Parking Brakes

PARKING BRAKES ven before we made In order to move, the vehicle would may apply just fine, but refuse to let go the transition from then have to overcome the inertia when the lever is released. To assure horse-drawn vehicles of the engine’s compression. This is that they work properly when need- to automobiles, driv- normally sufficient to keep the vehi- ed, parking brake systems should be ers of carts and bug- cle stationary on level ground, but on inspected on a regular basis. A full in- gies needed a way to an incline, the weight of the vehicle spection should include the following. slow or stop their vehicles quickly may be great enough to overcome If a cable looks rusty on the out- Eor in an emergency. Pulling back on compression. The vehicle would side, spraying it with lubricant will the reins might encourage a horse to then creep forward in increments provide only a temporary fix. The lu- slow down and eventually stop, but as each cylinder’s compression cycle bricant will attract grime, and once additional stopping power would cer- was overcome. Applying the parking it’s inside the sheathing it can destroy tainly be welcome. The first “emer- brake supplements the engine’s hold- the cable. Rusty or damaged cables gency brake” was a lever that applied ing power and negates this possibility. should be replaced. Even if a cable a rubbing block to make contact with In cities with extreme inclines (like looks okay on the outside, the inner the outer circumference of one of wire will stretch over time, especially wheels. Friction slowed the vehicle if the parking brake is frequently ap- and the same lever could be used to plied. This creates slack that increases help hold the vehicle in place once parking brake lever or pedal travel. it was completely stopped. So the Most systems include an adjustment emergency brake served double duty capability to take up some of the as the parking brake as well. stretch, but if you’ve run out of ad- This technology carried over to the justment, the cable must be replaced. first automobiles. Long levers were On some vehicles, any stretch in used to multiply the mechanical ad- the brake cables is automatically com- vantage and increase stopping power. pensated for by a self-adjusting park- Over the years, these first emergency ing brake pedal. The distance from or parking brake levers evolved in- the foot pedal to the equalizer bar is to the assortment of dash-mounted automatically controlled to keep the pedals or center console-mounted Photo courtesy 2F TRW parking brake pedal travel the same Electronic parking brake (EPB) technol- levers we’re familiar with today. Even ogy can be applied to front or rear cal- during the entire life of the shoes. though they’re still occasionally re- ipers. This allows designers to combine If the rear brakes are serviced, ad- ferred to as emergency brakes, most EPB with other vehicle safety systems, justment to the parking brake system would be of very little practical use in such as electronic stability control (ESC). is required. On some vehicles, the an actual emergency. All of the cables and other mechanical shoe-to-drum clearance must be ad- components of conventional parking Drivers of vehicles equipped with brake systems can also be eliminated. justed. Next, the self-adjuster lock- automatic transmissions have little use out pin is removed, followed by fully for their parking brakes under most San Francisco), drivers park their ve- applying and releasing the parking driving conditions. When the vehicle hicles with the front wheels pointed brake pedal three times. Lastly, the is safely parked, the automatic trans- toward the curb. If the parking brake lockout pin is replaced. mission’s internal parking pawl locks should fail, the vehicle will be able to As these systems are designed to the driveshaft and immobilizes the travel forward or backward only until be self-adjusting, very little additional vehicle, taking over the duties of the a tire contacts the curb. cable adjustment is available. Check parking brake. Unless the vehicle is Since parking brakes are infre- for an adjustment at the turnbuckle. parked on a significant incline and quently used by most drivers, they If the cable has already been short- additional holding power is required, most often suffer from neglect rather ened to the maximum point, replace- parking brake use is unnecessary. than overuse. If a parking brake has ment is required. Things aren’t much different for not been used for a very long time, the On most vehicles, the front parking drivers of vehicles equipped with next time it is used may be the first in- brake cable is attached to a pair of manual transmissions. When the ve- dication of a problem. In areas where rear parking brake cables at an equal- hicle is safely parked, the driver se- road salt is used, cables