For that reason it's important to check those surfaces routinely and eventually replace them when they become so worn they lose some of their effectiveness. Whether you intend to undertake brake repair and servicing yourself or you prefer to leave it to the professionals who work on brakes all day long, it's beneficial to understand some of the processes involved and how the parts in the system work in relation to one another. Drum brakes were the first style of brakes used on automobiles, and on early models only the rear-axle wheels were equipped with brakes. On later vehicles drums were added on the front as well. That pressure is what slows a moving vehicle to a stop or holds a stationary vehicle immobile as long as the brake is applied.
Disc brakes are a more recent development.
They bring a vehicle to a stop by applying pressure to both sides of a disc-shaped rotor situated at the ends of the axle. When the brake is applied, the caliper squeezes the pads against both sides of the rotor to slow and stop the vehicle. Because of their relatively slim design, air can circulate easily around the disc brakes, helping to cool them from friction. The cooling ability is part of what contributes to the overall efficiency of the disc system. Replacement of brake pads is part of regular brake service.