Skip to main content

Why do my brakes squeal?

  • Story Highlights
  • Brakes can squeal because of worn pads, glazed pads and rotors
  • Also, broken anti rattle clips, lack of pad insulation or insulation shims
  • When pads are replaced, shims must be replaced or silicone insulation gel applied
  • Rotors must be resurfaced to remove glazing, return the surface to "true"
By Tom Torbjornsen
Decrease font Decrease font
Enlarge font Enlarge font
New Cars, Used Cars, Kelley Blue Book Values at AOL Autos

(AOL Autos) -- Automotive expert Tom Torbjornsen answers a woman's question about squealing brakes.

Dear Tom,

Every time I hit the brake pedal, my brakes make this awful high-pitched squeal. When I stop at a light I get stares from people. It's embarrassing! I just had the brakes done last month, so why are they squealing? Help!
Melissa from Manhasset, New York

Hi Melissa,

Take your car back to the shop. Sounds to me like the pad insulators, anti rattle clips, or calipers are loose. The squeal you hear is the result of vibration of the brake pads. I would not expect to be charged; this should be covered under the brake job warranty. -- Tom

Melissa brings up a popular topic that needs to be addressed. Brake squeal is common and can be caused by a number of conditions: Worn pads, glazed pads and rotors, broken anti rattle clips, lack of pad insulation or insulation shims, and incorrect rotor surface cut or no surface cut at all. Let's take a closer look.

Worn pads

A brake pad is comprised of steel backing with friction material attached to it. Application of the brakes produces hydraulic pressure that causes the brake pads (via brake calipers) to clamp down on the rotors (discs) creating friction. It is the friction of the pads against the rotors that slows and stops the vehicle. When the friction material on the pads wears down, it is time to change the pads.

Some pads are equipped with a wear indicator, which is a small spring steel clip. When a pad is worn, this clip makes contact with the rotor and generates a high-pitched squeal, telling you that it is time to service the brakes. If the pad does not have a wear indicator, then when the pad has worn down to the steel backing it will grind into the rotor and need to be replaced.

In this scenario, the rotor may have to be replaced as well, depending on how badly it was affected. AOL Autos: Common signs of brake failure

Glazed pads and rotors

Brake squeal can also occur when brake calipers stick and the brake stays partially applied. When this happens the pad is in constant contact with the rotor, producing excessive friction and thus heat. Overheated pads harden and crystallize.

This glazing occurs on the rotors as well. The squealing sound is a result of these super hardened surfaces coming in contact with one another. Remember, it is the friction created by the brake pad against the rotor that stops a vehicle.

When crystallization of pad and rotor occurs, there is much less friction. This results in diminished braking power and squealing brakes. At this point the pads must be replaced and the rotors resurfaced or replaced. AOL Autos: Are extended warranties worth it?

Broken anti-rattle clips

The brake pad is loosely held in place on the caliper by pad stays. An additional part called an anti rattle clip is used to secure the pad so that it will not vibrate or rattle when the brake is applied. If anti rattle clips are worn or broken, pad vibration will cause squealing. In this case, the clips must be replaced. AOL Autos: Maintenance is the key

Lack of pad insulation or insulation shims

When a car comes from the factory, insulation shims are placed against the steel backing of the pad to insulate it from the brake caliper. This is necessary to prevent brake squeal. These shims eventually wear out or they are discarded when a brake job is performed.

When the pads are replaced, either the shims must be replaced or silicone insulation gel must be applied to prevent squeal. If you had your front brakes replaced recently and they're squealing, take it back to the shop and make sure the shims were installed or gel was used. AOL Autos: Eight great auto questions

Incorrect rotor surface cut or no surface cut at all

When a brake job is performed, the rotors must be resurfaced to remove any glazing and return the surface to "true." First the rotor is machined to remove grooves and/or imperfection on the rotor surface. Once the rotor face is "true," a slow, non-directional finish is applied to the rotor face to ensure proper break-in of the pads.

This process also insures that the pads don't ride up on the face of the rotor when braking. Riding up of the pads can cause a clicking noise, the breaking of anti rattle clips, or caliper pin wear.

If the rotor is found to be too thin according to state inspection rules, it is discarded and replaced. It is important to note that if your pads were replaced without resurfacing the rotors, then squealing and pedal pulsation will probably occur. AOL Autos: Inspect your car for rust and winter damage

© 2009 AOL, LLC. All Rights Reserved.
  • E-mail
  • Save
  • Print