96 GMC Sierra 1500 has hissing noise from brake pedal. Help?

[Josephine]

When I apply the brakes I hear a hissing air sort of noise. It sounds like it's coming from under the dash, or close by, like in the area where the brake pedal is. What could be causing this?

 

[bandit_60]

it,s coming from your brake booster. the booster probably has a hole in it letting the air escape.

 

[pedro7of9]

power brake booster
or master cylinder
1 got brake fluid? check it
2 brakes ok? dont worry...replace only if driving you nuts
3 open hood..get someone to press brakes while looking...listening,,,

 

[Scotty Bad]

My 2002 Oldsmobile does the same thing. GM brake boosters tend to do that. It's nothing to worry about. If the brake pedal starts to feel soft or you notice fluid dripping near the wheels, then you have a problem.

 

[RacingFan]

My '97 Sierra had the same thing

Last week my '97 4WD did the same thing, it was the brake power booster. A friend of mine is a mechanic (lucky me!) so we replaced it this weekend. Not a super complicated job, took about an hour, maybe slightly more.
Good luck with yours!