm

Rig up a pressure gauge and see what the psi is. Is the master cylinder new. You said removed nasty old fluid. It could be an internal leak in the master cylinder from corrosion ( brake fluid is hydroscopic and will take on moisture). Gravity bleed while maintaining level in the master cylinder starting with the wheel cylinder that is the farthest from master cylinder. I myself have been down the road and thought I had all the air out. It is easy to aerate brake fluid. Gravity bleed wont aerate. Hope some of this helps.

rfoll
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Re: 79 El camino rear brakes not working

Post by rfoll » Fri Sep 14, 2018 10:49 am

I have been using a pressure bleeder to bleed the system, about 10 psi seems to do the trick. An internet search told me that the prop valve will indeed shuttle and hang if the system sees a loss of fluid at the rear. The rear slave cylinders were leaking some, and sure enough when removed the valve was stuck to shut off the rear system. What I don't understand is how I could bleed the rear in that situation. I replace the prop valve with a new one, and the problem persists. I am at a loss here.
So much to do, so little time...

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