How to Fix Squeaky Brakes

 If you're contending with squeaky brakes, one of the first things you should do is try to identify the cause of the squeak. You should know that all brakes make some noise sometimes and that the occasional squeak isn't a problem, and a squeaky brake can stop a car just like a silent one can.Most modern brakes use a cast-iron disc squeezed between two brake pads lined with friction material. Some higher-end vehicles use pricey carbon-ceramic discs or even special tungsten carbide coatings on the disc, but your average commuter is going to use big discs of steel.

Under the right conditions, the disc, the pads, and the caliper they're mounted in can start to vibrate in exactly the same way a violin string vibrates when stroked by the instrument’s bow. Most brake squeals occur at a single discrete frequency. The speed of the vehicle and how hard you press down on the left pedal will only change the volume of noise, as the pitch is controlled by the stiffness and mass of the pad and disc.

Inadequate development at the manufacturer level that leaves brake systems prone to noise can usually be overcome by a Saturday mechanic without totally re-engineering the entire system. We can try to damp out the noise, or simply change the resonant frequency of the whole arrangement until it stops singing in any audible frequency. Here's how.

Many brake pads will make a swishing or grinding noise for the first few stops in the morning until the pads warm up and shed any moisture they've accumulated overnight. That hissing or grinding noise on some rainy or dewy mornings is often just the pads sweeping off a thin film of rust that formed on the iron discs, and that's perfectly normal.

The brake pad compound itself can also make some noise. In the past, brake pad friction material contained a lot of asbestos. Asbestos was also highly cancerous to those who worked with it, so the industry has almost completely switched to less dangerous alternatives. Kevlar is one material that's frequently used, but it tends to be dusty.

Today's cars are heavier thanks to ever-increasing safety requirements and a bevy of new features customers want. The need to slow down heavier cars led to the rise of metallics and ceramics in brake pads' friction material. Unfortunately, these can make brakes hiss or even grind a little as you slow down. It's a small price to pay for increased performance.

So all pad noise is fine, right? Not exactly. There's one brake noise you need to pay attention to right away.

Many brake pads have a small finger of spring steel called a wear indicator that will scrape on the disc as the pad reaches its wear limit. This sound tells you that it's time to change pads for fresh, thicker ones before the friction material wears completely away. Let it go for too long, and you'll be trying to grip your metal rotors using the metal backing plates of your pads, which aren't very grippy at all and will damage your brake rotor. Don't write this off as a different kind of brake squeal.

The wear indicator makes more of a ripping-sheet-metal noise, not the single, high-pitched note of a harmless (but irritating) squeak.

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