Why do my brakes squeal? How can I stop it?

March 15, 2021

Have your brakes started to make a weird sound when you drive your car first thing in the morning or when you back up? This can be squeaking, screeching, squealing, or a grinding metal-on-metal sound. Although unpleasant audibly, squealing brakes are common for car owners and can result from a number of different conditions. Fortunately, it might be fairly easy and affordable to fix noisy brakes, depending on the root cause. The key is the frequency of the sound. 

Squealing Brakes Causes

There isn’t a one-size-fits-all solution for noisy brakes because the mechanism responsible for stopping your car consists of many parts, and each of these has to be in good condition. These are the most common reasons for squealing brakes:

Moisture & Surface Rust 

Best case scenario - your car sits overnight (like for most of us), and your brakes develop surface rust from the moisture in the air and condensation from high humidity. The first few times you use your brake pedal, the surface rust is being scraped off the rotors. Squealing in this case usually goes away after a few applications and is nothing to worry about.  

Worn Brake Pads

Now, if the sound your brakes are making is continuous and high-pitched, it might be time to take a look at your brake pads. When you use your brake pedal, the brake pads clamp down on the rotors (the metal discs), creating friction between the material on the brake pad and the rotor. This friction is what stops or slows down the vehicle. Some cars have a built-in indicator of wear on the brake pads - a small steel tab that starts to make a sound when the friction material has worn and the indicator is touching the rotor directly. If your car doesn’t have a built-in indicator, the sound will be similar because the brake pad will wear down to the steel backing and also make contact with the rotor directly. Metal-on-metal is no fun and if you hear this grinding sound, it’s definitely time to replace your brake pads!

Warped Rotors

Another common cause of squealing brakes is uneven wear on the rotors, which we sometimes call warped rotors. This happens when the uneven wear on the rotor won’t let the brake pad press flat on the metal disc, creating vibrations which in turn create noise. The uneven surface of the rotor isn’t as severe as it sounds and is usually caused by high heat. The excessive heat often comes from constant pressure on the brakes, so if you are doing crazy maneuvers in parking lots, don’t be surprised if your brakes start complaining. The vibration can also happen with uneven wear on the brake pads themselves because the mechanism isn’t flush together. Uneven wear on the rotors or brake pads can also result from glazed rotors, which is another root cause of squealing brakes that we cover below.

Sticking Brake Calipers (Glazed Pads and Rotors)

Brake pads clamp down on the rotors through another mechanism called brake calipers. If your calipers are sticking, it means that your brake stays partially applied, even when you are driving. As you can probably guess, the constant contact between the brake pad and the rotor creates excessive heat, some of the brake pad friction material comes off and goes on the rotor. The sound you hear is the continuous contact between the overheated pads and the metal discs. When your brake calipers stick, the pads can also harden and crystallize, or, glaze. There is much less friction between crystallized pads and the rotors which means less powerful brakes, which in turn means danger if you are in an accident. The only way to fix glazed rotors and pads is by replacing the brake pads and resurfacing or fully replacing the rotors as well. 

Loose or Broken Parts

If it’s not surface rust, worn brake pads, warped rotors, or sticking brake calipers, your brakes may be squealing because of loose or broken parts. Because the brake mechanism is complex, there is yet another part that may be responsible for the noise - the brake shims. Insulation shims are installed in the vehicle to insulate the steel backing of the brake pad against the caliper. Eventually, these wear down and need to be replaced. Sometimes, the mechanics can forget to put the new shims on so if you hear a squealing sound right after a new brake job, give your mechanic a call.

The name speaks for itself here - anti-rattle clips loosely hold the brake pad in place so it will not vibrate, rattle, or create any sound when you apply the brakes. If you’re hearing a noise coming from your brakes when you drive, it might mean that these clips are worn, too loose, and need replacing. 

How do I stop my brakes from squealing? 

As soon as you notice any vibration or sound, it’s best to address them. Your brakes will often give you warning signs in this form and if the squealing progresses or you hear metal-on-metal, it means you ignored the first signs of wear. Also, since squealing brakes have so many potential culprits, it’s best to call a mechanic and get a professional inspection. After all, brakes are one of the most important safety features in your vehicle so you want to make sure that yours are ready for anything. As always, it’s best to be proactive than reactive with your car’s maintenance, and keep up a regular schedule of service appointments.