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NJ CDL Doubles/Triples study materials
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NJ CDL Doubles/Triples practice questions

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Question 1Coupling and uncoupling twin trailers

When coupling the converter dolly to the rear trailer of a twin-trailer combination, what must be aligned before the dolly coupler will lock onto the trailer kingpin?

  1. The rear trailer's landing gear must be raised fully so the trailer tilts toward the dolly
  2. The dolly pintle hook must be latched to the trailer's rear crossmember before backing
  3. The dolly coupler jaws must be opened and the dolly raised so the jaws align with the kingpin Correct answer.
  4. The dolly must be backed under the trailer with the jaws closed so the kingpin forces them apart

Explanation

A converter dolly couples to the rear trailer through a fifth-wheel-type coupler that must be open and positioned at kingpin height. The jaws must be open so the kingpin can enter, and the dolly must be at the right height for the jaws to pass around the pin. Backing in with closed jaws or latching the pintle to the crossmember is not how the connection is made.

Question 2Coupling and uncoupling twin trailers

Before backing a tractor under the lead trailer's kingpin during a twin-trailer hookup, the trailer should be at what height relative to the tractor's fifth wheel?

  1. Level with the fifth wheel so the kingpin enters without touching the plate
  2. Slightly higher than the fifth wheel so the plate slides under the trailer Correct answer.
  3. Raised as high as the landing gear allows to clear the mud flaps
  4. Slightly lower than the fifth wheel so the trailer lifts the wheel on contact

Explanation

The trailer apron should sit slightly higher than the fifth wheel so the plate slides under the trailer and the kingpin drops into the jaws as the tractor backs in. Setting the trailer too low causes the kingpin to strike the plate or the tractor to push the trailer backward. Too high a setting risks the kingpin riding over the top of the fifth wheel.

Question 3Coupling and uncoupling twin trailers

After the tractor is coupled to the lead trailer in a doubles combination, what is the correct next step before the converter dolly is attached?

  1. Open the rear trailer's emergency relay valve to release its spring brakes
  2. Raise the lead trailer's landing gear and secure the tractor-trailer connection Correct answer.
  3. Connect the dolly to the rear trailer first, then back the lead trailer to it
  4. Lower the dolly landing gear and roll the dolly under the rear trailer

Explanation

The standard sequence is tractor to lead trailer first, with the connection checked and the landing gear raised. Only then is the dolly brought in and coupled to the lead trailer's rear, followed by the rear trailer. Coupling the dolly to the rear trailer before the lead trailer is secured reverses the safe order.

Question 4Coupling and uncoupling twin trailers

In a twin-trailer combination, what does the converter dolly's pintle hook connect to?

  1. The tractor's fifth wheel release handle
  2. The lead trailer's rear frame or pintle eye Correct answer.
  3. The rear trailer's landing gear cross tube
  4. The rear trailer's kingpin

Explanation

The converter dolly has a drawbar with a lunette or eye that engages the pintle hook mounted on the rear of the lead trailer. The dolly's own fifth wheel or coupler then carries the rear trailer's kingpin. The pintle hook does not touch the rear trailer's kingpin or the tractor.

Question 5Coupling and uncoupling twin trailers

When uncoupling twin trailers, why should the rear trailer's spring brakes be set and the trailer secured before the dolly coupler is released?

  1. So the dolly can be pulled forward without turning the wheels
  2. So the trailer cannot roll away once the dolly no longer holds it Correct answer.
  3. So the dolly's air lines can be bled of pressure quickly
  4. So the lead trailer's pintle hook can be opened by hand

Explanation

Once the dolly coupler is released, nothing holds the rear trailer in place except its own brakes and chocks. Setting the spring brakes and securing the wheels keeps the trailer from rolling during and after separation. The other choices describe steps or effects that are not the reason for securing the trailer.

Question 6Coupling and uncoupling twin trailers

Which air line must be connected between the tractor and the lead trailer to supply the trailer's spring brake system so it can be released?

  1. The electrical cord
  2. The emergency line Correct answer.
  3. The service line only
  4. The trailer light cable

Explanation

The emergency (supply) line charges the trailer's air tanks and releases the spring brakes when pressure builds. The service line carries application pressure from the brake valve. Without the emergency line connected, the trailer stays in a spring-braked condition.

