I have an 85 F-250 HD, with the dual diaphragm booster and twin piston calipers. I was wondering, when I apply the brakes, I hear a hiss like it is leaking up until the pedal stops, then the hissing stops too. Is is possible, one of the 2 diaphragms is leaking? The brakes work good, like I said, it doesn't hiss while I am holding the brake pedal down, just while the pedal is moving. Maybe it's normal to hear some hissing and I just need to turn the radio up?

 

Almost all vacuum boosters make a "shhh" type of sound as the pedal is pushed. This is atmosphereic pressure entering the booster to provide the assist. Is yours very different from other vehicles?

 

Well my mustang has manual brakes so I can't compare there, and I always have the stereo up in my wifes car, but the truck is still kind of new too me, so I am probably being a little paranoid.

 

Yes and no. A small tear in the diaphram or a leaky air valve will hiss when the pedal is being applied. A loud his is usually a larger tear.

Harold at the power brake x-change can either rebuild 4 you or sells parts if needed. 1-800-580-5729

WOW real live manual brakes. Takes me back when you would not even go for power steering because it was another pully draining horespower. Got any pics of the stang.

 

Stops pretty good for manual drums, should go with some discs, just haven't found the time or money. Here is a link to my stang.

http://www.cardomain.com/memberpage/344204

Haven't updated in a while, but not much has changed yet.