Truck Parts and Service | Heavy Duty Trucking, Aftermarket, Service Info
Issue link: http://read.dmtmag.com/i/712830
material outward, disc brakes work almost in the inverse, clamping friction- lined brake pads around on a rotor to slow a wheel end. Status quo in the automotive industry for decades, disc brake systems can use hydraulic or air pressure to force a brake pad inward and initiate a stop. The auto- motive industry prefers the former, while the commercial vehicle market is partial to the latter. The system's benefi ts are extensive. One major advantage is the simple openness of a disc brake system. Disc brakes don't operate within a closed en- vironment like drum brakes, allowing for more natural air fl ow during a braking event to dissipate heat. This eliminates brake fade, the phe- nomena that occurs when the extreme heat created during a drum brake stopping event causes the surfaces of the drum and brake shoe to expand, and weakens the contact between both surfaces. The clamping motion of the disc brake is benefi cial here as well. Once engaged, a disc brake works similar to pliers or any other clamping tool. As more force is applied behind each pad the clamping power of the entire system increases. It is that ability to maintain a tight grip on a rotor that allows the system to reduce stopping distances, says Morrison. Bill Hicks, director of Product Planning – Americas at SAF-Holland, says most air disc brake systems have the abil- ity to not only "meet but exceed" reduced stopping distance (RSD) requirements set by the National Highway Transportation Safety Administration (NHTSA) in 2012. And unlike drum brakes, which moved to larger shoes and/or more aggressive friction material to meet the NHTSA standard, Hicks says air disc brakes have been exceeding those stopping distance requirements for many years. "We're at a point now where both disc and drum brakes meet the mandate very comfortably, but it was never really a problem for disc brakes," adds Dennis Griffi n, product manager, commercial vehicle friction at Abex, a Federal-Mogul Motorparts brand. Disc brakes also operate much quieter — partially because they didn't require such wholesale changes to remain vi- able under RSD regulations, says Keith McComsey, director of marketing and customer solutions, wheel end at Bendix Spicer Foundation Brake. "For manufacturers to meet the RSD requirements for drum brakes they had to be much more aggressive [with their friction material] and that aggressiveness has created brake noise," he says. "Air disc brakes don't have that." And if that's not enough, disc brakes also offer benefi ts in the service bay, with both longer life cycles for replacement parts (brake pads and rotors) and easier service procedures. "Some people believe when they go to air disc brakes that they won't have [to do] maintenance anymore. That's not true," says Chappell. "The maintenance is less common but it's still required." McComsey notes that with longer air disc brake pad life, a fl eet turning over new trucks every 3 to 4 years "might not even need to touch replacement pads," and that wearable components on an air disc brake tend to last "anywhere from 1.5 to 2 times the life" of comparable drum brake parts. Fortunately it's a pretty easy repair, Chappell says. "Basically you just remove the wheel, and in our case we have a boltless pad retention method. So you take the old pads out and put in new ones and away you go," he says. "It takes less than half the time" as a drum brake shoe replacement, Urban adds. Hicks agrees, and says even techni- cians previously unfamiliar with disc brakes can usually master the routine in just a few tries. 16 Cover Story T R U C K P A R T S & S E R V I C E | A u g u s t 2 0 1 6 almost in the inverse, clamping friction- Status quo in the automotive industry SAF-Holland introduced its new P89 and P89 Plus air disc brakes in North America in June. To meet the RSD requirements for drum brakes [manufacturers] had to be much more aggressive [with their friction material] and that aggressiveness has created brake noise. Air disc brakes don't have that. – Keith McComsey, director of marketing and customer solutions, wheel end at Bendix Spicer Foundation Brake