Mercedes-Benz ML550 Parking Brake System Adjust Cost

The parking brake is used to secure the vehicle while the vehicle is not in motion and unattended. It is typically secured by using a lever in the vehicle to pull the parking brake cable which sets the brake. Many modern vehicles are moving to an electronic parking brake, which uses an electric motor to set the parking brake when the driver presses a button. Adjustments are necessary when the brake no longer holds the vehicle, or if the parking brake is causing braking force while driving.

There are a few different types of parking brakes, but they are all actuated in the same way. A lever or electronic switch in the vehicle is pulled or pressed, and this will either pull the parking brake cable or signal the parking brake motor to set the brake. Whether or not the vehicle uses a park brake cable or park brake motor, using the lever or button will cause the park brake to secure the brakes, normally at the rear wheels. Drum brake and auxiliary drum brake vehicles will press the brake shoes out against the inner liner of the brake drum, and disc brakes without auxiliary brake drums will squeeze the brake pads against the brake rotor.

It may seem obvious that the only issue a parking brake can create is that it does not hold the vehicle, or does not release the wheels. However, there are several other indicators a technician will look for when diagnosing these two symptoms. The park brake lever may have no tension when pressed, there may be brake noise when driving the vehicle, the electronic park brake button may not be illuminated, or the sound of the relay clicking is not heard when the button is pressed, and there may be physical damage evident upon inspection. All of these symptoms will point to a likely cause during inspection.

The parking brake should always be repaired right away. Even for vehicles with manual transmissions, the parking brake is still essential to ensure safety and security when the vehicle is parked. Since the parking brake can also refuse to disengage, the vehicle may be rendered useless, as the rear wheels may not rotate or the rear brakes may overheat immediately causing wheel bearing and brake damage. When any safety component is damaged, it should be addressed without delay.

Adjusting the parking brake on vehicles with auxiliary drum brakes and disc brake parking brakes should never need to be done. They are self adjusting, and the auxiliary parking brake should never experience wear. For drum service brakes, the drum brakes must be cleaned and adjusted, and the service interval will depend on the vehicle. Most drum brakes are self adjusting, but the parking brake may require additional adjustment at some point before the drum brakes require replacement. This means the maximum a parking brake on a drum brake vehicle should go between adjustments should be around 60,000-70,000 miles.

Parking brake adjustment is needed when the technician identifies that the parking brake will not hold the vehicle when idling in drive and reverse, or when the parking brake will not release to wheels. When either of the factors occur, the technician must visibly and hands-on inspect the parking brake assembly at the wheels or at the lever, and identify the cause of malfunction. When the brakes are out of adjustment but otherwise perform properly, the technician will advise adjustment before any other work is performed.

Adjusting the parking brake will typically only require the cable to be slightly shortened by loosening a pinch nut on the parking brake cable adjuster and turning the adjusting screw until the cable has the proper amount of tension. For drum service brakes, the wheels and drums will need to be removed, the brakes cleaned, and the service brakes adjusted prior to adjusting the parking brake cable. This will ensure that the parking brake is not failing due unadjusted service brakes.

We recommend correcting brake issues before adjusting the parking brake. If the brakes are working inefficiently, the parking brake is likely suffering as a result, and over adjusting the parking brake may lead to excess brake wear and heat. This is most common in drum service brakes, and it is most common that the parking brake is corrected once the brakes are repaired or maintained.

When adjusting a parking brake it is necessary to remove any drum brake or auxiliary drum brake to ensure the parking brake or service brake pads are serviceable. When a parking brake fails to operate or fails to release, inspection is mandatory to identify the cause. This will prevent erroneous repairs and repeat failures.

Adjusting the parking brake should be simple on most models, especially when the parking brake cable adjustment is exterior of the brake drum assembly or for disc brake parking brake systems. It should be noted that some parking brakes are adjusted from within the brake drum, and removing a brake drum which has not received proper maintenance can prove difficult or almost impossible. Further, if the parking brake is seized in the closed position, it may require a technician who has an excellent understanding of the system to remove the brake drum and find the issue.