brake pedal air noise

[sunedog]

I hear a subtle hissing noise coming from around the brake pedal on my 99 ML 320. It is louder when you first start the truck, but it continues while you drive. If you put even the slightest pressure on the pedal, it stops. The brakes seem to work as they always have and the pedal is high and firm. Master cylinder going bad?

[Jim W.]

I've had that type of noise on another vehicle and it indicated eventual brake failure. We were lucky it didn't happen when we needed the brakes. Recommend to have it diagnosed.

Jim W.

[sunedog]

Will do. Thanks.