Rodney Dangerfield had nothing on parking brakes: They "don't get no respect" either. Even in modern vehicles, rear-drum parking brakes are essentially straight out of the 1960s (or before.) And motorists regularly "diss" them, too – not a wise move.
However, parking brakes have evolved. We won't trace their entire history, but as an example, most Chrysler products used a drum brake at the rear of the transmission for parking well into the 1950s. The system went back many years, and Chrysler wasn't its first (or only) user.One reason the drum-on-the-end-of-the-tranny brake went away is that it relied upon the drivetrain. If you broke a U-joint in your old MoPar, neither the transmission nor the parking brake could hold it.
But the parking brake has evolved in recent times. Some self-adjust, compensating for cable slack. A few have no cables at all, just wiring harnesses. Some four-wheel disc brake systems incorporate a means of expanding the caliper piston or pushing the caliper into contact with the brake pads for parking. And quite a few four-disc vehicles include a mechanical drum brake inside their rear rotors' hats solely for parking. It may seem like added complication, but rotor hubs have hat sections anyway, and manufacturers often find putting a dedicated parking brake there is less complicated than making caliper pistons perform double duty.Worth Using
It can be costly for drivers to ignore their parking brakes. In jurisdictions requiring periodic safety inspections, a working parking brake is usually needed to pass. But motorists who never use theirs run the risk of components binding and inspection failure.
But a bigger incentive is that parking brake use saves wear on costlier components. Drivers who stop, shift into park, then release the service brake may feel used to the sensation of the car rolling, then lurching back-and-forth through driveline play until eventually settling down. But the parking pawl or sprag in the transmission never gets used to it, nor do universal or CV joints. The irony of this is that parking brake use can be, essentially, free. How much friction material wears off when a shoe sits against a drum that's standing still?
With this in mind, let's examine some things that can go wrong with mechanically operated parking brakes.The single-shoe brake
Perhaps the most common parking brake-related situation Bendix Brake Answerman Jay Buckley has been asked about recently involves the single-shoe drum-in-hat parking brakes in recent Chevy Silverado and GMC Sierra pickups.
GM has issued Technical Service Bulletins (TSBs) regarding the parking-brake shoes on these trucks, and Buckley singles out two: the one requiring the use of new hold-downs anytime the rotor is removed and another calling for replacing the shoe with a new one whenever the rotor is removed.
The reason for the bulletins is that the inside of the drum may tug at the shoe as the rotor comes off. If the shoe bends, it won't be flat against its backing plate and may noisily rub inside the drum. Buckley has no quarrel with replacing the hardware when the rotors come off."But that shoe's a pricey item," he notes. "We've found you can check it for flatness. Just place it on a flat surface. If it makes nice, even contact, it's okay for reuse. But if you see it's sprung, you can gently twist the thing so it lies nice and flat on the table. And then you can reuse it – as long as it's not excessively or unevenly worn."
Another matter concerning the 2002 models is early (24-month) wear of the single shoe. GM found that the hold-downs used on the '02 models were too aggressive, preventing the shoe from re-centering after release, leading to uneven wear. Starting with the '03s, hold-down force was reduced on new and replacement hardware.
GM 'W' Body: The Hokey-Pokey
General Motors made a mistake in the design of the parking brake mechanism in the early W-Body cars with four-wheel discs (Lumina, Grand Prix, Cutlass Supreme, Regal). The rear caliper pistons would self-adjust only when the driver released the parking brake. But even drivers who routinely used their parking brakes would run into problems because of how it had to be released.
If an early W-Body's rear brakes go unadjusted too long, the front brakes look bad. This is because eventually the rear pistons seize and quit working. But since the seized pistons limit pedal travel, they mask what would be a giveaway of rear-brake inactivity. Instead, the front brakes wear repeatedly. The fix is not just to replace the worn parts in front, but also the rear calipers.
But repairing the parts won't prevent the problem from recurring unless the driver is educated about parking brake use. And in these cars, drivers don't only need to know they should use the parking brake, they also need to know that rear brake self-adjustment takes place only if the parking brake is released when their foot is off the service brake pedal. Unfortunately, we're all taught to release the parking brake with our foot on the brake pedal.
As a countermeasure, some technicians instruct owners of pre-1995 W-Bodies in a sort of "Saturday Morning Hokey-Pokey." Drivers are told that once a week, with the car on level ground, to sit in the driver's seat with their left foot out of the car and their right foot inside, and to use the right foot to apply the parking brake several times, with the foot on the floor mat each time they release it. A neighbor with a 1991 Lumina learned this drill, and his brake problems went away.
Replace, Don't Fix
General Motors isn't the only manufacturer calling for certain brake parts to be replaced, not serviced. Chrysler doesn't want you to mess with the parking brake actuator levers on the rear brakes of 1997-2000 Voyager, Caravan and Town and Country vans equipped with four wheel discs.
And they're emphatic about it. How's this for flat-out saying "NO!" in a TSB: "DO NOT attempt to repair it." The warning is underlined, capitalized and in bold print as shown. At least they don't just tell you what not to do, the manufacturer also says what should be done: "The park brake actuator/lever must be replaced with p/n 04882584AA whenever service is required."
Talk about speaking plainly!
