North Carolina CDL — Air Brakes Practice Test 9

11.When the low-air warning first lights up while driving, what should you do?

Keep going and pump the pedal to rebuild pressureCome to a controlled, safe stop immediately, before you lose the ability to brakeWait for the spring brakes to stop the vehicle automaticallyRelease the parking brake control to add air

12.Why should you avoid pressing the brake pedal while the spring brakes are applied?

The combined spring and air forces could damage the brakesIt will drain the trailer's air tank instantlyIt disables the ABS warning lampIt forces the governor to cut out early

13.With the engine off and the foot brake fully applied for one minute, the air-loss rate is too high on a single vehicle if pressure drops more than:

3 psi in one minute10 psi in one minute1 psi in one minute20 psi in one minute

14.Compared with hydraulic brakes, air brakes add 'brake lag.' What is brake lag?

The time it takes the compressor to refill the tanksThe delay before the ABS activatesThe short time for air to travel the lines and the brakes to act after you press the pedalThe distance you drift before noticing a hazard

15.On a vehicle equipped with dual air brakes, how much pressure should build in each circuit before you begin driving?

60 psi150 psi45 psi100 psi

16.When inspecting brake drums, how large a crack is still within limits?

Any crack means the drum passesUp to the full width of the friction areaUp to one-quarter the width of the friction areaNo longer than half the width of the friction area

17.At about what tank pressure does the governor normally reach its 'cut-out' point and stop the compressor?

Around 100 psiAround 125 psiAround 60 psiAround 150 psi

18.If your tanks have manually operated drain valves rather than automatic ones, how often should you drain them?

Once a weekAt the end of each driving dayOnly when the low-air warning soundsAbout every 5,000 miles

19.Why is repeatedly pumping (fanning) the brake pedal when it isn't needed a bad habit in an air-brake vehicle?

It overheats the alcohol evaporatorIt forces the governor into an early cut-outIt can release air faster than the compressor can replace it, dropping pressure too lowIt permanently locks the spring brakes

20.On a long, steep downgrade, the manual describes the use of the brakes as:

The main way to control speed, with the engine playing no partUnnecessary if you are already in a high gearSafe only if you hold them applied continuouslyA backup to the engine's own braking, applied only after you have shifted into a low gear