Over the past several years, adoption of air disc brakes (ADBs) has climbed to 18% to 25% of brakes ordered on trucks, according to brake manufacturers, who anticipate that number reaching 50% within the next decade. This means that technicians will need to be familiar with both the tried-and-true drum brakes and their disc brake counterparts.
One of the major advantages of air disc brakes is the extended service interval for brake friction. However, that does not mean that preventative maintenance schedules are also extended.
“Any brake system requires preventative maintenance not only to keep it operating effectively in providing continuous brake performance, but also to provide long life to the components. Air disc brakes are no different,” says Keith McComsey, director of marketing and customer solutions, wheel-end, with Bendix Spicer Foundation Brake.
McComsey recommends the following preventative maintenance steps:
- Inspect pad friction thickness to ensure that it has not fallen below the minimum, verifying even pad wear not only across the pad but also comparing the inboard vs. outboard pad, and making sure that friction is not cracked.
- Verify that rotor thickness is greater than the minimum and also make sure that there are no stress cracks in the rotor. If stress cracks are present, check them against acceptable levels.
- Make sure that your boots are in good working order and do not exhibit any tearing of the boot material that would allow moisture and contaminants into the caliper.
- Verify that the caliper can slide freely.
Jon Morrison, president of WABCO Americas, also emphasizes the importance of getting on a schedule to ensure properly installed and maintained ADBs on commercial vehicles. Morrison shares a few stats to back him up: Brake violations, including brake adjustments and brake system violations, accounted for 41.4% of all out-of-service vehicle violations, according to the Commercial Vehicle Safety Alliance’s 2017 International Roadcheck results. Out-of-adjustment brake concerns alone accounted for 26.9% of all vehicle out-of-service violations. Clearly, this is important to address.
Morrison recommends visually inspecting or measuring the brake pad thickness with wheels on every six months, and doing the same with the wheels off every 12 months.
“Adhering to a maintenance schedule helps early detection of required maintenance, avoiding more extensive brake damage, thereby reducing downtime, and improves overall vehicle safety,” Morrison says. “Preventative brake upkeep also enhances the overall life of the braking system by reducing the need to replace rotors or other hard parts in cases where the brakes were not maintained. This, in turn, reduces overhead.”
Greg Cooper, a product manager for Stemco and an ASE certified brake technician, advises technicians to pay close attention to any torn dust boots, heavily corroded abutment features or slides that are erratic. If the caliper has restricted movement back and forth, then the brake system is not set to its correct design position and can result in premature failure. Also, a close inspection of the tappets, or pistons for damage, will ensure proper pad pressure distribution and actuation of the braking features.