Technical Paper
Brake Performance Testing and Truck Runaway Analysis
2003-11-10
2003-01-3396
Commercial vehicle air brake systems are associated with more heat problems than hydraulic brake systems on passenger vehicles. A typical commercial vehicle runaway involves a driver who has lost the ability to control the speed of his vehicle and runs off the road because of too much speed in a curve or collides with slower moving vehicles. In some cases the driver has the ability to control speed to some extent and is unaware that he has overused the brakes until faced with a situation requiring a heavy brake application. The loss of braking capacity on long steep downgrades is due to the combined effects of heating, brake system design, friction material properties, maintenance, and brake adjustment. Brake drums expand as temperatures increase causing the strokes of the pushrods to increase. Brakes that are out of adjustment or at the limit of adjustment before heating can lose effectiveness with less heating than properly adjusted brakes.