by Jim Kerr

Of all the car problems that can occur, stopping the car correctly is the most important to everyone’s safety. Noise from our brakes is a warning that every driver should pay attention to. It may be minor, but it could indicate serious safety problems.

You have probably heard cars passing by with unwanted squeals from the brakes of the vehicles. This type of noise can be found on many of the cars driven on the roads today and drivers spend a lot of time and money trying to correct it.

Sometimes a complete brake overhaul is done to try to correct the problem. This typically involves replacing the brake pads on disc brakes, and the brake shoes on drum type brakes. The friction surfaces of the metal brake drums and rotors (the part clamped by the brake pads) are also often machined to provide a flat, smooth surface for the brake friction material to push against. While the brakes may work well, sometimes the squeal comes back shortly thereafter.

The squeaking noise from the disc brakes is caused by the brake pads vibrating at a very high frequency in their mounts as the brake rotor slides past. The noise could be compared to someone sliding their fingernails down a blackboard; a most unpleasant sound!

The squeak or squeal will usually be there when pulling away from a stop, and when pressing on the brake pedal lightly. The noise should stop when stopping the car quickly. If the noise is loud, steady, and there all the time the car is driving, there is a problem with the brakes. It may be a stone trapped in the brake mechanism, a seized or worn brake caliper, or some manufacturers have a metal wear indicator that touches the rotor and squeals to tell you the brake pads are worn out. Vehicles with a constant noise should be checked as soon as
possible by a brake specialist.

Intermittent squeaking noises can be caused by the brake pad materials. In the past, the brake friction material was made out of asbestos. It stopped well and was quiet but the dust generated was extremely bad for our lungs. Today, the material can be classified as organic, or metallic. Brake pads made with organic materials tend to be quiet but wear faster and are not suitable for use where the brakes will be used severely. Metallic linings are used where severe braking conditions will be encountered and high brake heat generated. The metallic material will give better brake performance under severe and repeated braking and can last longer, but makes more noise such as squeals and squeaks.

Manufacturers will use both types of brake friction materials on their cars depending upon the intended or suggested use for the vehicle. Replacing brake pads that were made of organic material with ones made of metallic materials could cause the brakes to squeak. Original equipment brake pad materials are chosen carefully by the manufacturer to reduce noises and increase durability. Aftermarket brake pads may stop as well as the original but sometimes cause noises because they may not be optimally matched to the material of the rotors.

Stopping all brakes squeals is almost impossible, and most manufacturers state in their owner’s manual that some brake squeak is normal. However, there are some ways to reduce the noise.

Some foreign manufacturers use stainless steel shims behind the pads toreduce the vibration, but these shims are not often added to “unshimmed” vehicles. Other causes of brake squeak are loose brake pads in their mounts. Sometimes there are metal tabs that can be bent to tighten the brake pads. Other times the pad becomes loose because of wear on the brake caliper positioning surfaces. Replacing the brake caliper is the only way to correct this problem.

The squeaking noise can sometimes be reduced or eliminated by coating the back side of the pad with an anti-squeak material. Several types of material are sold by the manufacturers of brake parts. Some are like a silicone rubber that cushions the brake pad to the caliper so the pad does not vibrate. Other types of material are like lubricants, that allow the pad to vibrate without squeaking. Do not use ordinary grease to lubricate the back of the pad. The high temperature created by your brakes will quickly burn it off!

Finally, burnishing the brake pads will help to reduce squeals andimprove braking performance. Burnishing involves heating the pads to a high temperature to burn off the glaze on them and seat them to the rotor. This is done by driving the car to a speed of about 70 to 80 kph and then braking to a stop with medium to firm brake force. Repeat the stop about ten times, allowing a full one-minute cooling off period in between stops to avoid overheating the brakes. Naturally, this procedure must be done in a safe and traffic free place. If you don’t feel comfortable doing it, your local brake specialist will be happy to help you.