Squealing brakes are embarrassing. There is little a driver hates more than those annoyed stares from everyone within earshot after stopping at an intersection. But more than that, brake squeal can be an indication of serious brake problems in the making. Fortunately, by following a systematic troubleshooting approach, you can tackle the root cause of your squealing brakes and bring peace and quiet back into your motoring experience again. Your neighbours will thank you too.
Analyse the brake squeal. Identify whether the squeal comes from one wheel in particular, just the front or back wheels or all of the wheels. Determine if the squeal is audible all the time or only when the brakes are applied. Ascertain if the problem started suddenly and, if so, whether this coincided with a brake servicing. Make a list of everything you can think of regarding when the problem started and how it has progressed.
Be sure new brakes are properly bedded. New brake pads require a few hundred miles of city driving before they are completely worn in with the brake rotor. During this wear-in period a tolerable amount of squeal is normal. You can speed up the bedding process by performing about half dozen rapid slowdowns from highway speed to about 20mph or so and then driving the car without stopping for about 15 minutes to let the brakes cool. The decelerations must be in rapid succession so the brakes do not cool in between.
Install noise-reducing shims on the backs of your brake pads. These will reduce squeal by dampening the pad's high-frequency vibrations. If your pads are newly installed, they may not have come with shims, and even if shims were included, they are perhaps not the best quality. Purchase high-quality noise reducing shims from your local auto parts store and install them. Applying anti-seize compound to the back of the piston face where it contacts the back of the pad will often reduce or eliminate squeal. The compound may have to be reapplied from time to time to keep your brakes quiet.
Check that your brake pads are not worn out. Many pads have a springlike metal leaf wear indicator that will scrape on the rotor when the pad lining wears down to the minimum thickness. This creates a loud metallic squeal to warn the driver that the pads need replacement. This type of wear indicator is typically present on the inside pads only. Replacing worn-out pads will solve this problem.
Examine the brake pad and shoe linings to see if they are damaged or unevenly worn. Uneven lining wear will create uneven pressure against the rotor or drum during braking, sometimes causing a squeal. For disc brakes this is normally caused by a seized caliper, meaning that the caliper slide pins should be thoroughly lubricated and new pads installed. On drum brakes this normally means that the shoe hold-down pins are bent or damaged, in which case new shoes and hold-down pins should be installed.
Check the brake pad design. Some brake pads, such as ceramic pads, have very hard linings, and these are more prone to squeal than softer linings. If your pads are too hard, you can change to a softer pad to see if the squeal goes away. Many high-end car manufacturers use non-asbestos organic fibre pads in order to reduce brake noise. High-quality brake pads often have bevelled leading and trailing edges on the pad lining. By comparison, low quality pad linings usually have sharp corners. Pads with sharp corners are more prone to squeal, especially during the bedding period, and changing to pads with bevelled edges will often fix the problem. Some brake shops and auto parts stores can bevel the lining edges on your existing pads for a reasonable cost.
Inspect the parking brake. If you detect a continuous faint squeal from one or both of the rear wheels while the car is moving, and the sound disappears during braking, it may be caused by a seized emergency brake. Be sure the emergency brake handle or pedal is releasing properly. Check the cable at the rear brakes to be sure it is not still tight even when the emergency brake is disengaged. Check the length of the emergency brake cable for signs of rust or corrosion. Corroded cables should be replaced.