Inspecting Air Brake Systems
A proper inspection catches problems before they become emergencies. Begin with a walk-around: check for leaks, damaged hoses, cracked lines, and loose fittings. Look at the slack adjusters; with the brakes released, the angle between the pushrod and slack adjuster should be about 90 degrees. Check that the pushrods move freely and return.
Drain the reservoirs to remove moisture and check for contamination. Then build pressure and listen for leaks. With the engine running, the compressor should build pressure to the governor cut-out level. Watch the gauges: pressure should rise steadily, and the low pressure warning should function when pressure is low.
Inspect the brake chambers for damage, and check that the spring brakes apply and release properly. Test the parking brake and confirm it holds the vehicle. Look at the tires and wheels for obvious problems, and check that the brake lights work.
Traps in exam questions include confusing the 90-degree slack adjuster angle with other measurements, or forgetting that inspections should be done with the brakes released for the slack adjuster check. Another trap is skipping the reservoir drain, which is essential for removing moisture that can freeze or corrode the system.
Rule of thumb: inspect, drain, build pressure, listen for leaks, and test the warning system and spring brakes before every trip.