How Does a Car Brake Work?
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Brake Function
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All brakes operate to have the same final effect, to stop rotational motion. The rotational motion, of course, is the wheel. The wheel on your car, truck or any other vehicle propels it forward or backward. The brake operates to slow and then stop the moving mass in a safe and repeatable manner.
Disc or Drum
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Whether your vehicle uses disc brakes, drum brakes or both, they all work on the same principle of absorbing energy. Brakes do more than just slow or stop a car, they actually absorb all the energy that is expended in moving the vehicle. Of course, friction from air and the moving parts in the car all help to constantly slow the vehicle, but the brakes do the majority of the work.
Disc brakes use two pads on either side of the disc rotor, which is mounted to the wheel. When the brake is applied, fluid compresses the brake pads against the rotor disc and absorbs the energy to slow the car.
Drum brakes work in much the same manner. They are pushed against a rotating drum outward. Drum brakes have a larger surface area for absorbing the car's energy. Drum brakes are generally used on the rear wheels of heavier vehicles like trucks and trailers. The heavier the load, the larger the brake must be to absorb the energy.
With Friction Comes Heat
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Constant application of brakes against rotors or drums causes wear and tear on the brakes system, especially the rotor disc and brake drums. The heat that is absorbed must go somewhere, and generally this is the metal that surrounds the brake pads. Rotor discs and brake drums must be inspected every so often for cracks and warps that can occur from improperly adjusted brakes.
Cars and trucks are designed with a balanced load in mind on the four wheels, not only for control in moving forward but also for stopping. All four brakes must be equal in the application of force to slow and stop the vehicle in a straight line. If not, unequal forces will create an imbalance, and more than brake damage may occur to a disc or drum. It can send your car careening out of control.
Automatic Braking System (ABS)
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The Automatic Braking System, or ABS, is now standard on all vehicles. This system uses speed sensors on every wheel that has a brake. The computer reads the speed of all the wheels. When the brake is applied, the pads are pulsed to quickly apply pressure against the rotor to slow the vehicle. A separate, hydraulic pump motor creates the pressure from the fluid to slow the car. You may feel a pulsating in the brake pedal when you apply the brakes on an ABS; this is normal. It is the computer pulsing the brakes to bring the car to an accurate stop.
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