Missouri CDL — Air Brakes Practice Test 8

1.What is a 'wig wag' device?

A gauge that shows how much pressure is appliedA valve that drains the tanks automaticallyA backup buzzer wired to the stop lightsA mechanical arm that drops into the driver's view when pressure sinks below 55 psi

2.How do you check that the parking brake will hold?

Rev the engine to redline with the brake offCoast downhill without the parking brakePress the brake pedal while parkedSet the parking brake and gently try to pull forward in a low gear

3.Why is it a mistake to pump the brake pedal on and off without need?

It overheats the slack adjustersIt forces the governor to cut out earlyIt drains oil out of the compressorIt can release air faster than the compressor replaces it, dropping pressure too low to brake

4.How do spring brakes hold the vehicle when the air pressure is lost?

A backup compressor keeps them chargedHydraulic pressure takes over automaticallyPowerful springs, held off by air while driving, clamp the brakes once the air is goneA parking pawl locks the transmission

5.Why is draining the air tanks important?

Water and oil collect inside and, if frozen, can cause the brakes to failOld air must escape so fresh air compresses betterIt lightens the load the compressor has to liftIt resets the governor to its cut-in pressure

6.When you pull on an s-cam slack adjuster by hand, about how much movement suggests it needs adjustment?

Any movement at allMore than three inchesMore than roughly one inch where the push rod attachesOnly if it does not move

7.How do air-operated disc brakes clamp the rotor rather than using an s-cam?

A wedge is driven between two shoesA hydraulic piston fed from a master cylinder pushes the padsAn electric solenoid clamps each wheelA power screw turned by the slack adjuster squeezes the disc between caliper pads

8.An air brake arrangement is really a combination of three braking functions. Which set correctly names them?

The service, parking, and emergency brakesThe hydraulic, mechanical, and vacuum brakesThe front, rear, and trailer brakesThe primary, secondary, and reserve brakes

9.At about what pressure do a tractor or straight truck's spring brakes fully engage on their own?

55 to 75 psi100 to 125 psi80 to 90 psi20 to 45 psi

10.What best describes a dual air brake system?

One system driven by two compressorsA system that switches between air and hydraulicA single system with two governors and one tankTwo separate air brake systems operated by a single set of controls