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FleetMaintenance_NovemberDecember_2016

tion components, actuation systems and medium and heavy duty aft ermarket parts for medium and heavy duty commercial vehicles (www.foundationbrakes. com). “Th e decision on air disc versus drum brakes typically comes down to a total cost of ownership decision,” Oreskovic adds. According to Joey Campbell, manager, engineering, air disc brake, Bendix Spicer Foundation Brake, there are both some distinct similarities and notable diff erences between the types of medium duty brakes found on commercial vehicles today: AIR DISC BRAKES Air is supplied from the vehicle’s braking system to the individual wheel ends, where an air chamber or actuator is employed to translate the air pressure into a mechanical force. Th at force is then applied to the disc brake, which amplifi es the force and clamps two pads onto the rotor to slow a vehicle’s speed. DRUM BRAKES Force applied to the drum brake is created by an air chamber, as with an air disc brake. However, with a drum brake, the air chamber applies the mechanical force to a slack adjustor, which promptly creates a torque that is applied to the S-cam. When that S-cam rotates, the brake linings are pressed against the interior of the wheel hub to slow the vehicle. DISC/DRUM HYDRAULIC BRAKES Hydraulic fl uid is utilized instead of air to apply pressure. Because fl uid can handle higher pressure, hydraulics typically apply a force directly to a disc or a drum brake. For example, hydraulic pressure is employed to push disc brake pads against the rotor. Th ere is no fl uid equivalent of an actuator. DISC VERSUS DRUM Drum brakes are commonly found on medium duty vehicles because they are less expensive than their counterparts, and because it is easier to incorporate a parking brake into a drum, states Steve Ruiz, vice president of engineering, research and development, Centric Parts, a provider of aft ermarket brake systems and replacement parts (www.centricparts.com). However, says Bendix’s Oreskovic, more and more fl eets are employing vehicles equipped with air disc brakes for a variety of reasons. “Air disc brakes provide better performance in that a more consistent torque is generated and vehicles are typically able to stop quicker,” she says. “Air disc brakes also off er the advantages of quicker pad replacement and longer brake lining life, which means greater uptime and lower maintenance costs.” Fleets are also fi nding that they provide a carlike feel and straighter, more stable stops. “Additionally, air disc brakes include an internal self-adjustment mechanism that can help lower the risk of brakes being found out of adjustment during inspection, which can aff ect Compliance, Safety, Accountability (CSA) scoring,” adds Oreskovic. CSA is a Federal Motor Carrier Safety Administration safety compliance and enforcement program. It utilizes commercial vehicle inspections and crash results to assess the safety performance of motor carriers. “Disc brake components are generally lighter and much more effi cient in operation, allowing better braking performance, greater modulation and superior heat dissipation over drum systems,” adds Ruiz. Medium Duty | An alternative to drum brake designs, air disc brakes offer better performance, ease of maintenance and lighter weight. Photo courtesy of WABCO MAINTENANCE CONSIDERATIONS Proper preventive maintenance is critical to fl eets being able to get the most out of their braking systems and components. Fleets must make an eff ort to check brake pad thickness based on vehicle use, during maintenance intervals, as well as within the context of applicable local laws and regulations. Corrosion and buildup of debris on braking systems is always a concern for fl eets, so maintenance professionals must be sure to change the pad and caliper-mounting hardware, plus lubricate any pins or slides appropriately with high-temperature brake grease during the process of changing pads, recommend brake manufacturers. Fleets need to be assured that they own vehicles equipped with the most appropriate brakes for the applications in which they are used. Photo from IStock The case for air disc brakes Air disc brakes offer several advantages over traditional drum brakes, say offi cials at WABCO, a global supplier of technologies and services that improve the safety, effi ciency and connectivity of commercial vehicles (www.wabco-auto.com). SUCH ADVANTAGES INCLUDE: • Stable braking performance. • Virtually no fading and/or pulling. • Excellent downhill performance. • Reduced stopping distance. • Improved driver comfort. “Additionally, air disc brakes are more reliable than drum brakes, which require more maintenance,” say the offi cials. Fleets should keep the these considerations in mind when evaluating air disc brakes and comparing them to conventional drum brakes: • Air disc brakes provide a stopping distance that is up to 15 percent better than that required by Federal Motor Vehicle Safety Standard 121, Air Brake Systems, (FMVSS 121) and 10 percent better than drum brakes. • Air disc brake adjustment is done internally, resulting in fewer Compliance, Safety and Accountability (CSA) violations by eliminating out-of-adjustment situations. • Air disc brake service intervals are up to twice as long as drum brakes. It is estimated that the brake pads of four air disc brake wheel ends can be exchanged in the time of one drum lining wheel end. Air disc brake pads, by some estimates, need servicing every 500,000 to 600,000 miles and rotors up to one million miles. THERE ARE DISTINCT SIMILARITIES and notable differences. Continued Page 26 VehicleServicePros.com ❚ NOVEMBER/DECEMBER 2016 ❚ FLEET MAINTENANCE 25


FleetMaintenance_NovemberDecember_2016
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