Question 7Coupling and uncoupling twin trailers

What is the purpose of the converter dolly's safety chains or cable when connecting to the lead trailer?

  1. To carry the dolly's share of the trailer weight
  2. To keep the dolly attached if the pintle hook or drawbar fails Correct answer.
  3. To limit the turning angle of the rear trailer
  4. To prevent the dolly's air lines from dragging on the road

Explanation

Safety chains or a cable provide a secondary connection so the dolly does not separate completely if the primary pintle or drawbar fails. They are not load-bearing for weight and do not control air lines or turning geometry. They must be crossed or rigged as the manufacturer specifies so they cradle the drawbar if it drops.

Question 8Coupling and uncoupling twin trailers

After coupling a converter dolly to the lead trailer, a driver should perform a pull test. What does a proper pull test involve?

  1. Applying the trailer brakes and pulling gently forward against them Correct answer.
  2. Backing the combination while an observer watches the dolly wheels
  3. Revving the engine in neutral while holding the clutch
  4. Releasing the tractor parking brake and rolling forward several feet

Explanation

A pull test confirms the coupler is latched by applying the trailer brakes and easing forward against the resistance. If the coupling is not secure, it will separate during the test rather than on the road. Rolling freely forward or backing does not prove the latch has engaged.

Question 9Coupling and uncoupling twin trailers

When backing the tractor under the lead trailer's kingpin, the driver hears a distinct click and the fifth wheel handle moves into the locked position. What should the driver do next?

  1. Pull the release handle back out to verify it was latched
  2. Lower the landing gear before checking the jaws
  3. Get out and visually check that the jaws are closed around the kingpin Correct answer.
  4. Drive away immediately to confirm the coupling holds

Explanation

An audible click and a moving handle are encouraging but not proof of a secure coupling. The driver must stop, get out, and visually confirm the jaws are closed around the kingpin, then perform a pull test. Driving away without checking risks dropping the trailer.

Question 10Coupling and uncoupling twin trailers

A driver is uncoupling a set of triples and must separate the middle trailer from the rear dolly. Which action protects the middle trailer from rolling when the dolly is removed?

  1. Chock the dolly wheels and leave the middle trailer brakes released
  2. Set the middle trailer spring brakes and chock its wheels Correct answer.
  3. Disconnect the emergency line first to apply the dolly brakes
  4. Lower the middle trailer landing gear while the dolly is still attached

Explanation

With the dolly removed, the middle trailer depends entirely on its own spring brakes and chocks. Setting the spring brakes and chocking the wheels prevents movement during and after separation. Leaving brakes released or relying on the dolly's brakes does not protect the trailer once the dolly is gone.

Question 11Coupling and uncoupling twin trailers

During coupling, the dolly's upper coupler fails to latch onto the rear trailer kingpin even though the jaws are open and aligned. Which condition is the most likely cause?

  1. The tractor's fifth wheel is greased
  2. The dolly coupler is too low or too high relative to the kingpin Correct answer.
  3. The rear trailer's electrical cord is plugged in backward
  4. The lead trailer's pintle hook is latched

Explanation

A coupler that is misaligned vertically cannot capture the kingpin even with open jaws. The dolly must be raised or lowered, often with its landing gear or adjustment, until the jaws are at kingpin height. Electrical connections and pintle latching do not affect whether the jaws close.

Question 12Coupling and uncoupling twin trailers

Why must the tractor's trailer hand valve (spike) not be used to hold a twin-trailer combination during coupling or uncoupling?

  1. It applies all trailer brakes but does not hold the tractor
  2. It applies only the rear trailer brakes and locks the dolly
  3. It automatically releases the spring brakes on the rear trailer
  4. It applies only the lead trailer brakes and can release unexpectedly Correct answer.

Explanation

The hand valve supplies service air to the trailer brakes only and does not hold the tractor; it can also be knocked or released. Parking brakes and chocks are the reliable way to hold the combination. Relying on the hand valve during coupling can let the equipment roll.

Question 13Coupling and uncoupling twin trailers

A driver has coupled the lead trailer and dolly but has not yet connected the rear trailer. What should be done with the dolly's air lines and electrical cord in this intermediate state?

