You're cruising toward a column of cars waiting at a stoplight. You apply your brakes and are then 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?
An annoying noise can be one of the first signs that's something's wrong. Like everything else automotive, an annoying noise can be one of the first signs that's something's wrong, or it might mean nothing at all 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.
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.
Brakes do not simply fail—they deteriorate. The most common example 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. 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/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 the 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, sometimes continues. All you get for your trouble is peace of mind that the brakes are functioning more or less normally.
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 only occurs 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. A set of brake pad vibration damper pads could cure the squeal, but there's no guarantee. The vibration damper pads are made of a self-sticking fiber material that sticks to the back of the brake pad backing plate. Some come with a mushroom-shaped button spring in the center. The theory is that the pad and button spring cushion the vibration and create extra clearance to either reduce or completely eliminate the vibration/squeal.
Another solution to the pad vibration problem is a good coating of anti-squeal compound, either in spray or liquid application form. These heat-resistant polymer adhesives go on the back of the pad to cushion it from the caliper pistons. Be sure to only apply it to that part of the back that comes in contact with the piston. If it ends up on the front contact area of the pad or shoe, the stopping function of the component will be reduced. The spray helps the pad retract from the piston and quiets the squeal.
Another option for reducing the vibration is to use a thin coating of a high temperature anti-seize compound applied to the same area indicated for the anti-squeal compound. This is a less effective anti-squeal solution, but it also facilitates easier brake pad changes. Unless you use your vehicle on the track and go through brake pads quickly, stay with the first two solutions.
There's no guarantee with either the vibration damper pad or the anti-squeal compound. Used together, you can be assured the squeal will go away or at least be reduced to a much less-irritating decibel level.