What Causes the Squeaking Sound in BMW 3 Series Brakes?
4 Answers
The reasons for brake squeaking in BMW 3 Series are as follows: 1. Use of inferior or overly hard brake pads: If inferior or overly hard brake pads are used, they will produce a squeaking sound when rubbing against the brake discs during braking. Therefore, it is essential to use high-quality brake pads when replacing them. 2. Presence of sand or foreign objects between the brake pads and discs: During normal driving, it is inevitable to encounter complex road conditions. Due to the unique design of disc brakes, some sand or foreign objects may get between the brake pads and discs, causing abnormal noises during braking. 3. Severe wear of brake discs: For new cars, a slight squeaking sound during braking is normal and should diminish with more driving. For older vehicles, the noise might be due to rust on the brake discs or pads, which can be resolved by removing them and sanding off the rust layer. If the brake pads are severely worn, they should be replaced. 4. Brake pad warning: There is no strict mileage requirement for replacing brake pads; they should be replaced once they become thin. Some brake pads come with electronic warnings, while lower-end vehicles use warning clips. When the wear reaches the warning line, a squeaking sound will occur, indicating the need for immediate replacement. 5. Incorrect installation of brake pads: If the brake pads are installed incorrectly or do not match the model, abnormal noises may occur. In such cases, the brake pads should be reinstalled. It is advisable to have brake pads installed at professional auto repair shops, especially for owners who have had them replaced at roadside stalls, as extra caution is needed.
To be honest, friends who drive BMW 3 Series often ask me about the squeaky brake issue. This situation is most likely caused by brake pads. The OEM brake pads are made of harder materials, which are wear-resistant but prone to producing sharp noises when cold or at low speeds. Also, if the brake disc surface is scratched by hard objects like small stones, or if the disc surface is uneven with grooves, the metal scraping sound between the pads and disc can be quite annoying. Newly replaced pads will have a break-in period, and the noise will naturally disappear after driving 200-300 kilometers. However, if you feel steering wheel vibration during braking, you should immediately check for brake disc warping—this is no small matter.
When repairing cars, I often encounter BMW owners complaining about brake noise. Apart from common issues like hard brake pad material or surface impurities, there's a detail that's often overlooked: the anti-rust coating on brake discs not being completely worn off during the rainy season can also cause squeaking. Some cars have weakened damping shims on the back of the brake pads, causing a metallic clinking sound like coins hitting the ground when going over speed bumps. Also, if the caliper guide pins lack lubricant and retract slowly, continuous hissing occurs in a dragging state—then you should be alarmed if the wheel hub feels noticeably hot to the touch. It's recommended to focus on identifying the sound location when starting the car cold, as diagnosis is most accurate at that time.
Last time my wife's BMW had this issue - the rear wheels would make a metallic scraping sound after hard braking. We took it to our regular repair shop, where the mechanic disassembled the rear wheels and found a dried leaf stuck in the dust cover. BMW's ventilated disc design is prone to trapping foreign objects, especially after washing the wheels with high-pressure water jets. Further inspection revealed the caliper guide pins had dried and hardened grease, preventing the brake pads from fully retracting and causing constant friction against the rotors. It's particularly noticeable in cold weather - squeaking like mice chirping during morning starts. The mechanic warned that leaving this untreated would cause abnormal wear and grooves on the brake discs.
