What a Parking Brake Does?
The original designation for a parking brake was to stop the vehicle if the main brake system should fail, which is why it was known as an emergency brake. In modern vehicles, the emergency brake isn't very effective at this task because it cannot adequately stop the vehicle with the small amount of force applied. The parking brake is connected to the rear brakes, which do not exert as much force in braking as the front brakes and will do little to stop a vehicle moving at high speeds.
Most modern applications of the parking brake is to ensure that a parked vehicle stays in place, especially on hills and other declines. When engaged, it locks the wheels in place and works with the parking pawl to ensure that the vehicle doesn't roll away. While a parking brake isn't required to be engaged for the vehicle to stay stopped, it works to prevent your vehicle from rolling, especially on steep inclines, and to reduce stress on the transmission. This is why manufacturers recommend using the parking brake even when the driver doesn't feel like he or she needs it.
When a vehicle's gear shift is put into Park position, a parking pawl is engaged in the transmission. This is a pin that locks the gears into place to prevent them from rotating. The pawl stays in place until the gear shift is moved out of the Park position. The problem with relying on this mechanism for the vehicle is that it puts stress on the transmission constantly, which can result in eventual failure. Manufacturers recommend engaging the parking pawl after using the parking brake. The brake provides additional security and reduces the amount of stress on the transmission and driveline components to prevent costly repairs and parking failure.
Components of a Parking Brake:
A lever to engage and disengage the parking brake, found within the cabin of the vehicle
Steel cables to connect to the main brakes of the vehicle located in the rear, often called a parking brake equalizer
The cable system features a "Y" design that allows a set of cables to be connected to each rear brake. A separate cable attaches to the equalizer or "Y" connection and the lever inside the vehicle. Often, these cables are contained inside an outer shell or shielded. The lever may have a separate button to deactivate the emergency brake. Some foot pedals require you to depress the foot brake twice to deactivate it.