CDL Section 7: Doubles and Triples

Questions and Answers

What is a converter dolly?

It is a coupling device of one or two axles and a fifth wheel by which a semitrailer can be coupled to the rear of a tractor-trailer combination forming a double bottom rig.

Do converter dollies have spring brakes?

True

What three methods can you use to secure a second trailer before coupling?

Connect the emergency line, charge the trailer air tank, and disconnect the emergency line. 2) Spring brakes. 3) Wheel chocks.

How do you check to make sure trailer height is correct before coupling?

It must be slightly lower than the center of the fifth wheel, so the trailer is raised slightly when the dolly is pushed under. Signup and view all the answers

What do you check when making a visual check of coupling?

No space between upper and lower fifth wheel. Locking jaws closed on kingpin. Signup and view all the answers

Why should you pull a dolly out from under a trailer before you disconnect it from the trailer in front?

The dolly tow bar may fly up, possibly causing injury, and making it very difficult to re-couple. Signup and view all the answers

What should you check for when inspecting the converter dolly?

<ol> <li>If spare tire is carried on converter gear (dolly), make sure it's secured. 2) Pintle hook is latched.</li> </ol> Signup and view all the answers

Should the shut-off valves on the rear of the last trailer be ______? On the first trailer in a set of doubles? On the middle trailer of a set of triples?

Closed; Open; Open. Signup and view all the answers

How can you test that air flows to all trailers?

Wait for 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 shutoff valve at the rear of the last trailer. You should hear air escaping, showing the entire system is charged. Signup and view all the answers

How do you know if your converter dolly is equipped with antilock brakes?

Dollies manufactured on or after March 1, 1998, are required to have a lamp on the left side. Signup and view all the answers

Study Notes

Converter Dolly and Coupling

A converter dolly is a coupling device with one or two axles and a fifth wheel that connects a semitrailer to a tractor-trailer, forming a double bottom rig.
Converter dollies are equipped with spring brakes, ensuring safety during operation.

Securing Second Trailer

Three methods to secure a second trailer before coupling include:
- Connecting the emergency line, charging the trailer air tank, and then disconnecting the emergency line.
- Engaging spring brakes.
- Utilizing wheel chocks.

Trailer Height Check

Before coupling, the trailer height must be slightly lower than the center of the fifth wheel, allowing it to raise slightly when the dolly is pushed underneath.

Coupling Visual Inspection

During a visual check of the coupling:
- Ensure there is no space between the upper and lower fifth wheel.
- Confirm that the locking jaws are closed around the kingpin.

Safety Precautions

It's essential to pull a dolly out from under a trailer before disconnecting it from the trailer in front to prevent the dolly tow bar from flying up, which can cause injury and complicate re-coupling.

Converter Dolly Inspection

When inspecting the converter dolly:
- Ensure the spare tire, if carried, is secured.
- Check that the pintle hook is latched.

Shut-off Valve Positions

The shut-off valves on the last trailer in a set of doubles should be closed, while those on the first trailer must be open. In a set of triples, the shut-off valves on the middle trailer should also be open.

Air Flow Testing

To test that air flows to all trailers, follow these steps:
- Wait for normal air pressure.
- Push in the red "trailer air supply" knob to supply air to the emergency (supply) lines.
- Use the trailer handbrake for service line air supply.
- Open the emergency line shutoff valve at the rear of the last trailer; audible air escaping confirms the system is charged.

Antilock Brakes

Converter dollies manufactured on or after March 1, 1998, are required to have a lamp on the left side to indicate the presence of antilock brakes.

Description

Test your knowledge on doubles and triples in commercial driving with this quiz. Learn about converter dollies, their components, and secure coupling methods. Perfect for CDL aspirants looking to deepen their understanding of combination vehicles.