“My car has an automatic transmission with park, so why do I need a parking brake?”
The parking brake serves as a mechanical emergency backup brake system. Should your hydraulic brakes fail, the parking brake can be used to stop the vehicle.
Many people who have vehicles with automatic transmissions rarely use their parking brake. They simply put the transmission into park to lock the drive wheels when they park their vehicle. Even so, it’s important to use your parking brake periodically.
Using the parking brake regularly helps keep the cables freed up so corrosion can’t accumulate and cause binding. Applying the parking brake also works the self-adjusters in the rear brakes, which helps keep the linings in drum brakes properly adjusted for minimum pedal travel. On cars with four wheel disc brakes and locking rear calipers, using the parking brake keeps the threaded self-adjusting mechanisms inside the rear caliper pistons working freely to compensate for pad wear.
The parking brake system is fairly simple. On vehicles with drum brakes in the rear, applying the parking brake pulls a pair of cables that are attached to arms on the secondary brake shoes. This forces both pairs of shoes outward against the drums to lock the brakes. On four wheel disc brake applications, the disc brake pads are pushed against the rotor by the caliper pistons. This requires either a cam or screw mechanism inside the caliper piston that pushes the piston out and holds it there, or a mini-drum brake inside the rear rotor.
On rear disc brake applications with locking calipers, the adjustment of the parking brake cable is especially important. If the cable is adjusted too tight, there may not be sufficient travel to work the self-adjusters and/or the brakes may drag. If the cable is adjusted too loose, the parking brake may not hold the vehicle. As a rule, most hand levers should travel only about 4 or 5 “clicks” when properly adjusted.
On four-wheel disc brake systems that have “mini-drums” inside the rear rotors, the parking brake works like a conventional drum brake. Pulling on the cable forces the shoes outward against the drum to lock the wheel. But unlike a full-sized drum brake, there’s no self-adjuster mechanism for the star wheel to compensate for shoe wear because one isn’t needed. The only time the parking brake is applied is when the vehicle is at rest so shoe wear is virtually nonexistent. The shoes should last the life of the vehicle — unless the parking brake is binding and causing them to drag. The thickness of the shoe linings doesn’t really matter as long as there is enough lining left to hold the car on an incline with normal cable travel.
On most vehicles, the left and right parking brake cables are attached to a lever linkage called an “equalizer” yoke under the vehicle. The equalizer yoke balances or equalizes the amount of force that’s applied to both cables when the parking brake is applied. 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.
Rust is the main concern with the brake cables and linkage. Rust can cause the cables to bind in their sheaths, preventing the brakes from being applied or released. If one cable freezes up, the equalizer can’t do its job so only one wheel will lock. Though this may not create a problem when the parking brake is used for parking, it could create a serious handling problem should the system ever be called upon for emergency braking. The imbalance would likely cause the one wheel to lock up and skid, possibly throwing the vehicle out of control.
The equalizer linkage can also rust up, interfering with proper application and release. Or it’s hinge pivot can sometimes rust or break loose rendering the parking brake useless. Lubricating the pivot points and brake cables periodically with chassis or brake grease can help protect against corrosion.
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