Hissing noise when i push in the brake pedal...

[xminnis]

I thought my brake fluid was leaking because i saw a little puddle in the garage but after further inspection i think that is actually trans fluid, the brake fluid is full, so what could the hissing be from? I thought master cylinder at first but the brakes are not pushing all the way to the floor and like i said the fluid is full

 

[dan2286]

Is your brake pedal really firm with the engine running? If so, it is probably a bad brake booster.

 

[xminnis]

no its actually a little more mushy or soft ,however you wanna describe it, than it should be but its not going all the way to the floor

 

[Geesie]

I'd bet it's the vacuum booster. Confirm this and then replace it ASAP. You do NOT want to be on the road when it fails - I've been there. Had to use the emergency brake so I didn't run over a dozen college students who ignored my panicked horn.

 

[dan2286]

no its actually a little more mushy or soft ,however you wanna describe it, than it should be but its not going all the way to the floor

One other thing to check is to see if any fluid is leaking behind the master cylinder where it bolts up to the booster. They usually only leak very little and you might not notice it. That is the only other thing that I can think of that would cause the hissing noise if there is no other visible leaks.

 

[Blake442]

Inspect your check valve as well. It's that black plastic thing on the hose coming out of the brake booster. It may be cracked.

Having a power booster fail kinda sucks... hope your legs are strong.

 

[xminnis]

I'd bet it's the vacuum booster. Confirm this and then replace it ASAP. You do NOT want to be on the road when it fails - I've been there. Had to use the emergency brake so I didn't run over a dozen college students who ignored my panicked horn.

Im new to all this, how can i check to see if that is the case?