Ford Expedition hissing noise when braking due to brake booster and cylinder issues, affecting gas mileage and braking performance on Ford Expedition

Some Ford Expedition owners report experiencing a hissing noise while braking, which is often linked to problems with the brake booster and cylinder. This hissing noise is commonly associated with a leaking brake booster, potentially impacting the vehicle's braking performance. Owners note that the noise typically occurs under moderate pressure on the brake pedal and may change or stop when the pedal is fully pressed. Additionally, a leaking brake booster can release air, affecting the braking system's efficiency and possibly decreasing gas mileage. In some instances, the hissing may result from a failed check valve on the booster where the vacuum hose connects. Furthermore, issues with the brake cylinder, such as leaks or malfunctions, can also contribute to this noise and compromise overall braking performance. It is crucial for owners to address these brake-related issues promptly by having the brake booster and cylinder inspected and repaired by a qualified mechanic to ensure safety and optimal vehicle function.