ABS And Brake Imbalance

While antilock braking systems have improved safety in many ways, they also make it more difficult to identify a brake imbalance situation. Wet or icy roads are not the only things that can cause a wheel lockup. So can overworked brakes.

Before ABS, an attentive driver could feel the effects of wheel lockup on dry pavement and smell overworked brakes. But because the ABS keeps the wheel from locking up, effects of imbalanced brakes are masked from the driver or mechanic.

"ABS was never designed to be used on routine stops," says John Hawker, service engineer with Bendix Spicer Foundation Brake. "ABS should only come into play in a true panic stop."

Hawker uses the information from the ABS to help diagnose brake imbalance. When consulting with fleets, he downloads the information from the ECU on ABS events – documenting how frequently the antilock brake system is activated to prevent wheel lock-up.

"After the first brake job, I see repeated ABS events, because we lost that matching balance," he says. "One or two axles are doing all the work, and you're getting close to a wheel lockup and firing off the ABS."

Armed with that information, he can sit down with a director of maintenance and show him how the trailer brakes are out of balance with the tractor and causing excessive wear on the drive axle. Or perhaps the steer axle brakes are wearing out prematurely because there's the wrong type of friction on the drives.