Break hissing sound?

When I hold the break at a stop, it makes a hissing sound. I'm not to framiler with mercurys or breaks, so what could it be? I assume the breaks are presurized, so maybe a leak? Is there a common place for them to leak, kinda sounds like above the pedal but i didnt see anything.


Thanks
Tom

sounds like the brake booster is leaking, does the pedal fell hard when you step on it? the brake booster is the black round canister that the master cylinder mounts to, it has a vaccum line attached to it.

The breaks feel extremly light. If i push down like half an inch, it almost comes to a stop from 45mph. is that normal?

B-R-A-K-E.....brake,like on a car.
B-R-E-A-K.....break,like I'm on a coffee break.

sounds like the brakes are working fine. the brake booster is a vaccum canister, when you step on the brakes the vaccum "assists" the force needed to apply the breaks. the hissing is probably air being sucked in around the plunger that pushes on the vaccum booster. if your pedal gets hard to push to stop then you'll need to replace the booster.