Lee, S., Jeon, J., Kim, S., Kim, S. et al., "A Study of Low-Frequency and High-Frequency Disc Brake Squeal," SAE Int. J. Passeng. Cars - Mech. Syst. 9(3):1235-1244, 2016, doi:10.4271/2016-01-1944.
When two identical brakes are simultaneously tested on a vehicle chassis dynamometer, very often the left hand brake is found to squeal more or less than the right hand brake, all at different frequencies. This study was performed to develop some understanding of this puzzling phenomenon. It is found that as the wear rate difference between the inner pad and the outer pad increases, low frequency (caliper and knuckle) squeals occur more and more, and as the differential wear becomes larger and larger, high frequency (disc) squeals occur less and less, finally disappearing all together. Discs and calipers are found to affect the differential pad wear, in turn affecting brake squeal generation.