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Parking brakes are necessities on some vehicles as is their service

While many drivers overlook these instruments, some vehicles make it impossible to do so.
Thursday, October 1, 2009 - 00:00

While many drivers overlook these instruments, some vehicles make it impossible to do so.

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For many drivers, parking brakes are an afterthought — if they're thought of — and that's not good. This too-often overlooked system serves an important purpose. That purpose has nothing to do with emergencies; banish the term "emergency brake" from your vocabulary! The parking brake is there to keep a stopped car where the driver put it, either by itself or backing up the transmission.

Preventing Wear and Other Problems

Want proof too many drivers don't appreciate the importance of parking brakes? Just watch a busy, sloping parking area sometime. How many arriving drivers hop out of vehicles that are still rocking back-and-forth? Too many just select Park and release the footbrake. On an incline this lets the vehicle roll until something stops it. So the parking pawl (with an automatic) catches or meshed gears meet (with an engaged stick) to arrest the motion — but not in one, smooth move. By the time the transmission catches, momentum causes an opposite reaction, rocking the vehicle — sometimes several times. As a car or truck treated this way ages, wear increases the distance and severity of the rocking motion, worsening wear on all parts concerned every time the car rolls when the driver skips using the parking brake.

If anyone you observe letting a car rock and roll because they failed to apply the parking brake happen to be your own customers, be sure to clue them in: Applying the brake costs nothing and can prevent costly driveline problems as well as (ironically) parking brake failure. This can happen when disuse allows cables to corrode and seize — often grounds for a flunked safety inspection.

Not only does parking brake use help preserve harder-to-maintain drivetrain components (as well as the parking brake system itself), on several models the rear brakes won't self-adjust unless the parking brake is used. Besides, parking brakes also mean enough to safety officials that manufacturer-identified parking brake problems often lead to recalls. They shouldn't be ignored.

Variations, Complications

For decades, parking brakes were pretty standard: a strut inside each rear drum brake engaged one shoe web, and in combination with a lever engaging the other web, spread the shoes into contact with the drum when tugged by a cable. Pull for the cable came either from a lever or pedal operated by the driver. Thanks to the simplicity and dependability of the system just described, drum brakes will remain in use for some time. But more modern systems are providing plenty of company.

Adding the parking function to a disc brake has proven both a challenge and opportunity to engineers. Often, carmakers opt for specialization — letting calipers grip rotors only to stop a car that's moving and adding a drum brake dedicated to parking inside the hat section of the rotor. These drum-in-hat systems have been around at least since the four-disc 1966 Corvette.

Mechanically applying a caliper can be tricky, requiring a hole in the blind end of the bore for a moving shaft that then needs to be sealed. Leaks here are possible. In older models we've also seen complications with internal moving parts when brake fluid gets stale and corrosion intrudes.

Sometimes the mechanism for applying a caliper-based parking brake is an electric motor, and electric parking brakes (EPBs) are enabling some upscale carmakers to make parking brakes so easy to use that even the laziest of drivers shouldn't be tempted to ignore them. For example, if the driver of a new Jaguar XF just lifts the parking brake finger switch on the console and then pushes the button that shuts off the engine, the transmission dials itself into Park after the motor-driven parking brakes engage. There's absolutely no rocking and rolling.

That's great news for the entire drivetrain, but it may mean the need for new or updated scan tools in order to retract caliper pistons for simple brake-pad replacements.

If electronic problems develop, scanning is a must. Jaguar had a big problem, leading to a recall of some EPB-equipped 2003 and '04 S-Types. In certain circumstances the parking brakes could self-apply. In some, though not all cases, the parking brake indicator on the instrument panel would illuminate during parking brake self-application.

Recalls Nos. S-166 and S-167 contained details, including the fact that electrical interference caused the problem, which, in some cases, could be fixed by adding suppression equipment. Otherwise the EPB module had to be replaced.

While rolling a disabled vehicle with conventional parking brakes is relatively simple, moving a disabled car with an EPB can present new challenges. While in many cases you may be able to release the brake if battery voltage is present, at other times you may need to resort to OEM specific procedures to release the brake or even drag the car around on a floor jack or dolly.

Chrysler's Time-Saving Tip

When Chrysler issued a TSB regarding a parking brake pedal ratchet problem in 1990-2000 Wranglers, it also included a tip that can save time when you need to detach a parking brake cable and reattach it. The procedure works on many vehicles, not just the Wranglers in question.

Apply the parking brake and clamp locking pliers on both inner cables where they come out of the front ends of their housings. When you release the pedal, there should be slack to slip the front cable out of the retainer. It's still necessary to check adjustment once the parts are reassembled.

Paul Zangari is an SAE member and former ASE-certified automotive tech. Specializing in technical automotive subjects, he hosts a car-care radio show in Providence, R.I., called "Drive-Thru Radio." It airs weekly on station WPRO-AM and is streamed at www.630wpro.com.

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