What Causes a Hissing Sound When Braking?
4 Answers
The reasons for a hissing sound when braking are: 1. Use of low-quality or overly hard brake pads; 2. Presence of sand or foreign objects between the brake pads and brake discs; 3. Severe wear of the brake discs; 4. Brake pad warning. The function of brakes is to reduce speed or bring the vehicle to a stop. The working principle involves converting the kinetic energy of the moving vehicle into heat energy through friction between the brake pads and brake drums, as well as between the tires and the ground, thereby slowing down or stopping the car. The causes of brake failure include: 1. Impurities or poor sealing in the brake master cylinder; 2. Failure of the vacuum booster pump; 3. Contaminated brake fluid; 4. Oil leakage from the brake master cylinder or wheel cylinder; 5. Air leakage from the air reservoir or pipe connections; 6. Severe overloading; 7. Carbonization of the brake drum; 8. Insufficient brake fluid in the brake master cylinder; 9. Wear of the brake master cylinder piston.
I noticed a hissing sound when braking, which is mainly due to an issue with the braking system. The most common cause is worn brake pads or hard spots on them—impurities stuck inside that create friction and produce that noise. I’ve encountered this often in my own car, especially in rainy or dusty conditions. Another possible reason is uneven brake rotors, with surface rust or scratches, which can cause squeaking even with light braking. I recommend checking the thickness of your brake pads—they should have at least 3 millimeters left; otherwise, replace them immediately. Also, try pulling the handbrake when parked to see if the noise disappears—this can help you diagnose the issue initially. Remember, don’t delay fixing such minor problems, as they could damage the brake rotors over time, leading to costlier repairs and increased driving hazards.
I think a hissing sound when braking usually indicates an abnormality in the system. For example, if air gets mixed into the hydraulic system, causing poor brake fluid circulation, the sound may come from the pump or pipelines. Brake pads that are too hard or improperly installed can also create uneven friction, producing such noises. This serves as a safety warning: if the sound persists, braking power might decrease, leading to longer stopping distances, especially when going downhill or during sudden stops, which could easily cause accidents. Therefore, I recommend you drive to a nearby repair shop as soon as possible for inspection to check for air leaks or replace the brake pads with qualified ones. When driving normally, avoid sudden braking and stops to reduce wear and protect the entire braking system.
There are several reasons for the hissing sound during braking. First, the brake pads may be nearly worn out, causing the metal parts to rub against the brake discs, producing a sharp noise. Second, the brake disc surface might be rusty or contaminated with sand or dirt—restarting after parking may reduce the noise. I've encountered this a few times myself and tried simply wiping the brake discs with a damp cloth, which sometimes resolves minor issues. However, be cautious: this sound often indicates reduced braking effectiveness, so don't push through it. It's best to regularly check your vehicle's condition and ensure the brake system is inspected during annual maintenance to guarantee safety.
