Why Are My Car Brakes Making Noise?

Unusual noise coming from your brakes is a warning that one of your car's most critical safety systems is malfunctioning. Don't ignore it.

Brakes are one of your car’s most essential safety systems. Fortunately, most brake noises are considered normal and do not indicate a problem. But if you notice excessive grinding or squeaking when braking, it’s time to let a trusted mechanic check your vehicle. Constant or strange brake noise can be a sign that your brake hardware simply needs to be lubricated, or it can be a warning that brake system components are wearing out or need servicing.

Types of Brake Noise

Squeaking

Brake squeaking is the most common “bad” brake noise. Modern brakes use a cast-iron disc (rotor) squeezed between two metal-backed brake pads lined with friction material, mounted inside a brake caliper. The friction material generates heat while braking. This heat (friction) of the pads pressing against the rotors slows and stops your car.

Brake pads or rotors that are worn below manufactures specs, glazed or warped cannot dissipate heat. They will overheat and vibrate, causing brakes to squeak.

Under the right conditions, the pads, disc and caliper will vibrate at a specific frequency. The volume of the squeak can change with speed and brake force, but the tone remains constant due to the mass of the rotor.

Some brake pads come with a wear indicator that produces a loud squeal when the friction material is worn down, indicating the pads need replacing.

Rattle

Worn, loose, defective, missing or unlubricated brake mounting hardware — specifically brake anti-rattle clips, caliper slide pins or shims — will cause the brake pads to rattle when pressing or releasing the brake pedal. Worn brake hardware will also cause pads to drag on the rotors, overheat, vibrate and wear faster and unevenly.

Grinding

There are plenty of reasons for grinding brakes. Overnight a light layer of rust can form on a rotor. Once brake pads and rotors heat up, the noise stops.

Loud grinding when stopping usually indicates the brake pad friction material is worn to the point where the pad’s metal backing is digging into and scoring the rotor.

A rotor surface with excess rust or pitting from mud and road salt will cause grinding while stopping. A faulty wheel (hub) bearing can cause excessive rotor runout and vibration. Mechanically coupled to the brake rotor, bearing vibrations transfer to the brake caliper and pads. This can cause the brakes to squeal or grind, or your car to pull to one side when stopping.

Rust or a stone jammed between the rotor and brake backing plate/dust shield will also make a grinding sound while you’re driving or braking.

Brake Fade

Brake fade is a loss of braking power due to overheated pads and rotors unable to generate sufficient friction to slow a vehicle. Overheated brakes squeak and squeal.

Besides the caliper not fully retracting, brake pads and rotors can overheat from getting stuck in stop-and-go traffic on a hot summer day, towing large loads or driving down steep hills.

Heat from the brake pads can transfer to the brake fluid. Moisture from the air trapped in severely overheated brake fluid can boil. Boiling moisture (water) produces air bubbles that compresses in brake fluid when you step on the brake pedal. This is dangerous. Air compressing in brake fluid while trying to stop will make the brake pedal feel spongy and can cause the pedal to drop to the floor, greatly increasing stopping distances. If you feel your car is taking too long to stop, pull over and let the bakes cool down.

Always take your vehicle to the pros if you experience excessive brake fade. Excessive heat can cause brake pad friction material to deteriorate, and rotors to crack or become glazed. Your technician should also test the brake fluid’s moisture level.

Disregarding brake noises can lead to expensive repairs. When it comes to your car’s brakes, don’t delay when you hear something weird. Always better to be safe than sorry.

Robert Lacivita
Bob Lacivita is an award-winning auto technician and career and technical educator and freelance writer who has written about DYI car repairs and vehicle maintenance topics, as well as writing state, federal and organizational foundation grants, and helped design a unique curriculum delivery model that integrates rigorous, relevant academic standards seamlessly into technical/vocational training, for more than 20 years. His work has been featured in Family Handyman, a Reader's Digest book and Classic Bike Rider magazine, among others. Bob and his wife lived through 20 years' worth of DIY home remodeling while parenting two (now grown) boys and now relax by watching their three fabulous granddaughters.