Since brake pads (and shoes) are actually wear items and not maintenance items, they don’t need to be replaced at a specific mileage or time interval. However continues driving on brake pads that are worn out could result in additional component failure, resulting in additional repair expense. How much additional expense depends on how long the car owner takes to replace worn out pads, as well as the type of vehicle.
The Pitfalls of Worn Out Brakes
When the brake pedal is applied, the brake pads are hydraulically applied to the metal rotor. The pads have a material that wears as they are applied to the rotor. If the pads go unchecked, the wear material will eventually disappear and the pad will become bare metal. The bare metal on metal reaction can damage the rotor to the point they need to be replaced.
Due to the added heat caused by the metal-to-metal friction, other brake components could also be damaged. Some of the additional components that may be determinately affected include
Routine Maintenance and Brake Inspection
Naturally one of the best methods to determine if your pads need to be replaced is to have an automotive technician inspect them. The best time for a tech to inspect your brakes is when the tires need to be rotated during a routine maintenance visit. Most auto shops will inspect the pad thickness for free since they already have the wheels/tires removed for the rotation.
During an inspection, the pad thickness is measured (in inches or millimeters) and should be replaced if they fall below a specific measurement. The measurement can vary but usually should be replaced if they fall roughly below 3/32nds of an inch or 3 millimeters. If the measurement is greater than this amount the technician should give a rough estimated of how many miles are left on the pads.
Tell Tale Signs of Worn Out Brake Pads
Some (not all) vehicles have a wear indicator that will give an audible sound when the pads wear to the point they need replacement. More sophisticated vehicles may have a ‘visual indictor. The owner’s manual should indicate if a specific vehicle has brake wear sensors.
If the pads or shoes are worn down to the metal, a metallic grinding sound will usually result when applying the brake pedal. If this type of noise is apparent when the pedal is applied, the vehicle should be inspected immediately. A metal-to-metal condition will also result in less effective braking condition. This condition can often be felt when applying the brake pedal.
Source: car fire experts