Change When They Look Worn
A quick visual check of the brake pads, including a quick measurement of the remaining pad, can determine whether the pads need replacing. Most mechanics advise that if a pad has below 2/32 of an inch left, it should be replaced.
Change at the Sound of the Metal Indicator
Most drivers wait until they hear the sound of the metal wear indicator, which can only be heard after the brake pad is worn. This is a solid indicator that the brake pads are worn heavily and need to be replaced. You do not need to visually inspect the pads for wear when the sounds is evident. Many mechanics advise that brake shoes be replaced whenever the brake pads are changed, regardless of wear.
Brake pads and shoes can last upward of 50,000 mile on some vehicles and as little as 10,000 miles on others. The length of time between changing your brake pads and shoes often depends on your driving style, the quality of your brake pads and shoes, vehicle weight and road conditions. The visual method of inspecting the brake pads for wear below 2/32 of an inch will guarantee that you'll know the pad needs replacing before the metal wear indicator can cut into the rotors, resulting in further damage and higher replacement costs.