CDL Doubles/Triples (T) Endorsement Test
Air brake checks: practice questions
Our CDL Doubles/Triples bank has 21 questions on this topic. Here are 5 of them with answers; the full mock exam draws from every topic, like the real one.
Question 1
What does the service line carry to the trailers?
- Air that keeps the spring brakes released while you drive
- Air for the trailer suspension only
- Air controlled by the foot brake or trailer hand brake
- Electric power for the ABS
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C. Air controlled by the foot brake or trailer hand brake — The service line carries air controlled by the foot brake or the trailer hand brake (CDL Manual 6.2.4)
Question 2
Before checking that air flows to all trailers, how do you hold the rig in place?
- With the trailer hand valve only
- By leaving it in gear with the engine shut off
- By lowering all the landing gear
- With the tractor parking brake and/or wheel chocks
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D. With the tractor parking brake and/or wheel chocks — Use the tractor parking brake and/or chock the wheels to hold the vehicle (CDL Manual 7.4.1)
Question 3
Where do you open the emergency line shut-off valve to check air flow?
- On the tractor dash
- At the rear of the first trailer
- At the front of the dolly
- At the rear of the last trailer
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D. At the rear of the last trailer — Go to the rear of the rig. Open the emergency line shut-off valve at the rear of the last trailer (CDL Manual 7.4.1)
Question 4
How do you test the tractor protection valve?
- Open all trailer drain valves at once
- Disconnect the service line while driving
- Pull the red knob out with the engine running
- Charge the system, shut off the engine and pump the brake pedal to lower the pressure
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D. Charge the system, shut off the engine and pump the brake pedal to lower the pressure — Charge the trailer air brake system, shut the engine off, step on and off the brake pedal several times to reduce the air pressure in the tanks (CDL Manual 7.4.1)
Question 5
When testing the tractor protection valve, what should the trailer air supply control do as pressure falls?
- Release the trailer brakes
- Pop out, or go from normal to emergency
- Light up green
- Stay pushed in until the pressure reaches zero
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B. Pop out, or go from normal to emergency — The trailer air supply control should pop out (or go from normal to emergency position) when the air pressure falls into the pressure range specified by the manufacturer (CDL Manual 7.4.1)