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, and the kicker is these jobs must be accomplished by 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.
You should never estimate when it comes to parking brake adjustments. Backing off an adjuster by feel on some drum applications can get you into trouble. Some of these applications have clearance specifications because the shoe can swell due to moisture or expand at a different rate than the drum and cause brake drag and noise.
If the manual recommends the use of a brake drum measurement and resetting tool, use one. If the manual calls for backing off the adjustment by five teeth, back it off by five teeth, not four or six.
Most modern brake cables have an inner wire that is made of stainless steel and is surrounded by an outer nylon sheath. Some cables have a dry lubricant inside to prevent binding. If you are inspecting brake cables, make sure all of the grommets and boots are in place.
The best way to keep a brake cable moving freely is to leave it alone. Many home remedies can actually shorten the life of the cable. Lubricants and oils can attract grime that can be pulled into the housing. Solvents sprayed on the cables can wash the grime further into the sheathing and can destroy the cable.
Parking brake cables can stretch over time, which creates slack that increases lever or pedal travel. If all the adjustments are maxed out, the cable should be replaced.
Some vehicles will have a self-adjusting parking brake that does not adjust the cables at the wheels, but at the parking brake pedal. This self-adjustment controls the length of cable that travels from the foot pedal under the dash to the equalizer bar. This is designed to keep the parking brake pedal travel the same during the entire life of the shoes. If any work is done to the parking brake at the wheels, adjustment is required.
On some GM full-sized trucks, you must adjust the shoe-to-drum clearance. Next, you will have to remove the self-adjuster lockout pin, fully apply and release the parking brake pedal three times and replace the lockout pin.
These systems have a limited amount of adjustment. Some slack can be taken out of the cable under the vehicle with a turnbuckle, but if the cable is shortened to the maximum point, replacement is required.
On most vehicles, the left and right parking brake cables come together and are attached to a lever linkage called an “equalizer” yoke under the vehicle. The equalizer yoke balances, or equalizes, the amount of force that is applied to both cables when the parking brake is engaged. The equalizer linkage, in turn, is connected to a single cable that runs to the parking brake lever or pedal. An adjustment screw may be located on the front cable where it connects to the equalizer, or where the cable attaches to the parking brake lever.
The equalizer linkage can rust up, interfering with proper application and release. The hinge pivot can also break loose and render the parking brake useless. The typical sign of a worn hinge pivot is normal travel on the lever or pedal, but the parking brake will not hold the car on a hill.
Electronic Parking Brake
A growing number of vehicles are equipped with electronic parking brakes that automatically engage the parking brake when the transmission is shifted into park. This system is great because it can reduce the length of the cable or eliminate cable all together.
If you are doing a brake job on a vehicle with an electronic parking brake, you might need a scan tool with the proper software for the parking brake system or a dedicated tool to reposition the cable retractor or the calipers.
Motors for cable-actuated systems are located in the passenger-side rear wheel well or under the vehicle. Most of these vehicles have procedures in the owner’s manual for disengaging the parking brake manually.
Some systems even have a program built in that adjusts for slack in the system that runs at certain intervals. Some of these systems require the use of a scan tool to adjust the parking brake. Some have procedures that require pressing the lever in a sequence to adjust the system.