What does a pssss sound mean when you step on the brakes?

[IronWing]

I have an 1988 Olds Custom Cruiser that has been sitting for about four months. This afternoon when I started it up and took it for a spin I noticed that when I step on the brake there is a pssss noise like an air leak that lasts for less than a second when I depress the brake pedal. It doesn't start immediately but only after the pedal is depressed past a particular point. If I try to hover the pedal over that spot, it doesn't continue to make the noise. Also, if I depress the brake pedal very slowly, it doesn't make the noise as the pedal moves past the spot. The brakes seem to work fine. Any ideas?

 

[exdeath]

Vacuum booster.

 

[IronWing]

Vacuum booster as in expensive or hard to fix part just died or vacuum booster as in there is a rotten $2 vacuum hose somewhere that needs replacing? This car has more vacuum hoses than an ATOT orgy.

 

[LTC8K6]

It's a vacuum leak. Find it. Fix it.

 

[exdeath]

Vacuum booster as in expensive or hard to fix part just died or vacuum booster as in there is a rotten $2 vacuum hose somewhere that needs replacing? This car has more vacuum hoses than an ATOT orgy.

Could be either. But it start with anything connected with the brake booster since you are hearing the sound strongly when applying the brakes.

 

[brblx]

a slight hiss can be normal. it's atmospheric pressure rushing into the booster.

a loud hiss usually means a torn diaphragm inside the brake booster.

it's not a hard part to replace. on older cars, sometimes you don't even have to remove the brake lines from the master cyl- just let it hang there while you change out the booster.