Tech Tip: How often to inspect air disc brakes

Myth: Air disc brakes need to be inspected only once yearly

Fact: Air disc brakes (ADB) should be inspected at every preventive maintenance (PM) inspection.

“Among their benefits, air disc brakes (ADB) have extended service intervals for friction or rotor replacement when compared to drum brakes, but this does not mean that ADB maintenance intervals get extended too,” said Keith McComsey, Bendix Spicer Foundation Brake (BSFB) director of marketing and customer solutions. “Inspecting at every preventive maintenance inspection is still required to make sure everything is in good working order – it’s this regular activity that contributes to the brake’s longevity. Most of these PM inspections do not even require removal of the wheel, making it a quick, easy process.”

One of the key inspections for air disc brakes is a visual check of caliper movement to ensure that it slides freely, according to Kevin Pfost, BSFB product specialist and longtime master technician. Visual inspection of the rotor is also key. Look for rotor surface cracks (due to heat stress) that exceed allowable limits. To get the best view of the rotor from outside to inside, use an inspection mirror.

Use the mirror to check pad wear as well. Minimum allowable friction material thickness is 2 mm. For a better view, use a Wi-Fi borescope camera, found at many retail outlets, including home supply stores.

Also during inspection, check the mounting hardware of calipers and air chambers – loose mounting bolts mean an out-of-service (OOS) brake. Make sure the guide pin covers are not missing, and ensure proper running clearances between the rotor and pads.

“A wheel-off inspection becomes necessary if you see something wrong during the visual check,” Pfost said. “For example, if the caliper does not move freely, or if you see a crack in the rotor. During inspection, if you see the pads are wearing unequally from inboard pad to the outboard pad – by a noticeable amount – then you would remove the wheels and do a deeper dive inspection. At this time you should also take the time to look for damaged tappets and guide pin boots. It’s the regular routine checks that act as the early warning for issues requiring immediate attention, while helping protect the life of the ADB’s components.”