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Nice marmot.
 
mike_dunn's Avatar
 
Join Date: Jul 2007
Location: Daytona Beach, FL
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Soft brake pedal with engine running

With the engine off I can pump up and get a hard pedal, can't reach the floor with it. Engine on the pedal drops and becomes wimpy with lots of travel and no back pressure and pumping it does nothing. I can even slam the pedal to the floor while cruising and not lock the brakes. I've bled and bled and bled with super blue (using speed bleeders and old fashioned method) til I see no micro bubbles, the pads are seated firmly on the rotors, and there aren't any leaks. Is it trapped air or maybe a faulty master cylinder? Before I drop any $ anything else I should check?
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Mike Dunn
Daytona Beach, FL
1982 PORSCHE 911SC
Old 04-20-2009, 03:29 PM
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What was your bleeding sequence? Did you bleed farthest fitting out from the MC to closest?
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Old 04-20-2009, 03:33 PM
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Nice marmot.
 
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Yea followed Bentley manual, RR-LR-RF-LF. Used a mallet on the calipers too.
Old 04-20-2009, 03:57 PM
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Did you figure out the problem? Was it the M/C?
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'88 Carrera Coupe
Old 06-24-2009, 06:36 PM
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I am assuming you did not let it run out of fluid at any time. That would require a bench bleed of the MC.

Pump up the pedal with the car off, then with pedal firm start the car, pedal should drop a little and stay firm (this is the power assist working right). If pedal does not move you have a bad power assist. If power assist ok then it sounds like bad cup seal in the master cylinder and a rebuild or replace is needed.
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1968 911S "Leona"

Air goes in and out, blood goes round and round, any variation on this is a bad thing.
Old 06-25-2009, 02:46 AM
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4G1 4G1 is offline
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could it be a vaccum issue?
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Old 06-25-2009, 06:38 AM
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Quote:
Originally Posted by 4G1 View Post
could it be a vaccum issue?
That is what the boost check will find out. If there is no vacuum then there will be no sinking of the pedal. Then you just troubleshoot the boost system (hose connected and with vacuum, fittings etc. ok) If vacuum is getting into booster then the diaphragm is blown and the booster needs replaced.
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1968 911S "Leona"

Air goes in and out, blood goes round and round, any variation on this is a bad thing.
Old 06-25-2009, 07:12 AM
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