Old 03-19-02, 05:34 AM
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94 GMC Sonoma,4WALBrakes,,peddle bottoms out slowly , iv'e changed the master cylinder , twice,bench bled the cylinder before installing, all wheel cylinders r good, i have a good hard peddle with engine off, engine on, peddle bottoms out , i pulled a vacuum on the booster, it wouldnt hold a vacuum, getting ready to change combination valve,, any advice, please help!

Last edited by jeff41; 03-19-02 at 06:01 AM.
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Old 03-19-02, 05:56 AM
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The year and type of vehicle is a start....

Did you bench bleed the master cylinder?

Are you getting a full and steady stream out of all the wheels?

Any leaks in the system?
Old 03-19-02, 09:54 PM
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Master Cyl

Where did you get the master Cyl? Is it new our rebuilt? You do know this is the symtom of an internal leak in the Master Cyl don't you. I have gotten so mad at rebuilt parts in the last 10 years I just don't buy them anymore.

In fact I still have to do something to make the parts fit, or finish up the job on even the new parts I buy.

Having a bad boster or check valve would not act like that. If you got a rebuild from a place like Pep Boys, Advance Auto or Auto Zone well it could be so out of spec that it could have an internal leak.

A little more info would help. Marturo
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