Brake booster hissing

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Mar 5, 2007 | 04:06 PM

Ervin

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From: Medina, Ohio

Brake booster hissing

Ok I have 78 F250 4x4. Today I kept hearing a hiss in the cab. It is only when I put my foot down on the brake peddle. Does this mean a new booster or is it repairable or cheaper to rebuild The master was just a little low in the front. Or is it time to upgrade to the F350 master and booster? Thanks, Erv

Mar 5, 2007 | 04:24 PM

pcheyne

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I would replace it.

Mar 5, 2007 | 04:36 PM

Mil1ion

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Pressing the pedal..... With the engine is running or not ?

PEDAL

Peddle is to sell something.

Can you read this?

Last edited by Mil1ion; Mar 5, 2007 at 04:40 PM.

Mar 5, 2007 | 04:49 PM

Ervin

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From: Medina, Ohio

Sorry it was a long day. When I push down the pedal slow and the engine running. Seems to stop ok. But it makes the hiss sitting and holding the pedal. No Dennis, when I make it bigger it gets blurry. Can you give the a link to it? Also I have a vacuum gauge in the truck , I see it drop, but it holds pretty steady. Erv

Mar 5, 2007 | 09:16 PM

firstonraceday

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From: East Texas

Same thing happened to my 77. The booster is shot and could be allowing brake fluid to leak back into it. I just got a reman booster. So far so good.

Mar 10, 2007 | 04:15 PM

cletus t

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From: va.

sounds like the bladder bag in the booster has a small hole. better go ahead and change it. if it blows out completey you will still have brakes but not power brakes

Mar 10, 2007 | 04:22 PM

Torque1st

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When replacing the booster or MC replace both.

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Mar 10, 2007 | 07:31 PM

Mil1ion

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Booster diaphrams are known to go bad after 20 years. Thats why one should have a used booster from a wrecking yard inspected before it is installed.

Do the tests I posted above and know for sure.

Mar 10, 2007 | 07:37 PM

#10

Ervin

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From: Medina, Ohio

Thanks for the help guys. I am going to go get a new booster and master tomorrow. Dennis can you give me the part numbers for the up grade to the F350 booster? I would like to price it.Thanks, Erv

Mar 10, 2007 | 07:52 PM

#11

Mil1ion

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w/o speed control - FT-39 or 2512300 ...(12300) booster

Last edited by Mil1ion; Mar 10, 2007 at 07:55 PM.

Mar 10, 2007 | 08:13 PM

#12

Ervin

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From: Medina, Ohio

Thanks Dennis Erv

Mar 10, 2007 | 10:08 PM

#13

fasthauler

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From: Hesperia, CA

Definitely get that booster out of there. I let mine go too long and the #4 & #7 intake valves warped. The guy at the machine shop spotted it immediately. He said it is a common problem for the 460. The cold air going through the leaking booster goes straight into the #4 & #7 intakes. When the engine gets hot the cold air hitting those hot valves can warp them.

Mar 10, 2007 | 11:31 PM

#14

Torque1st

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The lean mix can also burn valves and hole pistons.

There is an internal seal that also goes bad frequently.

Mar 11, 2007 | 01:11 AM

#15

76 crew

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From: Kahaluu, Hawaii

with the engine off pump the brake pedal several times (maybe 5) to get all the residual vaccum (air) out of the system.

then hold the brake pedal down and start the engine the pedal should go down about an inch or so, if it does this its not your booster its something else.

when you step on the pedal with no vacuum assist (engine not running), its like manual brakes, as soon as you start the engine, the vacuum from the engine will pull on the diaphragm, and thus "helping" you push the pedal down, thats why it should drop a little more when u start the engine.

the other lazy man way is to clamp the hose coming from your engine and going to your booster. Does it get harder to push the pedal? then your setup is working, if you clamp it and brakes feel the same, then u been driving around with manual brakes and didn't even know it.