I don't want to pay $89 + $12 shippingand wait a few days to get a new Delco unit, so how do I flush and bench test the old one?
BudDBullitt said:Well, if you still have dirt/rust in your master cylinder, then I suspect a crudy caliper, wheel cylinder or brake line. Was one reservoir dirty or both? The reservoir nearest the firewall supplies the rear drums, the other one nearest the radiator, the front discs. This would simplify trouble-shooting, obviously. You then could disconnect one line from one caliper or wheel cylinder at a time and have someone depress the pedal. While this will introduce air into the system, you are already having problems, so it can't get much worse. If there is no dirt, then you can eliminate certain lines. Reconnect the lines and try to eliminate the caliper and wheel cylinder, to find the suspect part.
Another problem that would contribute to poor braking is a proportioning valve. You have to bleed the system first, then recenter the valve. I'm not sure which type of valve is equipped on your Chevy. There's one type mounted near the master cylinder and a conventional remote mount, like the one on Sharks. Some pick-up trucks and like models have a variable proportioning valve, called a pressure control valve or load-sensing, but it's the same thing. Here's the general procedure for Pressure Differential Valve (remotely mounted):
1. Fill the master cylinder and bleed the brakes.
2. Turn the ignition switch to "On" or "Accessory"
3. Slowly depress the brake pedal down and the piston should center itself, causing the brake light to go out.
This should reset the valve. If it does not, you will have to have someone depress the pedal as you open a bleeder screw. You have to immediately close it, as soon as the brake light goes out or you will have to repeat the procedure, using a opposite side bleeder, whether you tried the front or rear first.
If you have a master cylinder mounted proportioning valve, make sure that a new sealing washer is used. My tech manual suggests that if the valve is suspect, diagnosis should be done by a reputable shop. They give no instructions, otherwise. I hope this helps.