Many car manufacturers recommend replacing the brake pads on your car whenever the lining has worn out down to 1/8-inches or less. You can actually remove the tire and wheel assembly and measure the lining on the brake pad using a rule. However, here are some other important facts about brake pads that will help you determine when to replace and inspect them to keep yourself safe on the road.
The sound the brakes make when applied is another way to tell it is time for new pads. Brake pads come equipped with a pad wear sensor. This small metal tab rubs against the brake rotor when the friction pad wears out too thin, usually about 1/8-inches from its mounting outboard. The sensor will emit a loud squeal, letting you know is time to replace the pads.
Waiting for the wear pad sensor to squeal may damage the brake rotor if the brake pads are not replaced soon afterwards. Most vehicle owners drive within the city in moderate traffic, which means they should inspect their brake pads for wear at least every 12,000 miles or 12 months of driving. However, if you drive mostly in heavy traffic, with frequent stops, you should check for pad wear every nine months or sooner.
Every time you apply the brakes on your vehicle when driving, you wear the lining on the brake pads. As you depress the brake pedal, you are actually operating the master cylinder and brake booster. The master cylinder contains a set of pistons that builds pressure on the brake fluid. The booster helps multiply this pressure on the fluid inside the brake lines. The lines transmit this pressure to the brake caliper and pads on the wheel assemblies. As the caliper pushes the brake pads against the rotor, the friction produced allows the pads to slow or stop the vehicle.
Brake pads are made of friction lining riveted or glued to a steel plate. The lining itself may be organic material or semi-metallic filler. Brake pads containing semi-metallic material are highly resistant to heat, which make them very useful on fleet vehicles used on delivery routs that require very frequent stops. These newer types of brake pads are replacing lining pads made of asbestos.
This is a good reason to take precautions when replacing brake pads on your vehicle. Make sure not to breathe the brake lining dust surrounding the wheel and hub assemblies if you do not know what type of lining was used on these particular pads. According to James E. Duffy in Modern Automotive Technology, older brake pads are made of asbestos, which is known to cause cancer if inhaled in large quantities. Clean as much friction dust from the assemblies using brake parts cleaner and shop towels before proceeding to change the pads.