What causes brakes to squeal?

A. All rotating objects have vibration. This vibration can become amplified at specific natural harmonic frequencies. Have you ever noticed a little vibration in your car as you travel at a certain speed on the highway, and then it goes away as you go a little faster? The wheels were passing through one of these harmonics. Brake noise is caused by vibration primarily from the rotor, pad and caliper. The causes are complex and include things like the compressibility of the brake pad, the surface finish of the rotor, the stick-slip oscillation at certain temperatures, rotor dimensional run-out, rotor harmonic frequency and many other factors. Noise attenuation is a complex part of friction development. Power Stop Evolution and Posi-Mold pads feature dual active rubber coated constrained layer shims. The rubber is placed on both the pad side and caliper side of the shim. This helps reduce vibration that can be transmitted from the pad to the vehicle. Noise can be reduced by putting a ...  more