BN7877

Hi y'all!

Well today i finally got my hands on a white 2007 GT/CS from a mom n' pop dealership. Of course it has its "details" but there's this one thing that has been bugging me and I can't seem to figure out what it is.

So everytime the car is started and running, there is this steady hissing sound by the brake booster. It seems like its right there where the hose connects to the booster itself. Right when I disconnect the hose from the booster, it still hisses for another second then softly disappears.

Also, while in the car I hear a hissing sound near the break pedal. When I press on it, the sound mutes a bit lower until I let go of the pedal. The brake pedal itself is rather quite firm and wont let me push the pedal all the way to the back quickly.

is it something simple as a hose or a gasket or are we talking something much serious?

Thanks in advance!
- Fern

08'MustangDude

The fitting for the brake booster is solid plastic, and it's a check valve. It can
be leaking somewhere, small hole, or past the seal where it goes into the booster.
You would need to replace it, with a new check valve, or the seal. This will be
your hard pedal, if the check valve has failed.

If continually hissing is IN the car, at the brake pedal, then the diaphragm is bad, you need a
booster. This can also cause a hard pedal, as the vacuum leaks past the diaphragm as
you brake.

BN7877

The hissing sound is the same when I pull the hose off the brake booster to the check valve must be faulty.

Also, the hissing under the Dash isnt the exact same sound as the one in the engine bay but it does sound right around where the pedal bolts to the firewall.

But for this case, i would need to replace the booster and not the brake fluid resevoir area, right?