What Causes the Screeching Sound When Braking?
4 Answers
Brake screeching may be caused by variations in the hardness of the brake discs, leading to uneven wear and resulting noise. If the issue is due to hard spots, the simplest method is to drive in reverse at about 5 km/h and apply the brakes several times to eliminate the hard spots. More information about brakes is as follows: 1. The braking performance of a vehicle is ultimately determined by the brake pads, so maintaining the good condition of the brake pads is the most direct maintenance method for the braking system. Both brake pads and brake discs (drums) have a service life and must be replaced when they wear down to a certain extent. 2. If the car noticeably pulls to the left or right when braking, this is due to asynchronous braking of the front wheels, which can easily lead to accidents due to uneven braking force, especially at high speeds. Immediate adjustment at a repair shop is necessary.
My old car has been making a screeching noise when braking recently, which really worries me. When I took it to the repair shop for inspection, the mechanic said that such noise is usually caused by the brake pads wearing down to their limit, causing the metal warning tabs inside to come into contact with the brake disc. He showed me with a flashlight that the brake pads were indeed only about 2-3 millimeters thick. Another possibility is the material of the brake pads—cheaper ones with more metal particles tend to squeal when used with hard brake discs. The noise can also occur after rain because the brake disc surface rusts, but it goes away after a few brake applications. The worst-case scenario would be a warped brake disc or a small stone stuck inside, which needs immediate attention. I later replaced them with a set of ceramic brake pads, and the noise disappeared instantly. Now, I feel much more at ease when driving on mountain roads.
Last time when I went to replace the brake pads, I specifically consulted the technician about the abnormal noise. He said the most common cause of brake squealing is friction surface issues, especially when starting a cold car or lightly braking at low speeds. This could be a normal phenomenon during the break-in period of new brake pads, and the noise should disappear after driving a few hundred kilometers. However, if the squealing persists for several consecutive days, it's necessary to check whether the brake discs have grooves or uneven wear. If obvious steps are worn at the edges of the brake discs, causing improper contact with the brake pads, it will result in squeaking. Another less common possibility is abnormal retraction of the brake caliper, leading to constant slight contact between the brake pads and discs. Since then, I've developed a habit of asking the mechanic to measure the brake disc thickness during every maintenance service, and also to clean the dust inside the brake calipers.
My car also experienced brake squealing issues last year, and after some research, I found that heat dissipation was the key factor. After frequent braking on continuous downhill sections, the brake disc temperature can soar to 500-600 degrees Celsius. If you wash the car immediately or encounter water at this point, thermal expansion and contraction can cause slight deformation of the brake disc. This uneven surface friction then produces a metallic screeching sound. Once at a service area, I touched the wheel hub and it was scalding hot, which made me realize it was caused by insufficient heat dissipation. Now when driving on mountain roads, I’ve gotten into the habit of using engine braking by downshifting to give the braking system a break. Additionally, a tire shop owner taught me to sand the chamfered edges of the brake pads with sandpaper, saying it could reduce resonance noise—tried it, and it actually worked.
