I've searched on the forum and haven't had much luck so here this goes...

I have a hissing, sounds like it coming from under/behind the dash. It stops when I hit a higher speed and when i put the brake pedal down maybe half way. what is this???

Thanks!

 

Leaking brake booster. It's sucking air in thru a bad spot.

 

^this

 

So its the booster, not a hose??

 

There shouldn't be any hoses under the dash in that area. If it were a vacuum problem with the heater, it wouldn't work right. I've ran across leaking boosters a few times and you can hear the problem.