help
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Senior User
Joined: Apr 2005
Posts: 174
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From: south GA
help
i have a 81 f150 302 and when i dont have my foot on the bake it makes a hising sound 
but it stops when i put on brakes could anyone tell me what causes this and how do i stop it? thanks
but it stops when i put on brakes could anyone tell me what causes this and how do i stop it? thanks
Senior User
Joined: Mar 2004
Posts: 274
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From: MI
Inspect the check valve that plugs into the brake booster. Air should flow only one way through it. If it flows both directions its not keeping a vacuum on the brake booster. There may be other places that vacuum could be leaking but the brake is often over looked.
Post Fiend
Joined: Jul 2004
Posts: 8,786
Likes: 28
From: Northern California
Just to add The rubber grommet that seats and seals the check valve could be bad, as well as The brake booster itself can be leaking. there is a rubber seal inside the passenger compartment on the brake booster, that the linkage goes through. It could be leaking there.
just my two cents.
just my two cents.
Senior User
Joined: Oct 2005
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Usually if you hear the vacuum leak from inside the cab the booster is leaking and needs to be replaced. Dont wait too long as when the booster gives out all together breaking requires about a ton of weight on the pedal to make it stop and at high speeds this becomes a real problem!
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Senior User
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From: south GA
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Senior User
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dont remember I think you have to buy the master and booster all together could be around $200
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Post Fiend
Joined: Jul 2004
Posts: 8,786
Likes: 28
From: Northern California
You can buy the master and booster seperate or as whole unit.
If your brake fluid is dirty, or you have doubts about the master cylinder, then replacing it, changing the fluid, when you replace the booster is a good idea.
The booster or booster / master cylinder combination averages anywhere between $79 and $150 dollars depending on where you go.
While you are at it. Check the brake lines, hoses, wheel cylinders, pads, shoes, etc.. for damage, wear, leaks, cracks, etc...
While doing the master cylinder, and brake booster, it's much simpler to replace these components, and less work in the long run. Imo
good luck.
If your brake fluid is dirty, or you have doubts about the master cylinder, then replacing it, changing the fluid, when you replace the booster is a good idea.
The booster or booster / master cylinder combination averages anywhere between $79 and $150 dollars depending on where you go.
While you are at it. Check the brake lines, hoses, wheel cylinders, pads, shoes, etc.. for damage, wear, leaks, cracks, etc...
While doing the master cylinder, and brake booster, it's much simpler to replace these components, and less work in the long run. Imo
good luck.
Last edited by 81-F-150-Explorer; Nov 29, 2005 at 07:01 PM.