and levers may izer yoke. The equalizer balances the lects a gear (normally 1st or Reverse). rust and bind. So the parking brake amount of force applied to the brakes 36 February 2016 at both rear wheels when the park- caliper pistons applied, even though ed, an electronic system controls the ing brake is engaged. An adjustment the parking brake lever has been re- electrical actuators that are integrated screw may be located on the front ca- leased. Inspect all of these compo- into the wheel brakes. In addition to ble where it connects to the equaliz- nents to assure smooth operation. manual operation via the switch, these er, or where the main cable attaches A growing number of vehicles systems also offer a range of automatic to the parking brake lever. are equipped with electronic park- assistance functions for enhanced safe- The equalizer linkage can rust up ing brakes (EPBs). On these systems, ty and comfort. Various EPB system or the hinge pivot may break loose the parking brake is not activated by solutions are designed for different and disable the parking brake. A worn pulling on a parking brake lever. In- rear axle brake configurations. hinge pivot will allow normal travel The caliper-integrated electric on the lever or pedal, but the parking parking brake (EPB-CI) is a solution brake will not hold the vehicle on a hill. for floating caliper disc brakes. A float- If the vehicle is equipped with rear ing caliper is combined with the com- drum brakes, parking brake cables ponents of an electric parking brake. typically act on levers inside the rear The electrical operation takes place drums. Applying the parking brake via an electronic system integrated in- causes the lever to push the brake to the electronic stability control sys- shoes outward. The shoes contact the tem. The system also consists of two drums and hold the vehicle station- electrical combined calipers as well as ary. Inspection of these components the EPB-specific operation software. would take place during a regular Photo courtesy Continental EPB-DS is a solution for duo-servo This electronic parking brake system is rear brake inspection. Everything designed for use with a conventional brakes, consisting of a self-boosting should apply and release easily. The rear drum brake system. An actuator drum brake, fitted inside the brake rear brake self-adjusting mechanisms applies the rear brake shoes, eliminating disc hat. EPB-DS is used primarily in must be in good condition, to main- the need for parking brake cables and re- premium-class vehicles, sports cars and tain the proper clearance between ducing the need for routine maintenance SUVs, where separating the service or cable replacement. the shoes and drums. brake and the parking brake is partic- On vehicles equipped with rear stead, the parking brake is engaged via ularly important. The system consists disc brakes, the parking brake may a dash-mounted switch, or is automat- of two electrical actuators and an elec- consist of an additional drum brake ically engaged when the transmission tronic system that is either separate or system. This smaller parking brake is shifted into Park. Early EPB sys- integrated into the ESC and has the system is located inside the rear tems featured motors located in the EPB-specific operation software. brake disc “hat.” Applying the park- passenger-side rear wheel well or un- An electric drum brake with or ing brake lever expands the rear der the vehicle. These motors applied without parking brake (EPB-Si) is parking brake shoes, bringing them the parking brake in a conventional a solution for vehicles with drum into contact with the disc hat’s inside manner, using cables. One advantage brakes on the rear axle. EPB-Si is diameter. These systems frequent- was that cable length was reduced and tailored to smaller vehicles that have ly suffer from neglect. A full service some systems adjust cable slack auto- previously been equipped with a me- requires removal of the rear caliper, matically. Later systems completely chanical parking brake. The actuator rear caliper carrier, rear shoes and eliminate the need for brake cables. is adapted to the unchanged drum rear brake disc. Rear backup cameras will soon be brake. The activation of the park- Other rear disc brake-equipped ve- standard equipment on all new pas- ing brake function is then controlled hicles feature a cable-operated park- senger vehicles. An electronic park- electrically by the integrated lever. ing brake system that acts directly on ing brake system could be integrated The electronics are, like the caliper the rear calipers. When the parking with the video signal and automati- version, integrated into the electronic brake lever is applied, the parking cally brake the vehicle if an obstacle stability program.

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