The brakes on an automobile work on fluid pressure. When the pedal is depressed, it activates a plunger in the master cylinder, which pressurizes the brake fluid in the lines, causing the brake components to move. Brake fluid has a very high resistance to pressure, and therefore does not compress well, which is why it is ideal to use in braking systems. Therefore, a brake system that has leaks or air bubbles will not operate correctly, or not at all. It is very important that system leaks be taken care of promptly, because of the risk involved.
Disc brake systems are comprised of two pads per wheel, which clamp down on a spinning rotor when the brake pedal is depressed. When the fluid becomes pressurized, it sends a plunger in the caliper forward, forcing the brakes on either side of the rotor to squeeze it, which results in the slowing and stopping of the automobile. Disc brakes are superior to drum brakes in that they dissipate heat quickly and efficiently, reducing the risk of glazed pads and brake failure. Rotors with holes in them cool down even quicker than the stock units, and are available for most applications. Over time, the pads wear out and need replacement.
Drum brakes operate on the same theory as disc brakes, but with a different design. They both use friction to slow and stop the automobile, but drum brakes employ shoes, instead of pads, to get the job done. The shoes are inside of the steel brake drum itself, which spins with the wheel. When brake pressure is applied, a component called the wheel cylinder expands, forcing the brake shoes apart and toward the inside edge of the drum. This friction works to slow and stop the vehicle. While disc brakes cool down quicker, drum brakes generally have more surface area, and therefore more stopping power, which makes them ideal for vehicles that tow trailers.
