Disc Brake Squeals

by Austin Davis

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Reader Question: I just had my disc brakes replaced and they are now squealing. My mechanic says this is "normal." Why did I have to pay for a "normal" squeal in my disc brakes? Is he just blowing me off?

Dear concerned car owner,

This unfortunately happens more than we like. A certain amount of high-pitched noise from disc brakes is considered "normal" these days because of the harder semi-metallic brake pads that are used on cars now. In my experience, the smaller cars like Honda and Toyota seem to have the most trouble with this. Squeals heard the first few stops in the morning when the brakes are cold and somewhat damp from dew, and squeals that are heard the last few feet while coming to a stop are usually nothing to worry about.

Semi-metallic disc brakes are made of bits of metal shavings in place of the asbestos material that has been banned by the U.S. government. These semi-metallic brakes have great stopping power and have a long wear life, but can cause a high-pitched squeal that drives car owners crazy and frustrates mechanics who can't get it to go away to please their customers.

When are brake squeals not a problem?

Some brands of semi-metallic pads are inherently noisier than others because of the ingredients used in the manufacture of the friction material. Think of it this way, the longer life pads or pads that claim to have more stopping power usually contain more metallic material. Yes, they will last longer and could enhance braking, but the chance of causing a squeal noise is very high. The squealing noise that might be caused from use of these pads does not affect braking performance and does not indicate a brake problem.

Squeal from disc brakes is caused by vibration between the brake pads, brake rotors, and brake calipers. Having the brake rotors refinished or trued (machining a small layer of the metal away from the brake rotor to make it smooth and "true" again) and having a thin layer of a silicone compound placed on the back of the brake pads and on the mounting bolts on the brake calipers are great ways to reduce the squeal if the semi-metallic pads are the culprit of the noise and not due to a worn out brake pad.

Why does this squeal happen anyway?

The brake rotor is the round metal object that the pads on disc brakes squeeze together like the white part of an Oreo cookie. The rotor is metal and has a smooth slick finish, and the brake pads are made of metal shavings and also have a smooth somewhat slick finish. The more metallic material found in the pad the greater the chance for noise, and vise-versa.

The other type of brake pad is called organic. There is no metallic material used in this kind of brake pad. Organic style disc brakes can only be used on vehicles that are specifically designed to use them. Improper use of organic pads on a vehicle designed to use semi-metallic can severely reduce stopping ability. Organic pads are softer than semi metallic and usually do not have a squeal problem. Unfortunately due to shorter life expectancy, inability to stop larger vehicles, and the addition of substances like asbestos in their construction, they are not very widely used.

When are squeals signaling a problem?

Sometimes brake squeals are an indication that maintenance is required. Some common conditions that cause brake noise are:

  • Heat cracked or worn "un-true" rotors
  • Rough finish on resurfaced rotors
  • Loose fitting brake pads in the brake calipers
  • Lack of silicone compound on back of brake pad
  • Missing springs or anti-rattle clips that should be on the brake caliper or pad
  • Improper tightening sequence of lug nuts or caliper hardware

Most GM cars are equipped with a small thin piece of metal attached to the brake pad to act as a warning indicator when the pad material is getting low and the brake pads should be replaced. This inexpensive warning device can be deceiving though, because this warning noise is present when the brakes are not depressed. When the brakes are applied, the warning noise goes away because the indicator has now been forced against the brake rotor and is not able to vibrate which causes this whistling noise.

If you hear brake noises other than a squeal, it could mean your brake pads are worn out and need to be replaced. If your brake pedal feels different than normal or if you've noticed any change in the way your vehicle brakes (pulls to one side when braking or requires more pressure on the brake pedal), have the brake system inspected at once.

What should I do?

What can you do as a customer to reduce the chance of squealing brakes? First of all, noisy brakes should always be inspected to make sure there isn't a problem with the braking system. If the pads have worn down to the point where metal-to-metal contact is occurring, your vehicle may not be able to stop safely, and you may damage the brake rotors or drums to the point where they have to be replaced. If you replace the brake pads yourself, make sure not to contaminate them with grease or brake fluid, as this can cause noises. Sometimes a few harder-than-normal stops can "de-glaze" the brake pads and help reduce the squealing noise for a while.

There are many aftermarket disc brake pads that claim to be "quiet" or have been "designed" for import and front wheel drive vehicles that you can choose from. Personally, I have had the best luck replacing the brake pads on small vehicles like Honda and Toyota with original equipment pads from the dealership rather than using aftermarket brands. It is usually more expensive to purchase these pads from the dealership, but the quality is much better. I am an independent shop owner and my whole business philosophy is to buy as little as possible from dealerships, but after trying many squealing aftermarket brake pads, I have learned my lesson and pay the extra money.

For over 63 years, Austin Davis' family has built a reputation in the auto repair business for being honest, dependable, and for serving customers at a fair price. To help those who can't visit his garage, he's authored "What Your Mechanic Doesn't Want You to Know". You'll find it at http://hop.clickbank.net/hop.cgi?mechanictr/mechanic

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