  1. Plug the dolly cord into the lead trailer's rear socket
  2. Leave them dragging to keep them accessible
  3. Tie them to the dolly's safety chains
  4. Secure them so they do not drag or get pinched Correct answer.

Explanation

Loose lines and cords can drag, chafe, or be crushed by tires while the dolly is moved or the rear trailer is positioned. They should be secured out of the way until connected. Dragging them or tying them to safety chains risks damage and interferes with the chains' function.

Question 14Coupling and uncoupling twin trailers

When coupling the rear trailer to the converter dolly, the trailer's kingpin should contact which part of the dolly first?

  1. The dolly's landing gear foot
  2. The dolly's safety chain eye
  3. The dolly's pintle hook
  4. The dolly's upper coupler plate and jaws Correct answer.

Explanation

The rear trailer's kingpin enters the dolly's upper coupler, where the plate guides it and the jaws close around it. The pintle hook is at the front of the dolly and connects to the lead trailer. Landing gear and chain eyes play no role in capturing the kingpin.

Question 15Coupling and uncoupling twin trailers

After fully coupling a set of doubles, the driver notices the rear trailer sits noticeably lower at the front than at the rear. What is the most appropriate response?

  1. Drive it because ride height does not affect coupling
  2. Loosen the dolly's pintle hook to let the trailer settle
  3. Increase air pressure in the rear trailer tires to level it
  4. Check that the dolly coupler is fully seated and the landing gear is raised Correct answer.

Explanation

A trailer that sits low at the front suggests the coupler is not fully seated or the landing gear is still carrying weight. The driver should verify the coupling is seated and the landing gear fully raised before moving. Adjusting tire pressure or loosening the pintle does not correct a coupling problem.

Question 16Coupling and uncoupling twin trailers

What is the correct order for connecting the air lines when coupling a converter dolly to the lead trailer and rear trailer?

  1. Service line, electrical cord, then emergency line
  2. Electrical cord first, then service line, then emergency line
  3. Service line first, then emergency line, then electrical cord
  4. Emergency line first, then service line, then electrical cord Correct answer.

Explanation

The emergency (supply) line is connected first so the trailer reservoirs charge and the spring brakes release, which prevents dragging brakes. The service line and then the electrical cord follow. Connecting the service line first leaves the trailer spring-braked and can cause drag or damage.

Question 17Coupling and uncoupling twin trailers

A driver is preparing to uncouple a set of doubles on a slight grade. Besides setting the spring brakes, what is the best practice for the rear trailer?

  1. Turn the steering tires toward the curb and rely on them
  2. Chock the wheels and lower the landing gear before releasing the dolly coupler Correct answer.
  3. Disconnect the service line first to apply the brakes
  4. Leave the landing gear up so the dolly can be pulled straight out

Explanation

On a grade, chocks and properly set landing gear are the reliable protection against rolling once the dolly is released. Landing gear should be lowered to support the trailer before the coupler is opened. Relying on steering geometry or line order does not secure the trailer.

Question 18Coupling and uncoupling twin trailers

During a pre-trip inspection of a coupled twin-trailer combination, which item confirms the dolly's upper coupler is properly engaged with the rear trailer?

  1. The electrical cord is plugged into the rear trailer
  2. The dolly's landing gear is fully raised
  3. The locking jaws are closed around the kingpin and the release handle is seated Correct answer.
  4. The safety chains are crossed under the drawbar

Explanation

Proper engagement is confirmed by closed jaws around the kingpin and a seated release handle, backed up by a pull test. Raised landing gear, crossed chains, and a plugged cord are necessary but do not prove the coupler has captured the pin. Visual inspection of the jaws is the direct check.

Question 19Coupling and uncoupling twin trailers

Why is it important to check that the converter dolly's drawbar is level or nearly level after coupling to the lead trailer?

  1. A level drawbar is required for the electrical cord to reach
  2. A tilted drawbar changes the color of the dolly's marker lights
  3. A level drawbar prevents the pintle hook from opening
  4. A tilted drawbar can cause poor tracking and uneven tire loading Correct answer.

Explanation

Drawbar angle affects how the dolly tracks and how weight is distributed on the dolly tires and pintle. An excessively tilted drawbar can cause poor tracking, tire wear, and handling problems. Marker lights, cord reach, and pintle locking are not governed by drawbar level.

