Better stopping power is probably the most oft-touted advantage of air disc brakes, but advanced drum brakes easily meet the requirements, too. However, when you look at the reduced and simplified maintenance requirements of ADBs, better stopping power becomes the icing on the cake.

In a typical longhaul application, fleet technicians may never need to put a wrench to an ADB over the life of a tractor. A trailer, sure, but they tend to be kept a little longer and run fewer miles annually. With rotor life in the 700,000-mile range and pads going out to 400,000 and more, for many fleets, the right ADB spec could put an end to regular brake maintenance other than inspections.

“The normal maintenance cycle for disc brakes is not quite double that of drum brakes in a typical application,” says Gopi Krishnan, Meritor’s director of brakes for North America. “The pads in a disc brake system should go out to 500,000 or 600,000 miles. The rotors can be expected to last up to 1 million miles. As long as you don’t have to change the rotors, you will most likely see lower maintenance costs and therefore lower overall cost of ownership.”

Krishnan notes that the routine service of drum brakes, such as a reline, can take an hour or more per wheel-end.

“A pad change on a disc system can take as little as 20 minutes, in some cases without removing the wheel,” he says, “Rotor or drum changes can both be somewhat more complicated, but it’s likely that the first owner of the truck would never need to change a rotor.”

In fact, aside from a pad change, most disc brake systems in linehaul fleets following typical fleet trade-in cycles would likely be traded in without ever requiring any serious brake maintenance.

The same could be said for the premium drum brake installations, but there are other parts to such systems that do require periodic inspection. Brake adjusters need periodic lubrication, clevis pins need to be checked for free movement and linings and drums need to be inspected for cracking, expansion of the linings, oil contamination, etc. And of course proper brake stroke length need to be checked regularly, as even automatic brake adjusters don’t guarantee the brakes will not go out of adjustment.

All that is almost eliminated with ADBs. 

One fleet we spoke with had seen some water intrusion around the piston seals on the calipers, which prompted them to increase the frequency of their ADB inspections and to consider replacing the seals at certain intervals. Apparently ADBs are not totally trouble-free, but they are certainly less of a maintenance burden than traditional drum brakes.

Drum brakes, as reliable as they are, are still regularly put out of service at rates approaching 20%. Most of the OOS events are adjustment-related. With disc brakes, that problem basically disappears.

“Today there is not a good way to do a roadside inspection of a disc brake, although that could change in the future,” says Gary Ganaway, director of Original Equipment & Technical Sales at Bendix Commercial Vehicle Systems. “The disc brake adjustment mechanism is internal to the brake, and not as susceptible to manual adjustment. Provided the caliper is working as prescribed, there’s not much risk of a failed brake inspection.”

Which means fewer chances for dings on a fleet’s score under the U.S. DOT’s Compliance, Safety and Accountability (CSA) program.

Severe Service Improves ROI

Even for fleets that keep trucks longer, simplicity of service and inspection and a significant reduction in downtime helps build the maintenance case for ADBs, especially in applications where brakes are chewed up quickly, like refuse and city P&D.

“Disc brake repairs are significantly faster than drum brake repairs,” notes Tony Ryan, technical services and training manager for SAF-Holland. “And disc pad reline takes only a few minutes per wheel to complete once the wheels are off.”

Routine brake inspections and minor service events also can be completed in less time than with drum brakes, further building the ROI case.

“There is significantly less maintenance on disc brakes when compared to drum brakes because there are fewer components.” Ryan says. “In addition, there are no grease points on the caliper and no chamber strokes to measure on air disc brakes, simplifying DOT inspections.”

In less severe but longer-life applications, like the 10-year trailers used in longhaul service, maintenance costs can be the tipping point in the ROI calculation says John Thomson, North American sales manager at TMD friction.

“Look at the servicing costs and lining change costs both in terms of costs as well as the time it takes to change them,” he says. “On long-life vehicles like trailers you could look at saving multiple brake changes during the life of the vehicle.”

That’s certainly something to consider when doing the ROI on ADB. And don’t forget the downtime savings or the fact that you might never get another citation for brake adjustment.