What are symptoms of a failing brake booster?

A failing brake booster often leads to a hard brake pedal, making it difficult to apply the brakes with the usual amount of force. This occurs because the vacuum assistance that helps amplify the driver's input on the brake pedal is compromised. The hissing noise indicates that air is leaking from the booster, which can be a sign of a damaged or failing diaphragm within the booster.

The combination of a hard pedal and a hissing sound are significant indicators of issues with the brake booster. In functioning systems, brake boosters rely on vacuum pressure to function smoothly, so any disruption in this pressure will be noticeable in brake operation and could lead to safety concerns if not addressed.