Squeaky brakes are one of the easiest automotive maintenance symptoms to recognize. The sound of a squealing brake pad on most cars is pretty unmistakable. However, what causes your brakes to squeal? And does squealing mean it's always time to schedule a brake service and install more pads? The answers to these questions can be a little more nuanced than you might expect.

Why Are Your Brake Pads Squealing?

There's generally only one reason that brake pads squeal: metal-on-metal contact. Modern disc brakes use steel discs (or rotors) as a friction surface for the brake pads. Manufacturers use different friction materials in their brake pads, but they usually contain relatively little (or no) metallic content. As a result, there's not much noise when the pads and the rotors come into contact.

However, all manufacturers install a special metal wear strip in their pads. The friction material wears down and exposes this wear strip, allowing it to make direct contact with the rotors. This wear indicator is typically the sound you hear when older brakes start squealing. In other words, that annoying sound is an intentional design feature.

Of course, almost any metal touching the rotors will produce similar sounds. You may also hear squealing if your brake pads are loose, allowing the metal to vibrate or touch the rotor. Insufficient lubrication, installation mistakes, or dragging calipers are other potential causes for squealing brakes other than normal wear and tear.

Are Squealing Brakes Dangerous?

Minimum pad thickness may vary slightly between manufacturers, but most will install wear indicators at around a 3mm depth. Pads with a few millimeters of thickness remaining will continue to operate safely, but this depth indicates that there's not much friction material on your pads. Once the pads degrade far enough, the backing plates will begin to rub on the rotors, causing grinding and damage.

In some cases, brakes may squeal when there's still plenty of material left, but it can be hard to check without removing a wheel and measuring the pad thickness. If you're not comfortable performing this inspection yourself, you should consider squealing pads as a warning sign that your car requires the attention of a professional.

Once you hear your brakes squealing, it's a good idea to have a brake shop take a closer look. If your brakes don't require immediate service, the technician will still be able to measure your remaining pad thickness and provide you with an estimate of how long they should last. However, if they do require attention, servicing them now can help you avoid reduced braking performance and costly damage.

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