hard brake pedal
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Senior User
Joined: Jan 2004
Posts: 238
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From: Eastern PA
hard brake pedal
97 F-350 PSD W/cruise......110k miles. Hard brake pedal feel after sitting w/ foot on brakes at traffic light , if I start to move forward I get hard pedal w/little or no braking left to stop. Brake warning light comes on, then goes off if I raise RPMs....best bet for remedy? Vacuum pump or power brake booster? Lemme know...............Thanks
Fleet Mechanic
Joined: Feb 2004
Posts: 1,816
Likes: 3
From: River Valley AR
My guess is the pump or tubing from the pump. After staying stopped at light pedal feels hard, but how did it feel when you first stopped?
Where I'm going is that your booster should have acheck valve in the big vacuum line. If the diaphragm and check valve are working, you could get a good pedal at first. However once that vacuum in the booster is lost, the pump should replenish it. If that is what's happening when yuo rev it up, your pump may very well be losing efficiency.
You can use some simple tests to help figure it out, or at least narrow it down....
Connect a vacuum gauge to your vaacuum system. Individually pinch off then release the vacuum hoses that go to the various other components. If you pinch one and you notice your gauge says more vacuum, you may have a leak or a bad component on that line.
You can cap off as many leads as possible and measure the vacuum that the pump is putting to the system.
A hand operated vacuum pump (Real good ones $50-$60) can let you put vacuum on individual components to check them. A vacuum pump in a good kit has about ten billion other good uses too.
Where I'm going is that your booster should have acheck valve in the big vacuum line. If the diaphragm and check valve are working, you could get a good pedal at first. However once that vacuum in the booster is lost, the pump should replenish it. If that is what's happening when yuo rev it up, your pump may very well be losing efficiency.
You can use some simple tests to help figure it out, or at least narrow it down....
Connect a vacuum gauge to your vaacuum system. Individually pinch off then release the vacuum hoses that go to the various other components. If you pinch one and you notice your gauge says more vacuum, you may have a leak or a bad component on that line.
You can cap off as many leads as possible and measure the vacuum that the pump is putting to the system.
A hand operated vacuum pump (Real good ones $50-$60) can let you put vacuum on individual components to check them. A vacuum pump in a good kit has about ten billion other good uses too.
Thread Starter
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Senior User
Joined: Jan 2004
Posts: 238
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From: Eastern PA
I replaced the vacuum pump over the weekend.....it's nice to have brakes again ! A word of advice to anyone else who does this....buy a replacement pulley($18.) to install on the new pump and make sure you have the bolts in the holes BEFORE installing the pulley on the new pump or you'll never get them in. No need to remove the fan or the fan shroud either.
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