Hissing Brake Booster When The Pedal is Up

[IntegratedTJ]

Title says most of it. My brake booster (or somewhere in there) is hissing at all times except when the pedal is down. When I kill the engine, all the vacuum in there just sprays out for a good 1-2 seconds. Is it the brake booster pushrod boot or the booster itself or what? Thanks in advance.

[cdowns]

i'd first check the rubber hose going ton the booster and make sure it is tight

[IntegratedTJ]

checked it. I figure the same thing and clamped it on. It's tight. I am now thinking that I improperly installed my new master cylinder.when I push the pedal just a tiny bit, the noise stops. I figure the push rod needs to be shimmed further in to the MC?

EDIT: The noise is coming from where the MC and brake booster meet.

[toolboxchev]

Spray it with soapy water, if you see bubbles, its bad and needs replacement.

As far as I know, nobody my makes one with a silicone or alcohol resistant material. I am on 3rd one with a lifetime warranty.

Ask me how I know.

[mike16]

I have had hissing brake booster problems before. the fittin that goes from the rear of the carb or intake could be stripped or cracked. the hose itself could be dryrotted and cracked. the plastic fitting on the booster could be broken or cracked. the rubber grommet in the booster housing could also be dryrotted and cracked. the booster halves and the diaphagm itself, between them could be dryrotted or cracked and leaking.

parts vendors can solve alot of the above problems. if the booster itself is defective, you may want to shop hemmings to have it rebuilt. you wont get the same quality from generic parts sold by auto parts stores. Maybe a good time to do a new msster cylinder too.

[CastIron]

It sounds like you need a booster. That is a symptom of a leak in the firewall side of the booster.

[Bigdav160]

What CastIron said. That's how brake booster work. When you step on the pedal it dumps the vacuum on inside portion of the booster. Sounds like that valve went bad.