Rick's Free Auto Repair Advice

Brake noise — grinding or squealing

Brakes make grinding noise or squealing noise

What causes brakes grinding noise and how to fix it

Brake noise is a common complaint. Brake grinding or squealing can be caused by vibration between the brake pad backing plate and the brake caliper or abutment areas or between the brake pad face and the rotor.

The brake noise can be caused by brake pads or brake rotors that are worn, the friction material that has separated from the brake pad backing plate, corroded brake pad backing plate that’s causing the pads to bind in the caliper, rusted anti-rattle hardware or corroded noise reduction shims. If can even be caused by seized caliper slide pins that won’t let the caliper apply or release evenly.

This article is one in a series. If you’d like more information on brakes, click on the following links:

How much should a brake job cost?

What’s the difference between economy and premium rotors?

Why do brakes pulsate? How to prevent pulsation?

What brake pads should you buy? Ceramic or semi-metallic?

Brakes make grinding noise when braking

Worn brake pads cause grinding noise during braking

The most common cause of grinding noise when braking is worn out brake pads that result in metal to metal contact between the brake pad backing plate and the rotor face. In other words, you’ve used up all the brake pad friction material and you’re now destroying the rotors.

Here’s what that looks like

brake pad wear

Brake pad worn off completely down to backing plate causing metal to metal contact

Seized brake pads cause grinding noise while braking

Brake pads must be free to move. If they bind and stay in contact with the rotor face, they overheat and the friction material “glazes over,” causing excessive vibration the next time they’re applied causing the brakes to make a grinding noise when braking.

Rotor grooves make a brake squealing noise

Over time, the rotors and drums can develop grooves and the brake pads ride in the grooves, generating a high pitched squeal, much like a stylus on an LP record. Another possible cause for brake squeal is worn brake pads that are equipped with a wear sensor. The sensor comes into contact with the rotor when the friction material wears down to about 3mm. The wear sensor then scrapes along the rotor making a high pitched squealing noise.

Brake pad noise reduction shim

Brake pad noise reduction shim

Failed noise reduction shims cause brake squeal

Most brake pads require a noise reduction shim to prevent vibration transmission from the brake pad backing plate to the caliper. However, the quality of the noise reduction shim is directly related to the quality level of the brake pad. Install cheap pads and you get cheap shims.

Noise reduction shims look like a stamped piece of soft metal and that’s all the cheap ones are. But the better shims are a multi-layer design with a rubber membrane sandwiched between metal layers. For more information on brake shim construction, see this post.

As noise reduction shims deteriorate they transmit more noise. The shims are supposed to be replaced during a brake job. But some shops and most DIYers try to cut corners and reuse old shims. That’s a really bad idea. The same thing applies to abutment hardware anti-rattle clips. These stainless steel clips are designed to maintain just enough pressure on the brake pad backing plate to prevent vibration while allowing the pad to slide so it can apply and release. As the abutment hardware is heated by brake application and ages, it loses spring tension. That allows the brake pad backing plate to vibrate. In addition, abutment hardware can rust and prevent the brake pad from retracting, causing it to remain in contact with the rotor for prolonged periods. Both conditions cause the brakes to squeal.

To correct the situation, replace the noise reduction shims and abutment hardware. Clean the abutment areas shown in these photos. Then apply a light coating of high-temperature synthetic brake grease to the brake pad backing plate ears and abutment hardware. The brake grease lubricates and cushions the vibration.

On drum brakes, make sure there’s adequate friction material remaining on the shoe web. Then clean and lubricate the three pivot points for each shoe. Make sure the automatic adjuster is free of rust and turns freely. Install new retraction and hold-down springs. Then adjust the shoes.

Anti-rattle clips

abutment hardware, brake hardware, pad slide

Abutment hardware – new versus old and rusted

Anti-rattle clips also reduce vibration transmission. During a new brake job, the technician applies a light film of high-temperature synthetic brake grease to the slide areas on the clips. That helps the brake pad “ear” move slightly with each brake application.

However, anti -rattle clips lose their tension over time and rust. Once that happens, the conduct normal brake vibration directly from the brake pad backing plate to the caliper. That causes squeal.

What causes brake pad binding?

caliper pin

Corroded caliper slide pin can cause caliper to bind

However, unlike the high pitched squeal noise, grinding noise is often caused by a binding condition.

Floating brake calipers must move freely on the caliper slide pins. Even a small amount of slide pin corrosion can prevent the caliper from releasing properly. That keeps pressure on the brake pads, causing them to vibrate overheat and create a grinding sound.

To diagnose a grinding condition, compress the caliper piston

caliper slide bolt, caliper pins, slide pin, caliper hardware

New caliper pins

slightly, remove the caliper and check the slide pins for ease of movement. If they don’t slide freely, try applying a high-temperature synthetic brake grease. If they still don’t slide freely, replace the pins or bracket. Depending on the condition of the brake pads, you may need to replace them. And, if the rotor is heavily scored, replace it. To break rotor glaze, some shops use a random orbital sander with 120-grit sandpaper to apply a non-directional finish to the rotor. If you have a random orbital sander, you can try this approach. If that’s not enough to return the rotor to a non-grinding condition, replace the pads and rotors as a set.

©, 2013 Rick Muscoplat

Posted on by Rick Muscoplat

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