What’s Making Your Brakes Squeal

There are a lot of gearheads that know a lot about mechanics, but there’s one thing that’s still a mystery to a lot of them. Even people who regularly work on their own vehicles often don’t know what makes brakes squeal.

If you’re in that camp, then this post is for you. We’re breaking down what makes brakes squeal so you can enjoy listening to the purr of the engine instead. 

Mechanics of Brake Squealing

When brakes squeal it’s because the energy of motion in the tires is converted into heat and vibrations. This heat and vibration dissipates through the brake system causing a squealing sound. The spinning brake rotor is what acts as an amplifier for the squealing. 

The squealing is the result of something called the stick-slip phenomenon. Stick-slip is something no engineer ever wants to hear. As you may expect, it involves sticking and slipping between the surfaces of the brake pads and rotors. It goes from stick phase to slip phase in an oscillating manner.

When the brakes are applied the brake pads rub up against the rotors creating friction. The friction is both static and kinetic. It’s static in the stick phase and kinetic in the slip phase. This friction is caused by roughness on the surface of the brake pads and rotors that disturb smooth motion. 

The rougher a surface is the more friction it will create. The slower the velocity of the moving parts is the more noise there will be because it allows for more stick time, which causes more displacement and more amplitude of the vibrations. That’s why you may notice that brake squealing is most noticeable when braking at slow speeds.

Bigger rotors and brake pads can also mean more squealing simply because the surfaces are larger and creating more friction. 

Brake Squeals Indicate Vibrations, Not Necessarily Problems

Often when people hear squealing brakes they think there’s something wrong. While squealing brakes can indicate an auto issue that needs to be repaired, it’s actually an indication of vibrations more than anything else. 

Virbrations make a wide range of sounds. All materials have a natural frequency when they vibrate.

In the brake system there isn’t just one frequency. Each moving component is a frequency source. When different parts are vibrating it’s called coupled frequencies. Coupled frequencies are compounded and more complex when compared to a single frequency.

How Operating Conditions Effect Brake Squealing

Because vehicles are operated out on the road all over the planet and not in a climate-controlled, protected environment, the operating conditions have a huge impact on the brake system’s coupled frequencies and the squealing that may be heard. 

Operating conditions that can have an effect on the stick-slip process include:

• Temperature
• Moisture 
• Humidity
• Wear from use
• Corrosion 

Brake systems that can operate at high friction levels within a wide operating temperature range can mitigate the effects of these elements. Countermeasures can also be taken within the brake system to dampen the squealing. 

Tons of Unknowns on the Road

There is literally no way to anticipate every single operating scenario for a vehicle. For that reason, it’s impossible to account for everything that could influence the stick-slip process. It’s simply going to happen, which means some brake squealing is inevitable. 

If your brakes are squealing, come to German Auto Center to figure out if it’s something that needs fixing or is just a part of the stick-slip noise. Our technicians will do a thorough inspection to ensure the source of the squealing is found. Come by the shop or give us a call to schedule a time to have your vehicle looked at by one of our experienced mechanics.