You’re cruising toward a column of cars waiting at a stoplight. You apply your brakes and are rewarded with a sound that, like fingernails on a chalkboard, raises goose bumps on your neck – and maybe the blood pressure of the driver in front of you. Sound familiar?
Like everything else automotive, an annoying noise can be one of the first signs that something is wrong, or it might mean nothing is amiss. It’s up to you to quickly figure out which. Keep in mind that in most cases, a persistent noise, even after the brakes have warmed up, indicates that a repair is in order. To help determine whether squealing brakes are simply a nuisance or an ominous sign, here’s a quick run-through of the disc brake action that starts with the foot on the brake pedal and ends with a stopped vehicle.
Car brake action
The pedal pressurizes a hydraulic system that pushes the brake caliper pistons out of the calipers, contacting the brake pads and pressing them against the spinning brake rotors. The contact of the pad’s friction material on the rotors converts kinetic energy into heat and slows the vehicle. The obvious first step in the squeal search is to eliminate serious system problems. Brakes do not simply fail – they deteriorate. One element of the system wears and, over time, takes the rest of the system with it.
Uneven braking pressure causes pads to flex
Brake system wear
The most common example of deterioration is a badly worn brake pad, a simple and inexpensive fix. The next component in line for wear is the brake rotor that the pad rides against when the brakes are applied. A brake pad, worn down to its backing plate, will eat grooves in the rotor, which is not an inexpensive fix. To avoid the domino effect of worn brake parts, check for excessive pad or shoe wear. Look for oil or grease on pads or shoes, warped or scored rotors or drums, misaligned or loose calipers and sloppy wheel bearings. Also be on the watch for glazed pads or rotors or sticky pistons. If there are rust or corrosion deposits on brake elements, this could be a sign that the piston is sticking. If pads or shoes are worn unevenly, side to side, a sticking piston could also be to blame. Even after you and/or your mechanic have determined your brake system is in tip-top shape, the squeal, out of sheer automotive spite, can sometimes continue. All you get for your trouble is peace of mind that the brakes are functioning more or less normally.
Pad Flexing causes Noise Vibration and Harshness
Reducing car brake noise
There are a few options, though, to quiet the noise. If you’ve recently purchased high-performance carbon-metallic brake pads, know that this material is prone to noise. So you may have to either live with the squeal or go back to original equipment pads. If the squeal occurs only when your brakes are hot, that’s normal. If you’re using your brakes to control speed down a steep grade, you may want to let the engine do the work by shifting to a lower gear. As brakes heat up, they become noisy and less effective. If the noise pops up just before your vehicle comes to a complete stop, as opposed to squealing throughout the entire range of braking, the cause could be a brake pad that is vibrating against the rotor.
Increasing the number of brake pistons reduces pad flex