Poor brake pedal

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Dec 12, 2004 | 08:49 PM

jims6t6

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Joined: May 2004

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From: Knoxville, TN

Poor brake pedal

I have a 1995 F250 4X4. Recently I replaced the Master Cylinder. Without the engine running the pedal is rock hard and very high. As soon as the engine starts the pedal sinks almost to the floor. Have checked all wheel cylinders and calipers and have no leaks. The fluid level remains full. Is this the symptoms of a bad booster?

Dec 13, 2004 | 10:09 AM

ddbuggins

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Joined: Nov 2004

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did you bleed them? It is possible the booster is faulty. Take a can have someone pump them up and turn bleeder screw until you get steady steam of brake fluid.

Dec 13, 2004 | 10:15 AM

jims6t6

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Joined: May 2004

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From: Knoxville, TN

Did I bleed them

Bench bleed the MC and bleed all four wheels until nice new clear fluid came out. Don't believe there is any air in the system.

Dec 13, 2004 | 10:54 AM

SoCalDesertRider

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Joined: Dec 2002

Posts: 3,959

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From: USA

That sounds like either a master cyl leaking internally, or air in the system. If the booster has a vacuum leak, it should be hissing when you step on the pedal and the pedal should still be hard with the engine running since the booster doesn't have the oomph to push hard enough on the master cylinder. Sounds like the booster is doing it's job but the hydraulic system isn't holding pressure.

Dec 13, 2004 | 11:03 AM

stepman

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Joined: Dec 2002

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From: peoria, az

If your pedal stops before it hits the bottom and it holds there without slowly sinking further than, it sounds like there is still air in the system. I would keep bleeding. Sometimes it can take a while for the air to travel completely thru the line to get out the end. If, on the other hand, the pedal goes down a certain amount and then while holding pressure on it, it continues to sink, you would have an internal leak.