What Causes the Squealing Noise When Lightly Braking at Low Speed?
3 Answers
Low-speed braking squealing may be caused by sand or other foreign objects between the brake pads and brake discs, or excessive wear of the brake pads, leading to the exposure of friction material fixing points that rub against the brake discs or brake calipers, producing abnormal noises. Below are the relevant explanations: Replacing Brake Pads: First, check whether the brake pads are nearly worn out (indicated by the wear indicator). If the brake pads are worn out, a new set of brake pads needs to be installed. Typically, brake pads have a wear indicator pin that contacts the brake disc when the pad wears down to a certain level, causing a metal-on-metal squealing noise. If the pads are new, check for any foreign objects trapped between the brake disc and pad. Inspection and Repair: If the abnormal noise is accompanied by brake system failure, inspection and repair are necessary. Missing or damaged brake disc mounting screws or insufficient lubrication can also cause brake noise. Abnormal wear on the brake disc may result from a dirty disc surface, uneven material density, excessively high operating temperatures, or mismatched installation torque. If the brake disc has deep grooves due to wear, it must be replaced with a new one.
I had the same issue when driving our family's old car last time - a screeching sound when lightly braking at low speeds, which was quite scary. This is usually caused by brake pads being too hard or excessively worn, and sometimes uneven brake rotor surfaces can also cause friction noises. Especially on rainy days or in humid conditions, brake pads are prone to rust, making that piercing sound even more noticeable. Later, I took it to the repair shop for inspection. The mechanic said the metal particles in the brake pads were unevenly distributed, causing friction that sounded like nails on a chalkboard, and recommended I immediately replace them with a set of softer brake pads. After the replacement, it became much quieter, and I never heard the screeching again. I suggest you promptly check the thickness of your brake pads and the flatness of your brake rotors. Spending a little money to fix the problem is much better than risking an accident.
This low-speed brake squealing issue is actually quite common. I've encountered it many times while repairing cars. The most frequent cause is foreign objects between the brake disc and pads, like small stones or dust stuck in the gap that squeak when rubbing. Another possibility is the anti-noise shim of the brake pad falling off, or the guide pins of the brake caliper lacking lubrication and getting stuck. I remember once when helping a friend check, we found the backing plate spring of his brake pads was loose, causing vibration and noise with just light braking. Also, if it's a new car, it might just need a few hundred kilometers of driving for the brake pads to properly break in. I'd suggest trying several hard brakes at medium speed in an open area - sometimes the heat can burn off any debris. If that doesn't work, it's best to remove the wheel to clean the brake components or apply some anti-squeal paste.
