I have the exact same problem as this guy...http://www.stangnet.com/mustang-forums/threads/hissing-sound-coming-from-brake-pedal.733836/
I checked the vacuum line at the switch on the brake pedal; everything looks intact and not broken.
Under the hood, I disconnected the vacuum line from the brake booster and plugged the line. Started the car, and no hissing at all. To me that seems to point to a bad brake booster.
Could is be as simple as the check valve on the front of the brake booster (the valve that the vacuum line attaches to)? I'll replace the brake booster if that's what it takes but I'd rather not. I'm getting ready to drive the car from FL to CO in a few weeks so I have to make sure it's as reliable as can be.
I checked the vacuum line at the switch on the brake pedal; everything looks intact and not broken.
Under the hood, I disconnected the vacuum line from the brake booster and plugged the line. Started the car, and no hissing at all. To me that seems to point to a bad brake booster.
Could is be as simple as the check valve on the front of the brake booster (the valve that the vacuum line attaches to)? I'll replace the brake booster if that's what it takes but I'd rather not. I'm getting ready to drive the car from FL to CO in a few weeks so I have to make sure it's as reliable as can be.