where's the cruise control/brake switch under the dash(possible vaccum leak)
 

My brakes are soft and I hear a hissing sound everytime I depress the brakes. I read theres a switch that could be leaking. I do have or had cruise control. where's the switch to look for?

before going to far, there will be a normal hiss sound when the brake is applied. now, does it continue to hiss one the pedal is held? if so, then it may be that switch. ive never replaced one, so i cant tell you where it is. as for the brakes being soft, flush the fluid, i bet its 15 years overdue

the hiss is pretty long. Thebrakes eventually end up on the floor. they still work though. What isthe valve between the booster and engine.

Well its more of a whistle than hiss. Guys got any ideas?

The switch your looking for is on the upper portion of the pedal arm.You'll have to remove the under dash cover.There is a large vacuum line (bout 1/2 dia) attached.Thats the c.c line.

The valve on the booster line is a one way valve to keep vacuum on the booster diaphram.

Your pedal going to the floor could mean you have air in the brake lines.

...And looks like this. The brake pedal arm pushes in the red button and breaks the vacuum connection.
Remove and plug the vacuum hose from it, then listen for the whistle again.

Attachment 32972

that sounds more like a bad master cylinder and the vacuum diaphragm in the booster is torn. its not that hard or expensive of a job to do on a third gen. cost is about $100, and maybe 2-3 hours

found the switch! Plugged the hose up and the brakes feel better. Bleeding them should do the trick now. I felt like bleeding them before was gonna be a waste of time since I knew there was some kind of vaccum leak somewhere. Hissing/Whistling went away. Thanks Fellas!

No prob. I had that exact same thing happen to me on a 78 Vette I had. Hit the brake pedal and got a bad vacuum hiss. So figuring it was obviously a bad booster, I replaced it. It wasn't the booster, it was the cruise control switch. Learned the hard way, but did put the old booster back in and returned the "unused" new one!