Hearing air sound when pressing brake pedal

[Jesus A Rodriguez]

Just picked up my 04 LS V8 from getting most of the coolant hoses done. Just got home after driving around and as I was parking I heard a air sound when I pressed the brake pedal. What could this be?

 

[Telco]

Sounds to me like a leaking diaphragm inside the brake booster, which is the large round thing on the firewall right in front of the driver. It'll get worse over time and will eventually affect braking ability.

 

[joegr]

A slight hiss in the cabin is normal while the brake pedal is moving. If you are hearing it while holding the brake pedal still, then that is a problem.

 

[Jesus A Rodriguez]

A slight hiss in the cabin is normal while the brake pedal is moving. If you are hearing it while holding the brake pedal still, then that is a problem.

I hear the sound as I'm pressing the brake down.

 

[joegr]

I hear the sound as I'm pressing the brake down.

Depending on the volume, I would say normal. I only notice it if I have have my head down near the pedal, or if everything else is really quiet. The booster works by having engine vacuum on both sides of the diaphragm. When you press the pedal, a valve lets air into the back side until the diaphragm moves forward as much as you have pressed the brake pedal. If you hold the pedal still in any position, the valve closes. It's only really open when you are moving the pedal.