Wisconsin CDL — Air Brakes Practice Test 1

1.When may you fully apply the brakes during an emergency stop?

Whenever the road is wetOnly when the trailer is emptyWhen you always drive a vehicle with working ABS on all axlesOnly at speeds below 20 mph

2.An automatic front wheel limiting valve sends full air to the front brakes under what condition?

When the brakes are applied hard, at about 60 psi or moreOnly when the driver moves the cab control to 'slippery'Whenever the parking brake is releasedOnly at speeds below 20 mph

3.How do you test that the parking brake will actually hold?

Set it, then gently try to pull forward in a low gearRev the engine to full throttle in neutralPress the brake pedal as hard as you canLet the vehicle roll backward down a slight hill

4.What must you always do before leaving your vehicle unattended?

Set the parking brakes or chock the wheelsDrain the air tanks completelyLeave it in a low gear with the brakes offSwitch on the four-way flashers

5.At about what tank pressure does the governor let the compressor begin pumping again?

Around 150 psiAround 100 psi, the cut-in levelAround 45 psiAround 20 psi

6.When the low air pressure warning first activates, what is the correct action?

Keep driving until the spring brakes set themselvesPump the pedal to rebuild pressure fastGet the vehicle safely stopped immediately, while the service brakes still respondRelease the parking brake control to reset the system

7.Only the tractor of your combination has ABS, and the trailer starts to swing out while you are braking hard. What should you do?

Ease up on the pedal when it is safe to, until the trailer falls back into linePush the pedal down harder so the trailer brakes drag it backApply the trailer hand valve fully and steer toward the shoulderPull the parking brake knob out to straighten the rig

8.What is a dual air brake system?

One air system feeding two separate pedalsA system that switches between air and hydraulic brakingTwo compressors that share a single air tankTwo separate air brake systems run by one set of controls

9.What is the main function of an antilock braking system (ABS)?

It shortens every stop by a set distanceIt keeps the wheels from locking up during hard brakingIt replaces the need for spring brakesIt drains the air tanks automatically

10.Why is it important to empty the air storage tanks?

To lower the pressure so the brakes release fasterTo let fresh air replace stale air in the linesTo keep the alcohol evaporator from overfillingWater and oil collect inside, and the water can freeze and cause brake failure