TMD Friction asked its engineers to find out if disc and drum brakes are compatible and whether they will work properly with each other. “The short answer is yes—to a certain degree,” reports John Thompson, OEM sales manager for TMD Friction.

“Engineers calculated the brake force required for a mountain descent of 7.5% grade for 8 miles,” Thompson explains. “It was a worst-case calculation that did not include retarders, which should always be used in the real world for long descents. Once brake force and time to travel the distance at 35 MPH were figured out, a dynamometer test was run, dragging the brake at the desired torque to maintain the vehicle speed. The procedure was run for both a disc and a cam brake.

“The two brakes were coupled mathematically, so the required torque was maintained throughout the mountain descent,” he continues. “The result was the brakes worked well together up to around 650°F. After that, the disc brakes did most of the work. The conclusion: For normal operations and temperature ranges, disc and drum brakes are compatible; for more severe applications, make sure retarders are used to dissipate some of the energy. Keep temperatures low and all brakes well-maintained, and the combination will serve you well.”