Help! No Brakes


Old 01-28-02, 06:55 PM
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Question Help! No Brakes

1989 Plymoth Sundance- Had Broken Right front brake line, Master cylender emptied. Renewed front Brake line, replaced both rear cylinders and renewed and adjusted rear brake shoes(front pads 75%). Gravity fed all 4 brake lines. Here's the problem(ARE YOU READY FOR THIS?)
Start car brake pedal goes to floor. Turn engine off,pump up brakes(they hold) start car while holding brake pedal, pedal goes to floor. Disconnect vacuum line to power booster,start car, pump up brakes(they hold) reconnect vacuum line while holding pedal,pedal immediately pushes to floor. Renewed Booster check valve (same problem) Renewed and bench bled Master Cylinder(same problem).
Could it be the booster(never known one to go bad) or proportioning valve. Running out of money and ideas!
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Old 01-29-02, 05:23 AM
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Likely a bad master cylinder at this point.

Verify and double verify you have no hydraulic leaks.

A bad booster gives the opposite effect. The pedal will be rock hard.

If the pedal sinks to the floor, you have a hydraulic, not a vacuum problem!
Old 01-29-02, 06:15 AM
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Had this happen on an '85 Impala. Get another master cylinder. The one I used was bad out of the box, so I ended up doing all the work twice. Second master cylinder was fine.
Old 01-29-02, 06:54 AM
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Very true and I agree.
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