A parking or emergency brake is simply a mechanical actuation of a car's braking system. Instead of using hydraulic pressure, it uses cable tension and leverage to activate the braking components. This system is usually only used in the rear braking system of cars to facilitate in parking on uneven ground or stopping if there is a loss of hydraulic pressure. The cable is actuated by a hand lever or a parking brake pedal. The cable then runs to the rear brakes of the car. Pulling the lever or pressing the pedal adds tension to the cable, which then activates either the pads or shoes to contact their surfaces creating friction. On many cars this system is self adjusting from the factory and compensates for pad or shoe wear. On others it is manually adjustable by altering the preset cable tension.