The parking brake is an essential safety device on automobiles and operates mechanically when the brakes fail or to safely hold an automobile in place when parked. Most parking brakes on later model vehicles utilize the rear brakes and rotors. A series of cables running from the pull handle or parking brake pedal is used to bypass the hydraulics of the normal braking system; but when the rotors have a problem, the parking brakes can fail.
Worn Rotors
Since the rear rotors of the disc brakes are used for the parking brake system, the same problems that occur with the disc brakes happen with the parking brake. The parking brake cable controls the calipers of the rear brakes, and the rotors can wear down, preventing the calipers from applying enough pressure to the rotors to stop the vehicle. The rotors are a wearable component of the automobile and do need to be inspected each time scheduled maintenance is performed on the vehicle. The brake shoes wear a groove into the rotors under normal driving conditions; and if the rotors are not inspected periodically, the rotors will become worn.
Glazed Rotors
The rotors on the brakes can become glazed and prevent the parking brake from working properly or slip. This glazing happens to the rotors when the braking system becomes too hot or overheats because the brake shoes are worn. A glazed brake rotor does not allow the brake shoes to hold tight because the rotor's surface has become smooth like glass. Once the parking brake is applied, the calipers will tighten the brake shoes against the rotors; but since the rotors are glazed, the parking brake will not hold the automobile in place. If the rotors are glazed from overheating, they can be machined down to bring the surfaces back or will need to be replaced.
Warped Rotors
The parking brake will not hold the automobile if the rotors are warped. The rotors become warped when the automobile brakes are operated at an excessively high temperature which takes the rotors past glazing and to the point where their diameters warp. This rotor problem is created because of a problem with the brake shoes rubbing against the rotors during normal driving conditions. The heat builds up on the rotors, causing them to glaze and then warp. Once the rotors are warped, the brake shoes do not press down onto a flat surface because of the warping. Once the parking brake is engaged, the brakes will slip, allowing the automobile to roll freely. The rotors need to be replaced if they become warped.
