It can be frightening when you press down on the brakes of your car and you hear a loud squeal. It makes you worry that your brakes are going to give out or that you're going to need to spend a lot of money fixing your car. Not all causes of brake squealing are extremely dangerous to your car, but you should always get problematic aspects of your vehicle checked out to play things safe.
The main cause of brake squeal is the high frequency vibrations that occur when your brake pads contact your rotors. If there are irregularities on the surface of the rotors, the brake pads will bounce as they hit the rotor, which begins the vibration. This vibration goes up the calipers and caliper pistons to create a squealing sound. The greater the vibrations the louder the squeal will be. Most factors that cause brake squealing are causing this vibration to happen. If your brakes are worn down, you may have to get them replaced, but if your brakes are new, you may just need to have your brakes tightened.
Over the course of a few years, dust can build up and cause squealing brakes. When the shoes of your brakes wear down, dust starts to coat the drums and cause the vibration that leads to squealing. When this dusty drum is combined with certain weather conditions, such as cold weather and early-morning dew, this can make the brakes sound like they are in bad shape. There are dust and contaminant removing products available for brakes to help with this problem.
Broken Anti-Rattle Clips
Where the brake pad is connected to the caliper, there are protective items called pad stays. These pad stays are connected to anti-rattle clips that help to prevent the vibration of the brakes. When the clips wear out or break, the vibration begins and the application of the brakes will cause a squeaking sound. To deal with this problem you need to have the clips replaced.
When a car is newly produced from the factory, there are pads called insulation shims put against the back of the pad to keep it insulated. If there is not enough padding between the pad and the brake caliper, there will be a squeal. Sometimes these shims are discarded during a brake job or they will wear out. If they wear down or are removed, you will need some type of insulation in their place. You can get new shims or a silicone insulation gel. If you have just got your car back from the shop and notice a squealing, it probably has to do with the shims.
After a brake job, your brake rotors need to be resurfaced to avoid the squealing of a vibrating brake. Returning the rotor surface to this state is called returning it to "true." If the rotor surface is not returned to "true" it will begin to vibrate, cause a clicking noise, or break the anti-rattle caps. This is another potential cause of squeaking that may occur after you've got your car back from the shop.