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Discussion Starter #1
This car was just completely restored (not by me) and the front power disc brakes locked down. I bled some brake fluid from the right front wheel and the brakes released. I am assuming that the porportioning valve is stuck and needs cleaning. Is this correct? Thanks. . Dan Kuss
 

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It sounds like you may have a drum brake master cylinder with a residual pressure valve in it.
 

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Is the clevis pin adjusted correctly? Same theory as the residual pressure valve keeping pressure in the lines.

Are the calipers new, rebuilt??

Combination valves rarely (I've never seen one fail) are the culprit and are often blamed when the obvious needs to be checked first.

What about your flex lines? Are the new? Have they collapsed keeping pressure in the calipers??

Check the system over and make sure the the "little" things haven't been over looked.

Good luck!
Joe
 

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Did the brakes ever work correctly? If this is a reaccuring issue check to see if there is free play between the power booster and mastercylinder. Also check for freeplay at the pedal. If the master is slightly depressed the fluid can bleed down after the car sits but when you drive and use the brakes a few times the pressure will build and lock the brakes. I have seen this problem quite a few times when someone has replaced the mastercylinder and not known that there is a freeplay adjustment. Also if the master has been replaced the master cylinder piston may be incompatable with the pushrod and depressing the piston in the master cylinder.
 

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Discussion Starter #5
Originally posted by Slo307:
Did the brakes ever work correctly? If this is a reaccuring issue check to see if there is free play between the power booster and mastercylinder. Also check for freeplay at the pedal. If the master is slightly depressed the fluid can bleed down after the car sits but when you drive and use the brakes a few times the pressure will build and lock the brakes. I have seen this problem quite a few times when someone has replaced the mastercylinder and not known that there is a freeplay adjustment. Also if the master has been replaced the master cylinder piston may be incompatable with the pushrod and depressing the piston in the master cylinder.
 
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