Auto Care Advice: Why Are My Brakes Making Noise?
What's the Noise? How Severe Is the Problem?
Determine under what conditions and from what area of the vehicle you hear noise.
Do you experience the noise only during the first few brake applications in the morning?
Do you hear the noise when braking at higher speeds, or when you gently apply the brake?
Does the noise appear to be a grinding or clunking sound, or a higher pitched squeal?
Does it appear to come from the front or rear of the vehicle?
Noise heard while braking is an indication of brake wear and the brakes should be inspected. Brakes are very much a safety item, and delaying repair is not a safe strategy. In fact, delaying repair can potentially lead to more expensive repairs because worn brake pads can wear down to the metal backing. When the squealing turns into a grinding, the brake rotors are likely being damaged (often requiring replacement).
What's That Squealing? How Do I Know if I Should Get My Brakes Inspected?
Before we assume the brake pads are worn, it’s important to understand that overheating brakes can cause a light squeaking, especially when the brakes are still cold. If there is sufficient pad material remaining, heat is a possible cause for squeaking.
Many car manufacturers incorporate some form of early warning system to alert the driver that the brakes need service. European cars typically use a warning light on the instrument cluster to alert the driver when it's time to replace the brake pads. A sensor deteriorates when the pad is worn to the minimum allowable thickness and then issues a warning light. Sensors are normally replaced when the brake pads are replaced.
Many Asian and American vehicles have a metal "finger" (sensor) that is an integral part of the brake pad. As the pad wears down, the sensor contacts the rotating brake disc (rotor), creating a high pitched squealing sound almost comparable to running your fingers down a chalk board. Brakes should be inspected periodically for wear and replaced as required. You should not rely on the visual or audio warning as your means of assurance that your brakes are okay.
Continually driving a vehicle until the friction lining of the brake pads is worn away will lead to expensive damage—your brakes might even fail. Anytime the brakes make an abnormal noise, they should be inspected and repaired before the braking system becomes compromised in any way.
What Are Brake Pulsations?
Sometimes pulsations can be subtle and only your passengers notice. They might even be annoyed because they think you're tap-tap-tapping the brake pedal. Pulsations can be felt when you hold consistent pressure on the pedal, but the vehicle does not slow down smoothly. Sometimes this can even feel like the brake pedal is pushing back on your foot, almost like you are doing leg presses at the gym!
The surfaces of the brake rotors must be flat and smooth, and both sides of each brake rotor must be parallel to each other (uniform thickness). This minimizes brake noise or brake pedal vibration when the brakes are applied. If the braking surface is not parallel to the wheel mounting surface, the brake rotor is considered to be warped. If the brake rotor is warped and/or no longer parallel, the brake rotor can be machined, provided it is sufficiently thick enough to have material removed. There is a minimum allowed thickness specification for brake rotors. The brake rotors are accurately measured for thickness variation and "run out" to determine if they will be serviceable after they are machined.
What Are My Options?
Brake linings are a maintenance item and are designed to wear. There are three main types of brake pads available for your vehicle. The different friction (stopping) materials—organic, semi-metallic, and ceramic—each have their own characteristics. When it's time to replace your brake pads or shoes, discuss your driving habits and how you use your vehicle with your shop or parts provider. Original equipment brake pads from the dealer are always a good option if you have been satisfied with the braking performance. You won't usually have the same amount of options from a dealer, but you can be sure you will be buying a quality brake pad set.
Brake pads generally have silencing shims fitted to them to dampen vibrations and/or locate the brake pads in the brake caliper. If the silencing shims and other brake hardware are assembled incorrectly, missing, or damaged, you may experience an abnormal noise when the brakes are applied.
A Little Background ...
All modern cars have disc brakes in the front. The brake rotor is like the rim of a bicycle—it rotates with the tire and wheel. When the brakes are applied, the brake pads put clamping pressure on the brake rotor in the same manner the rubber brake blocks come into contact with the rim of a bicycle. The pressure the brake pads apply to the brake rotor is proportional to the pressure applied to the brake pedal by the driver's foot.
Brake pads wear depending on driving habits and vehicle use. Front brake pads typically wear two to three times faster than the rear brake linings. Vehicles equipped with automatic transmissions tend to wear brakes out quicker than vehicles with manual transmissions.