Even when working normally the brakes on your car can make grinding, squeaking, and squealing noises. All brakes work by pressing a high friction material into a spinning metal surface, and vibrations and irregularities cause them to make noises. In normal use, the noise should not be constant and unbearable, but sometimes things go wrong.
Here are some of the common noises brakes make, why they make them, and how to fix them.
Rust or Corrosion
Brake discs (and the friction surface of drums) are raw unfinished iron which means they will rust easily. If you notice your brakes making noises when you first pull away from a parking spot after your car has sat overnight, this is the likely cause. In spring and fall, this can be particularly dramatic, as the warm days and cool nights typically mean moisture that can help rust.
The Fix: This will usually fix itself within the first few brake applications. The only real way to prevent it is to park your car in a warm dry garage overnight. If your vehicle has years of disuse, you should get the discs or drums turned down to remove the layer of rust before putting it back on the road.
Brake Pad Wear Indicators
Nearly all modern cars use disc brake pads with metal tabs to alert you when you have used up 75% of their life. When the brake pad material is worn down, the metal tabs start to drag on the metal discs. If your brakes start to squeak or squeal after 30-60,000 miles of perfectly normal use, this is the most likely cause. Your braking performance is unaffected, and the tabs won’t cause any permanent damage to the discs.
The Fix: The only way to fix this noise is with a new set of brake pads. Replacing the rotors, or resurfacing them, is also a good idea when installing new pads. To confirm the wear tabs are the issue, take off the wheels and inspect the brake pads for wear. These simple, mechanical, warning tabs are a brilliant idea and it is amazing that it took so long for the automotive industry to adopt them.
Glazed Brakes
Do you do a lot of stop-and-go driving? If you live in the typical metropolitan area, of course you do. Applying your brakes lightly, over and over again, as is typical in bumper to bumper traffic can polish discs to a mirror-like surface and glaze the pads. When the pads glaze over it is a microscopic change to the friction material on the very surface of the pad caused by heat.
The Fix: The best fix for this one is to change your behavior and not ride the brake in stop and go traffic. Typically, brakes glazed like this will fix themselves with 2 or 3 hard stops from highway speeds. To avoid it happening in the future, use the brakes with more authority, and avoid repeated light application of the brake pedal.
The Real Squeal
If those first three don’t describe how and why your brakes are making noise, then you have actual brake squeal. This noise comes from vibrations of the disc, caliper and brake pads hitting the resonance frequency of the parts involved. Brakes make noise, but it is generally not an issue until parts start to ring like a bell (and in an audible frequency). This type of squeal is persistent, and the sound tends to stay the same no matter what speed the car is traveling at because the frequency is determined by the parts, not the speed they are moving.
The Fix: The first step to solving squealing brakes is to take apart the pads and calipers, and make sure everything is moving freely. A binding or seized brake can cause this type of noise so check the piston, slide pins, and be sure the pad moves freely. If may help to grease the edges of the pad backing plate or even file them smooth so it moves easier.
On some cars, and with some aftermarket pads, there are thin shims behind the pads that will lessen the noise. These pads work as tiny shock absorbers, keeping the vibration from being passed from the pad to the rest of the car. If your car doesn’t have them, or if they have gone missing, adding them may help.
Some pads squeal on certain models, but not other applications, because of the size and resonance frequency of the parts. One way to change the frequency is to stick the pad to the caliper more securely, so it has to vibrate as a whole. There are any number of pastes available to do this. They are used by cleaning the parts, then applying it to the pad backing plate so the pad sticks to the caliper piston, and on the other side, the caliper itself. Now the whole caliper must vibrate as a whole, and at a different, lower, frequency than before.
If none of these fixes seem to work, it may just be a matter of using a different brand of pad or just a different formulation from the same brand, designed to be quieter.
