Like fingernails scraping across a blackboard, disc brake squeal is enough to make anybody's hair stand on end. For some neurological reason that is not fully understood, human beings react negatively to high-pitched squeals like crying babies, sirens and screeching breaks. So if your brakes are squealing, you want the noise to go away.
Brake squealing is produced by high-frequency vibration in the brakes. With disc brakes, vibrations can occur between the pads and rotors; the pads and calipers; the calipers and mounts; and/or within the rotors themselves. With drum brakes, the vibrations can originate between the shoes and the backing plates, and/or within the drums.
The noise is not dangerous as long as there is no metal-to-metal contact, the brakes are working properly and there is adequate lining thickness. But, it sure can be annoying. So, to get rid of it, you first have to figure out what is causing the brake noise.
Complaints about brake squeal became a problem when front-wheel drive and semi-metallic brakes arrived on the scene in the 1980s. Semi-metallic pads are harder than their asbestos counterparts, and thus are more apt to chatter and squeal if there are any irregularities or roughness on the rotor surface, or if you notice looseness between the pads and calipers.
Some types of caliper designs are more apt to be noisy than others. The pads in these calipers may not be held as tightly and/or the caliper itself may move around a lot when the brakes are applied. And, as we said earlier, the greater the play in the system, the greater the tendency to make noise. That's why some new car dealers try to dismiss the problem by telling their customers some noise is "normal", leaving the customer no alternative but to live with the problem or to get it fixed by somebody else.
Trying to fix a squeal problem the wrong way can often make the problem worse. If somebody does a quick brake job and replaces the brake pads but doe snot resurface the rotors, the result can be an even louder squeal. The same can happen if the rotors are resurfaced incorrectly, too quickly or with dull tools. Excessive rotor runout can also cause problems.
The phenolic resins used in many brake pads tend to absorb moisrue during wet rainy weather, especially when a vehicle is parked outdoors overnight. When the brakes are cold, the pads can be noisy until they warm up and dry out. A chirping or squealing noise may be heard when first starting out or when backing up will riding the brake pedal lightly.
There is no fix for this other than to install a different brake of brake pads that hopfully will be less prone to wet noise issues. These include some of the current ceramic brake pad compounds as well as low metallic compounds. Choose a premium brand for best results.
There are aerosol brake noise suppressing products that can provide temporarily relief. When sprayed on BOTH sides of the brake rotors, the chemicals in the product lubricates and quiets the pads until the thin film wears off. How long does it last? Less than 50 to 100 miles depending on how often and how hard the brakes are applies.
CAUTION: NEVER APPLY GREASE, OIL OR WD-40 TO THE BRAKE PADS OR ROTORS. Lubricants such as these will contaminate and ruin the linings, and may result in uneven braking and/or extended braking distances.
One trick that helps is to LIGHTLY resurface the rotors (both sides) with sandpaper. You just want to rough the surface slightly in a random pattern.
Another trick is to apply noise suppressing shims or compound to the BACKS of the brake pads (never the front!). This will help dampen the vibrations that can cause noise.
Replacing the old brake pads with new premium pads (such as ceramic compound pads) can also help quiet noisy brakes. follow the brake suppliers recommendations if you are attempting to replace harder semi-metallic pads with ceramics because this kindo f swap may not be recommended for larger heavier SUVs and performance cars.
One of the leading causes of brake squeal in drum brakes is poor contact between the shoes and drum. Heel and toe contact between the shoe and drum is often the culprit, and the cure is to either replace the shoes with new ones or to resurface the drum slightly to increase its inside diameter. New shoes are ground with a slight eccentric to compensate for drum wear.
This moves the point of contact away from the ends of the shoes toward the middle. In the old days, mechanics used to arc shoes to match their shape to the drum. But, with the concerns about asbestos, shoe grinding is pretty much a thing of the past (although some say it will make a comeback as more and more new cars switch to non-asbestos linings on their drum brakes).