When I hit my brakes do I hear air?
When I hit my brakes do I hear air? Cars can make many noises, and a hissing noise when braking can be among them. But if you hear a hissing sound when pushing down or letting up on the brake pedal, it usually is caused by the brake booster leaking air, which could mean there's a leak in the booster diaphragm, master cylinder gasket, or vacuum hose. What makes a hissing noise when you press the brake? He then took it to a mechanic, and when he picked the car up the guy told him the master cylinder needs replacing....