What Causes the Sound of Grinding Brake Discs When the Car Moves?
3 Answers
When the car starts, the sound of grinding brake discs is caused by the friction material in the brake pads being too hard. Below is an introduction to brake pads: Concept: A brake disc, simply put, is a round disc that rotates when the car moves. The brake caliper clamps the brake disc to generate braking force. When the brakes are applied, the caliper clamps the brake disc to slow down or stop the car. Brake discs provide effective braking and are easier to maintain compared to drum brakes. Function: Brake pads definitely serve a braking function, with their braking force coming from the brake caliper. Generally, the brake caliper fixes the part where the inner brake piston pump is located, while the outer part is a clamp-like structure. The inner brake pad is fixed on the piston pump, and the outer brake pad is fixed on the outer part of the caliper. The piston is pushed by the pressure from the brake fluid line, moving the inner brake pad, while the reaction force pulls the caliper, causing the outer brake pad to move inward. Both pads press against the brake disc, generating braking force through friction between the disc and the inner and outer pads. In this process, the piston is pushed by brake fluid, also known as hydraulic oil, which is used to assist the engine. For the handbrake, a cable is used through a lever mechanism to forcibly pull the brake pads, pressing them against the brake disc to generate braking force.
Last time I drove, I heard this squeaking noise whenever I moved. At first, I thought it was just the rough road, but the sound became more and more obvious. Most likely, the brake pads were worn to the limit, and the metal backing plate was directly scraping against the rotor. Or maybe a small stone got stuck between the pad and the rotor, causing friction when moving. I drove to the shop for an inspection, and the mechanic took off the wheel to find the pads completely worn out, with deep scratches on the rotor. A new set of pads and rotors was needed. This kind of issue can’t be delayed, otherwise the longer you drive, the more damage it does to the rotor, making repairs more expensive. It’s recommended to check the brake pad thickness immediately—replace them if they’re thin. Always pay attention to changes in noise to avoid worsening the problem.
When the car moves with a grinding noise, the main reason is that the metal part of the brake pads contacts the brake disc due to excessive wear, producing a harsh sound. Another possibility is the accumulation of dust or embedded foreign objects in the braking area, causing abnormal friction. This situation can accelerate component damage and affect braking performance, so it needs to be addressed promptly. I usually perform a preliminary check myself; if the pad thickness is less than 3mm when the wheel is removed, I replace the pads to avoid delays that could lead to higher repair costs. If the noise persists, it's best to consult a professional platform or visit a shop for diagnosis to ensure safe driving.
