The parking or emergency brake has to perform two distinct jobs. First, it must be able to hold the vehicle on an incline. Second, it must be able to stop a vehicle under a specific distance if the hydraulic brakes have failed. These standards are set by the Department of Transportation (DOT), and the kicker is these standards must be met with the force applied by a little old lady. But, over time, the cables can stretch and the friction materials change their length and thickness, which is why adjustments to the system are required.
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