CDL Doubles and Triples Practice Test 1
What is rearward amplification?
"Crack-the-whip" effect when making quick lane changes. Rearward amplification is increased in doubles and triples. A conventional double has a rearward amplification of 2.0, which means that it is twice as likely to turn over as a standard 5 axle trailer. A triple has a rearward amplification of 3.5.
In a set of triples, where should the heaviest trailer be?
First trailer position (behind the tractor). The lightest trailer should be in the third/last position. Putting the heaviest trailer in the first position behind the trailer will provide the safest handling on the road.
Why should you never disconnect the pintle hook with the dolly still under the rear trailer?
The dolly tow bar may fly up, possibly causing injury. If you unlock the pintle hook with the dolly still under the rear trailer, it will also be very difficult to re-couple.
When connecting the converter dolly to the front trailer, what do you do first?
Back first semitrailer in front of dolly tongue. The steps to connect the converter dolly to the front trailer are: back first semitrailer into position in front of dolly tongue; hook dolly to front trailer; lock pintle hook; secure converter gear support in raised position.
If a second trailer does not have spring brakes, how should you set the brakes when you are coupling?
Drive the tractor close to the trailer, connect the emergency line to charge the trailer air tank and disconnect the emergency line. This process will set the trailer emergency brakes (assuming that the slack adjusters are correctly adjusted). You can also chock the wheels as an additional measure.
Pushing in the trailer air supply knob will do what?
Supply air to the emergency air line. The trailer air supply control knob is used to control the tractor protection valve. You push the knob in to supply the trailer with air (via the emergency air line) and pull it out to shut off the air and put on the trailer emergency brakes.
How should you check that you have sufficient emergency airflow to all trailers in a set of doubles or triples?
Push in the red trailer air supply knob, open the emergency line shut-off valve at the rear of the last trailer and listen for air escaping. To check the service line air flow, you use the trailer hand brake to supply air to the service lines. Go to the rear of the last trailer, open the service line valve and listen for air escaping.
What is the main purpose of a trailer shut-off valve?
To close the air lines of the last trailer to prevent air from leaking out. Shut-off valves (sometimes referred to as cut-out cocks) are located at the back of trailers used to tow other trailers. These valves allow you to close of the air lines when other trailers are not being towed. Trailer hand valves (also called trolley valves or Johnson bar) work the trailer brakes. The trailer air supply control controls the trailer emergency brakes.
What is the correct position of the shut-off valves for the last trailer of a doubles or triples set?
Fully closed. Shut-off valves (sometimes referred to as cut-out cocks) are located at the back of trailers used to tow other trailers. All valves should be in the open position except on the last trailer which should be in the closed position.
What is the correct position of the shut-off valves for the first trailer of a doubles or triples set?
Fully open. Shut-off valves (sometimes referred to as cut-out cocks) are located at the back of trailers used to tow other trailers. All valves should be in the open position except on the last trailer which should be in the closed position.
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