The parking brake cable is held in a fixed position, and when the parking brake lever is pulled, pressed, or electronically engaged, the parking brake cable is pulled tight. Many modern vehicles with rear disc brakes have an auxiliary drum brake inside the brake rotor that is actuated by the parking brake cable. This protects the service brakes if the parking brake is left engaged while driving. They work like a typical drum brake, but are about half the size, meaning they do not produce enough braking force to stop the vehicle. They do, however, produce sufficient holding force to prevent the vehicle from rolling.

When setting the parking brake does not result in the wheels fully locking, the lever may feel normal, or may be far easier to press or pull than normal. You may notice the vehicle tries to roll, and is stopped by the transmission. Upon restarting the vehicle, moving the selector lever from park may be very difficult, and produce a loud clunking sound as the lever snaps from park to reverse. This is particularly dangerous for manual transmission vehicles, as the transmission does not have a secondary lock, and the weight of the vehicle may allow it to roll, even if the gear selector is placed in a forward or reverse gear. vehicles with electronically actuated parking brakes may display a warning on the drivers information center, alerting to the danger of the failed parking brake. Lastly, the parking lever can fail to return to the disengaged position after released. In this situation the lever will exhibit a total loss of tension, but may provide resistance if manually pressed or pulled into the disengaged position. »MORE: Parking brake show symptoms

It is not safe to operate any vehicle with any braking problem. If there exists any sign that the brakes are not performing as originally intended, the vehicle should immediately be placed out of service, and repaired. If the parking brake does not function properly, this could be a sign of rear brake failure, or, at a minimum, cause the hazard of a runaway vehicle. When the vehicle is parked prior to repair, the wheels should be blocked from movement by a sturdy piece of material. This is normally a piece of wood, or a chock block.

Replacement of the auxiliary parking brake pads will never occur on most vehicles, however, the main cause of failure is driving with the parking brake engaged, or auxiliary brake shoe retaining hardware breakage. These occur at all ranges of mileage and vehicle age because they are normally due to misuse of the parking brake. When the rear service brakes are changed, the auxiliary brake shoes will not normally require replacement, as they do not show normal wear patterns. This is because, normally, they do not contact the auxiliary brake drum while the vehicle is in motion.

If the parking brake lever fails to engage the parking brake, the parking brake cable is normally out of adjustment, however, this could also be the result of a damaged parking brake. If the parking brake cable is intact, and properly adjusted, yet the parking brakes do not engage, a failed parking brake is most likely the culprit. This will be noted as the parking brake will actuate at the wheel, but not sufficiently to hold the vehicle while in gear or on a hill. If this is the case, the wheel and tire must be removed, followed by the brake caliper, brake caliper bracket, and finally the rear brake rotor, which contains the auxiliary brake drum. Upon removal of these components, any breakage or wear patterns may be immediately noticed by the servicing technician.

Replacement is typically a dirty job, as the auxiliary parking brake is mounted to the service brakes, therefore being subjected to road grime, brake dust, high temperatures, moisture, and salt. The rear wheels must be removed to allow access to the brakes. Afterwards, the rear brake caliper must be removed from the rear brake caliper mounting bracket, and then the rear brake caliper mounting bracket must be removed. The rear brake caliper must be hung out of the way to prevent damage to brake lines. Once these items are out of the way, the combination rear brake rotor and auxiliary drum, which is one individual component, is removed, exposing the auxiliary parking brake shoes and mounting hardware. In cases of extreme damage or wear, this may prove to be an extremely difficult task. The brake shoes and mounting hardware are then removed, and replaced. If wear or grooving are noted on the inner lining of the auxiliary brake drum, the rear service brakes must be replaced as well to ensure proper parking brake operation. Installation is the reverse order of these operations, and, if necessary, adjustment of the parking brake cable is performed before the vehicle is returned to the ground.

The entire braking system should be inspected for proper operation whenever the Parking Brake system has been serviced.

The service brakes do not typically need servicing for this replacement, however, if the auxiliary drum parking brakes show signs of wear, the service brakes may require a full service replacement. If the parking brake failed to completely release, the auxiliary parking brakes may need full servicing as the brakes will experience wear, grooving, and extreme temperatures. Some parking brakes are adjusted automatically when the brake is used. This means that failure to set the parking brake over a long period of time may cause the parking brake to fail, and manual adjustment may be necessary if repeated attempts to set the brake do not bring the cable back into proper adjustment. To avoid this, always set the parking brake, whether or not the vehicle is parked on a hill.

The cost of auxiliary parking brakes will vary by vehicle and type. Auxiliary parking brake drums cannot be resurfaced, as most resurfacing machines do not have the capability to reach into the tiny drums, as well they are not made with sufficient thickness to properly machine. This means if the parking brake is left on for any extended period of time, the rear service brakes and parking brakes will need a complete brake service. To avoid this, ensure the parking brake is fully disengaged every time the vehicle is driven.