What Causes My Brakes to Squeal?

Sounds like a simple question, right? I have been in various jobs within the auto service world for over 20 years. I asked several of our Parts Experts. They asked their customers... I have several different answers for you.

Brake squeal is basically caused by a metal on metal friction. Since brakes are designed to cause friction to slow down your car, it seems they should squeal all the time. The reality is that the material formulation on every manufacturers brake pads are designed to eliminated the squealing noise. The noise then comes from other metals within the process.

Mechanics HATE brake squeal... it is the number one cause of customer returns and warranty work. The reality however is that most of the time the problem is caused by incorrect installation. Every brake pad set we sell comes with new hardware which should be replaced every time. The shims should also be replaced to keep the back of the pad from rubbing on the caliper piston. Most of you have heard of brake quiet spray... It is designed to spray on the BACK of the pads to cut down on noise, not the pad material or rotor.

Finally, one thing that may be the overlooked step is the cleanup process. There is a large buildup of metal shavings in the entire brake/wheel area that needs to be cleaned up and meticulously kept away from the new brake pads. This same process needs to be done when the rotors are "cut" or shaved down to a new perfectly level surface. The microscopic metal filings must be washed off, with soapy water not brake cleaner, so that they don't transfer to the surface of the new pads. If any of those brake filings get embedded in the pad material, even ceramic, there will be metal on metal and the squeal will happen.

The main thing to pay attention to when doing a brake job needs to be precision and cleanliness, not speed. Saving five minutes today does not make sense if it will cause a disgruntled customer and forty five minutes of your time next week. It's like everything, do it right the first time and things will always be better.

Autopartstomorrow

P.S. You may be thinking to yourself, "What about semi metallic pads?". The metal used there is copper so the "metal on metal" is dissimilar and therefore doesn't make noise. The noise comes from steel on steel in the case of the brake filings and from iron on iron if it is the backs of the pads and the caliper housing.