Power brake booster leak?
Thread Starter
Racer
Joined: Apr 2012
Posts: 257
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Power brake booster leak?
My 76 has developed a slight hissing sound from under dash area when I apply the brake at an idle, such as in a parking lot or at a stop light. When this happens I loose the power assist, the pedal gets very firm. There are no leaks under the hood, my vacuum has always been marginal about 12 mmhg due to cam upgrade, but his situation is new. Could the booster be bad?
thanks,
Mike
thanks,
Mike
Race Director
Joined: May 2006
Posts: 18,742
Likes: 2,583
there is supposed to be a noise filter where the brake pedal push rod goes through the firewall to the booster. Other than the noise has the pedal always been hard due to the cam?
http://willcoxcorvette.com/advanced_...eywords=filter
http://willcoxcorvette.com/advanced_...eywords=filter
Race Director
Joined: Apr 2009
Posts: 19,294
Likes: 2,754
From: Charlotte NC
You should always hear the "whooshing" sound when you apply the brake pedal when the engine is running supplying vacuum to the booster. Some may be louder than others...but the sound should be there.
Also...another test...pump the brake pedal and expel all the vacuum from the booster. While maintaining the pressure on the brake pedal...crank the engine. If the pedal goes down a little bit...then this is a sign the the booster can be OK. NOT A DEFINITIVE TEST...but it is a fast test I do before using other test procedures.
If when you are applying the brake...the effort feels very hard and the pressure required is excessive...and you feel like the brakes are trying to stop a freight train...then YES...your booster is bad and can be re-built.
Also...if you disconnect and cap the vacuum hose to the brake booster and it feels the same as when it is attached...that is for sure a confirmation that the booster is bad.
In a rare case ...I had the check valve in the booster be defective and made it feel like the booster was bad...when actually it was not. All I did was replace the check valve and everything was perfect.
Rebuild the booster you have...especially if your oil dip stick is on the driver side of the engine.
"Booster Dewey" can do it...and he is out in Oregon/Washington state area.
DUB
Also...another test...pump the brake pedal and expel all the vacuum from the booster. While maintaining the pressure on the brake pedal...crank the engine. If the pedal goes down a little bit...then this is a sign the the booster can be OK. NOT A DEFINITIVE TEST...but it is a fast test I do before using other test procedures.
If when you are applying the brake...the effort feels very hard and the pressure required is excessive...and you feel like the brakes are trying to stop a freight train...then YES...your booster is bad and can be re-built.
Also...if you disconnect and cap the vacuum hose to the brake booster and it feels the same as when it is attached...that is for sure a confirmation that the booster is bad.
In a rare case ...I had the check valve in the booster be defective and made it feel like the booster was bad...when actually it was not. All I did was replace the check valve and everything was perfect.
Rebuild the booster you have...especially if your oil dip stick is on the driver side of the engine.
"Booster Dewey" can do it...and he is out in Oregon/Washington state area.
DUB
