Brake System Issues (Page 3/3) Mike in Sydney JAN 13, 04:51 PM quote Originally posted by WaterInYuhDish: With the car OFF, and a few pumps, the brake pedal stiffens. When the car is RUNNING, I hear a hiss and the pedal can be pushed straight to the floor with ease indefinitely. . Does the pedal go all the way to the floor or just close to the floor? Also, do you know if the brakes are actually holding when the pedal is pushed? Try putting the car on jack stands and taking off the off the wheels. Can you turn the brake rotors when the pedal is pushed with the car running? theogre JAN 13, 05:06 PM Booster/vacuum problems Will Not cause a low/floored pedal. Air sound when pushing a low/floored pedal is Normal. Sound is a lot of air moving thru the control valve to help you pushing the pedal. Can even try to stall the engine because act as a big vac leak during flooring the pedal. Sound will stop only when MC has enough pressure to push back on the booster output pin. Sound may not stop when you have hydraulic problems because the booster can go "out of range" and control valve gets confused trying to floor the pedal. In normal braking, the sound is often still there but less air used means less noise you hear. Many vac boosters have things to reduce normal noise or other design features so can't hear air noise in most settings. Don't crush big vac hoses to test. Can wreck old ones like that. disconnect the hose and plug the open end. Just make sure the plug is made so can't get sucked down the hose/pipe. W/o vacuum the booster will fight you pushing the pedal.