Air disc brakes are a logical choice

One of the major items that carriers receive violations on is brake adjustment. Air disc brakes (ADB) have an internal adjuster, which is not subject to the same environmental elements as an external slack adjuster, resulting in trouble-free operation.

According to the Commercial Vehicle safety Alliance’s Roadcheck 2013 ( that took place June 4 to 6, 49.6 percent of the Out-of-Service violations were related to brake adjustment and other brake system violations.

With an improved design, air disc brakes eliminate the need for an external automatic slack adjuster. The adjustment mechanism for ADB is sealed for the life of the caliper, almost eliminating the possibility of a violation for out-of-adjustment brakes.

Brake Life

Along with taking less time to do a brake job, the interval in between brake jobs for disc brakes is much longer and can be up to double the life of a drum brake. The design of an air disc brake makes the brake application more efficient over the course of a lining life.

There are two key differences which lead to longer lining life for air disc brakes: advanced lining material and more robust friction surfaces. These superior materials cannot be utilized in a drum brake because the surfaces are curved and the material is too brittle to be molded into that shape.

On a disc brake, the pad and friction surface are flat, ensuring even and consistent contact.

A disc brake also has more efficient cooling than a drum brake and the friction surfaces are exposed to the ambient air. In combination, this promotes longer lining life.

Robert Maschmeier of Bob’s Moraine Trucking — a Franklin, Ohio-based carrier of concrete related products ( — said it best: “The disc pads from our WABCO air disc brake tractors last longer than the best brake linings of our drum brake tractors.”

This increased service interval time, plus the reduced time to change the pads, means huge savings for a fleet’s yearly brake maintenance costs.

A Key Component

The adjusting mechanism is one of the key components in a brake. Most air disc brakes are a dual piston design.

WABCO has developed a simple yet robust single-piston design that avoids the need for special synchronizing of the pistons. This design greatly reduces the moving parts count of the caliper when compared to dual piston disc brakes, thus ensuring efficient and reliable operation over the life of the brake.

Brake Performance

With the final introduction of the last phase of the new federal reduced stopping distance regulations this year, many commercial vehicle manufacturers have had to increase the performance of their brakes, especially on the front axle.

Air disc brakes are a logical choice to provide that improved stopping power. Due to the design of a disc brake, the performance is more stable and balanced across the full range of operating conditions, from light braking to an emergency stop.

Disc brakes come into their own under difficult conditions. This is especially true when braking on prolonged down hill grades or when stopping from high speed. There is little or no brake fade felt by the driver and the vehicle feels stable and secure.

Track Record

One misconception about air disc brakes is that they are unproven.

WABCO air disc brakes have been available for more than 30 years and are used worldwide in truck, bus and trailer applications with over three million brakes in service.

WABCO air disc brakes are available on Freightliner and Western Star models, as well as major trailer axle manufacturers.

In today’s challenging operating environment, where a fleet has to balance the running costs of its fleet and ensure a safe environment for its drivers, air disc brakes are a logical choice.

Steve Hampson is director of sales for WABCO North America. WABCO is a leading global supplier of technologies and control systems for the safety and efficiency of commercial vehicles. Founded nearly 150 years ago, WABCO continues to pioneer breakthrough electronic, mechanical and mechatronic technologies for braking, stability and transmission automation systems supplied to the world’s leading commercial truck, bus and trailer manufacturers.