power brake problem
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Postmaster
Joined: Dec 2002
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From: Southern Oregon USA
power brake problem
79 F150 2wd.
When I start it, the pedal draws down and holds some pressure on the brakes. Vacuum is hooked to a manifold vacuum source. Is this a symptom of a bad booster? I have never seen one do this before.
Jason
When I start it, the pedal draws down and holds some pressure on the brakes. Vacuum is hooked to a manifold vacuum source. Is this a symptom of a bad booster? I have never seen one do this before.
Jason
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Joined: Jan 2008
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Booster test:
Shut engine off
Pump brake until all vacuum has been evacuated
hold pedal to floor while starting engine.
what does the pedal do ?
RE: for reference on newer thread this has been linked to older thread.
Posts #20,23,25
https://www.ford-trucks.com/forums/4...t=booster+test
Shut engine off
Pump brake until all vacuum has been evacuated
hold pedal to floor while starting engine.
what does the pedal do ?
RE: for reference on newer thread this has been linked to older thread.
Posts #20,23,25
https://www.ford-trucks.com/forums/4...t=booster+test
Last edited by Mil1ion; Aug 29, 2006 at 12:22 PM.
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To test power booster, http://www.classicperform.com/TechBo...tm#testbooster
probably the diaphram in the booster is leaking.
Keep us posted of your results.
buck
probably the diaphram in the booster is leaking.
Keep us posted of your results.
buck
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Postmaster
Joined: Dec 2002
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From: Southern Oregon USA
Did all of the tests listed for the booster as well as tested the check valve. All check out ok. Pinched off vacuum source and the pedal returns as normal.
I'm guessing that the internal valving in the booster is leaking, which is causing it to assist even without the brake pressed. I've seen a lot of failed boosters, but never this way. I'm hoping that I have a spare something on the shelf that will work. I had a 76 parts truck a couple of years ago that I wish I had kept. I could have used a lot of parts from it for this project.
Jason
I'm guessing that the internal valving in the booster is leaking, which is causing it to assist even without the brake pressed. I've seen a lot of failed boosters, but never this way. I'm hoping that I have a spare something on the shelf that will work. I had a 76 parts truck a couple of years ago that I wish I had kept. I could have used a lot of parts from it for this project.
Jason
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That the way it seems it goes sometimes, you got all these parts sitting around, but then you let some parts go to friends or neighbors, and then it seems the part that was sold or donated is the part which is needed.
It does seem like the internals of the booster are worn.
buck
It does seem like the internals of the booster are worn.
buck
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Postmaster
Joined: Dec 2002
Posts: 3,594
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From: Southern Oregon USA
I swapped brake boosters with my 77 which cured the problem. There is a seal that holds off vacuum from the back side of the booster until the pedal is depressed. Vacuum was leaking by this seal which was pulling the pedal down to hold just slight pressure on the brakes.
Jason
Jason
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