Doubles and Triples CDL Practice Test

1. To uncouple a converter dolly, apply the converter gear spring brakes or chock the wheels, then __________

• A. release the pintle hook on the first semitrailer.
• B. slowly pull clear of the dolly.
• C. lower the dolly landing gear.
• D. disconnect the safety chains.

Explanation:
To uncouple twin trailers, uncouple the converter dolly after uncoupling the rear trailer. Lower the dolly landing gear. Disconnect the safety chains. Apply the converter gear spring brakes or chock the wheels. Release the pintle hook on the first semi-trailer. Slowly pull clear of the dolly. Never unlock the pintle hook with the dolly still under the rear trailer. The dolly tow bar may fly up, possibly causing injury, and making it very difficult to re-couple.

In the handbook:
7.2.2: Coupling and Uncoupling - Uncoupling Twin Trailers

2. To connect a converter dolly to the rear trailer when coupling twin trailers, open the shut-off valves at the rear of the first trailer (and on the dolly if so equipped), then __________

• A. raise the landing gear completely.
• B. charge the trailers (push in the "air supply" knob) and check for air at the rear of the second trailer by opening the emergency line shut-off.
• C. connect the safety chains, air hoses, and light cords.
• D. none of the above

Explanation:
To connect a converter dolly to the rear trailer when coupling twin trailers, first make sure the trailer brakes are locked and/or wheels are chocked. Make sure the trailer height is correct. (It must be slightly lower than the center of the fifth wheel, so the trailer is raised slightly when the dolly is pushed under.) Back the converter dolly under the rear trailer. Raise the landing gear slightly off the ground to prevent damage if the trailer moves. Test the coupling by pulling against the pin of the second semitrailer. Make a visual check of the coupling. (There should be no space between the upper and lower fifth wheel. The locking jaws should be closed on the kingpin.) Connect the safety chains, air hoses, and light cords. Close the converter dolly air tank petcock and shut-off valves at the rear of the second trailer (service and emergency shut-offs). Open the shut-off valves at the rear of the first trailer (and on the dolly if so equipped). Raise the landing gear completely. Charge the trailers (push the "air supply" knob in) and check for air at the rear of the second trailer by opening the emergency line shut-off. If air pressure isn't there, something is wrong and the brakes won't work.

In the handbook:
7.2.1: Coupling and Uncoupling - Coupling Twin Trailers

3. To use a tractor and first semitrailer combination to pick up a converter dolly, pull the dolly into position as close as possible to the nose of the second semitrailer, then __________

• A. wheel the dolly into position in front of the second trailer in line with the kingpin.
• B. unhook the dolly from the first trailer.
• C. lower the dolly support.
• D. none of the above

Explanation:
To use the tractor and first semitrailer combination to pick up the converter dolly when coupling twin trailers, position the combination as close as possible to the converter dolly. Move the dolly to the rear of the first semitrailer and couple it to the trailer. Lock the pintle hook. Secure the dolly support in the raised position. Pull the dolly into position as close as possible to the nose of the second semitrailer. Lower the dolly support. Unhook the dolly from the first trailer. Wheel the dolly into position in front of the second trailer in line with the kingpin.

In the handbook:
7.2.1: Coupling and Uncoupling - Coupling Twin Trailers

4. Supply air to the service line during the pre-trip inspection with the __________

• A. trailer air supply knob.
• B. trailer hand brake.
• C. emergency line shut-off valve.
• D. none of the above

Explanation:
Check the brakes on a double or triple trailer as you would any combination vehicle. You must make additional checks on your double or triple trailers. To check that air flows to all trailers (double and triple trailers) during your pre-trip inspection, use the tractor parking brake and/or chock the wheels to hold the vehicle. Wait for the air pressure to reach normal, then push in the red "trailer air supply" knob. This will supply air to the emergency (supply) lines. Use the trailer handbrake to provide air to the service line. Go to the rear of the rig. Open the emergency line shut-off valve at the rear of the last trailer. You should hear air escaping, showing the entire system is charged. Close the emergency line valve. Open the service line valve to check that service pressure goes through all the trailers (this test assumes that the trailer handbrake or the service brake pedal is on), and then close the valve. If you do NOT hear air escaping from both lines, check that the shut-off valves on the trailer(s) and dolly(ies) are in the OPEN position. You MUST have air all the way to the back for all the brakes to work.

In the handbook:
7.4.1: Doubles/Triples Air Brake Check - Additional Air Brake Checks

5. To uncouple a converter dolly, lower the dolly landing gear, then __________

• A. release the pintle hook on the first semitrailer.
• B. slowly pull clear of the dolly.
• C. apply the converter gear spring brakes or chock the wheels.
• D. disconnect the safety chains.

Explanation:
To uncouple twin trailers, uncouple the converter dolly after uncoupling the rear trailer. Lower the dolly landing gear. Disconnect the safety chains. Apply the converter gear spring brakes or chock the wheels. Release the pintle hook on the first semi-trailer. Slowly pull clear of the dolly. Never unlock the pintle hook with the dolly still under the rear trailer. The dolly tow bar may fly up, possibly causing injury, and making it very difficult to re-couple.

In the handbook:
7.2.2: Coupling and Uncoupling - Uncoupling Twin Trailers