What Are the Reasons for Abnormal Noise When Braking?

[VivienneRose]

The reasons for abnormal noise when braking are: 1. Normal activation of ABS; 2. Newly replaced brake pads; 3. Excessive wear of brake discs and brake pads; 4. Sand or mud entering the brake pads. The function of brakes is to reduce speed or bring the vehicle to a stop. Their 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 reasons for brake failure are: 1. Impurities or poor sealing in the brake master cylinder; 2. Failure of the vacuum booster pump; 3. Contaminated brake fluid; 4. Leakage in the brake master cylinder or wheel cylinder; 5. Air leakage in the air reservoir or pipeline 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.

[MacOlivia]

Last week I just dealt with a similar issue where the owner complained about annoying squeaky brakes. The most common cause is worn brake pads, where the built-in warning metal piece starts rubbing against the brake disc, essentially reminding you it's time for new pads. Another scenario is small stones getting stuck in the brake disc, producing a particularly harsh metal-on-metal sound—just park safely and remove the stone yourself. Hard brake pad materials can also cause noise, especially during cold winter mornings, sounding like a whistle. If the brake disc is warped, it'll produce a clunking sound when braking, requiring a trip to the shop for resurfacing. I remember last time encountering rust on discs and pads after being soaked in water, making a screeching noise with every brake application—driving a few kilometers to wear off the rust usually quiets it down. In short, don't ignore unusual noises; check promptly whether it's the warning indicator or foreign debris, as compromised braking distance is the real danger.

[EdenRose]

My neighbor Old Zhang asked me about this just yesterday. His eight-year-old car keeps making a sharp screeching sound when reversing. The key is to determine whether the noise is continuous or only occurs when pressing the brake pedal: continuous noise might be caused by the dust shield rubbing against the brake disc, requiring an adjustment of its position; if it squeaks the moment you brake, it’s likely due to insufficient lubrication on the brake caliper slide pins, causing uneven piston movement. Uneven friction layers between the brake pads and disc can also create high-frequency noise when hard spots make contact. For rear drum brakes, if the return spring is loose and the shoes don’t retract properly, it can produce a knocking sound. Aftermarket brake pads should be chosen carefully—overly hard materials may not pair well with the disc, leading to squealing. I recommend first identifying the source of the noise (front or rear wheels) before deciding whether to remove the wheels for inspection.

[LaSavannah]

Don't panic if you hear brake squealing. Last time my car had this issue after being rained on for two days. Humid weather easily causes brake rotors to rust, and stepping on the pedal produces an annoying screeching sound—just press the brakes a few more times to wear off the rust layer. If you've just installed new brake pads, some noise during the break-in period (within a few hundred kilometers) is normal. It's also common for small stones to get stuck in the brake system; when they scrape between the rotor and pads, it sounds like nails on a chalkboard. Oh, and if the caliper bracket is loose, it makes a clanking noise like a screw rattling in a tin can. For older cars, watch out for worn brake rotor edges—raised lips can rub against the pad edges. A tip: rinse the brake rotors when washing your car, especially after driving on muddy or sandy roads, to clear debris and avoid unnecessary noise.