An investment in air disc brakes pays off in several ways both on the road and in the shop, from shorter stopping distances to reduced maintenance time. This Bendix Tech Tip addresses actions that fleets and owner-operators can take to protect that investment and extend the life of their air disc brake (ADB) pads and rotors.
“The more people realize the benefits of air disc brakes, the more we want to help them maximize ADB advantages over the life of the brake, to really get the most out of their investment in the technology,” said Mark Holley, Bendix director of marketing and customer solutions, Wheel-End. “The good news is that taking care of ADBs to ensure they reach their full potential is a pretty straightforward matter of knowing some basic facts, paying attention to your brakes, and making good choices when it comes to replacement parts.”
Considering the couple
An understanding of the pairing of the brake pads and rotor – the friction couple – is a good place to begin, according to Holley.
“In technical terms, the friction couple converts the kinetic energy of the spinning rotor into heat energy by clamping the pads against the rotor, slowing the wheel-end,” he said. “The contact between the pad and rotor creates friction, generating heat energy that the rotor stores and then dissipates. In fact, one of the reasons ADBs don’t experience brake fade is that their design allows for much quicker heat dissipation than drum brakes.”
The best friction couples result when rotors and pads are designed and engineered specifically for each other. This is because there are many complex variables that determine how these components will perform when they come together to stop a vehicle, from the physical design and metallurgy of a rotor to the proprietary friction material in a brake pad.
“When an OE like Bendix can determine exactly what goes into both the rotor and brake pad individually, it means we can engineer them to optimize torque output – the actual stopping force provided to slow the wheel-end – and wear optimally together,” Holley explained. “We can design specific pads to wear at a rate with some equivalence to the rotor. This protects rotor life and helps ensure a quality friction couple. The wrong pad, for instance, may last longer but wear out the rotor faster.”
Know the friction
As ADBs have gained market acceptance, pad friction has evolved to account for varying fleet factors, including application, tractor/trailer brake combinations, and duty cycle. Not all aftermarket friction will meet FMVSS-121 requirements in effect at the time of a vehicle’s manufacture – and some pads have been shown to increase stopping distances when compared to OEM friction. When replacing ADB pads, Bendix recommends that fleets and owner-operators use like-for-like components to maintain the original manufacturer’s braking performance levels.
Bendix has created frictions to meet several wear rate performance needs, from managing high temperatures in applications with repeated, frequent brake usage such as refuse, school bus, and pickup/delivery to longer life friction for line-haul and trailers through more wearable volume.