Question 20Coupling and uncoupling twin trailers

When uncoupling the lead trailer from the tractor in a doubles set, the landing gear should be lowered until what condition is met before the fifth wheel is released?

  1. The landing gear touches the ground and the trailer is supported Correct answer.
  2. The landing gear is fully extended to its maximum height
  3. The trailer's rear wheels lift off the ground
  4. The landing gear crank becomes hard to turn

Explanation

The landing gear must contact the ground and take the trailer's weight so it does not drop when the fifth wheel is released. Cranking to maximum height or until the crank binds can leave the gear overloaded or the trailer unsupported. The trailer wheels should stay on the ground.

Question 21Coupling and uncoupling twin trailers

A driver coupling a set of triples finds the middle trailer's kingpin will not enter the dolly jaws because the trailer has shifted sideways. What is the safest correction?

  1. Open the jaws wider with a pry bar and back in
  2. Reposition the trailer or dolly so the kingpin aligns with the jaws Correct answer.
  3. Force the dolly under the trailer by driving forward sharply
  4. Lower the dolly coupler below the kingpin and lift it with the trailer

Explanation

Lateral misalignment is corrected by repositioning the trailer or dolly so the kingpin lines up with the open jaws. Forcing, prying, or lifting with the trailer damages the coupler and is unsafe. Patience and proper alignment prevent injury and equipment damage.

Question 22Coupling and uncoupling twin trailers

In a set of triples, the rear dolly's emergency line is connected but the middle trailer's emergency line is not. What is the expected result when the driver releases the parking brake?

  1. All trailers release and the combination rolls normally
  2. The rear trailer loses its brakes but the middle trailer releases
  3. The middle trailer stays spring-braked and its wheels may drag Correct answer.
  4. The tractor's spring brakes will not release

Explanation

Each trailer must receive emergency air to release its spring brakes. If the middle trailer's emergency line is not connected, that trailer stays spring-braked and its wheels will drag when the combination moves. The tractor and other trailers are unaffected by that missing connection.

Question 23Coupling and uncoupling twin trailers

A driver must uncouple the rear trailer from a converter dolly on soft ground. Which combination of precautions best prevents the dolly from sinking or tipping during separation?

  1. Leave the dolly attached to the lead trailer and drag the rear trailer off
  2. Use blocks under the dolly landing gear and keep the dolly coupled until the trailer is supported Correct answer.
  3. Deflate the dolly tires slightly to increase the footprint
  4. Release the dolly coupler first, then lower the landing gear into the soft ground

Explanation

Soft ground requires spreading the load with blocks under the landing gear and ensuring the trailer is supported before the coupler is released. Releasing first lets the dolly or trailer drop and tip. Dragging the trailer or deflating tires does not provide stable support.

Question 24Coupling and uncoupling twin trailers

During a pull test on a newly coupled rear trailer, the trailer moves a few inches and then stops while the tractor tires spin slightly. What does this indicate?

  1. The trailer brakes are holding and the coupling is resisting the pull Correct answer.
  2. The coupler jaws are not latched and the trailer is separating
  3. The electrical cord is disconnected
  4. The dolly landing gear is still on the ground

Explanation

A successful pull test shows the trailer brakes holding while the tractor strains against the coupling, so slight tire spin with no separation is normal. If the jaws were not latched, the trailer would separate from the dolly. Landing gear position and electrical connection are checked separately.

Question 25Coupling and uncoupling twin trailers

A driver is coupling a set of doubles alone and must move between the tractor cab and the rear trailer during the procedure. Which practice best manages the risk of the combination moving unexpectedly?

  1. Rely on the trailer hand valve to hold the combination while outside
  2. Set the parking brake, place the transmission in neutral or park, and chock as needed before leaving the cab Correct answer.
  3. Leave the tractor in gear with the parking brake released for quick adjustment
  4. Keep the engine running at high idle to maintain air pressure

Explanation

Before leaving the cab, the driver must set the parking brake, secure the transmission, and chock if needed so the combination cannot roll. Leaving the tractor in gear with the brake released or relying on the hand valve creates a serious runaway risk. High idle does not secure the vehicle.

Question 26Coupling and uncoupling twin trailers

When coupling a converter dolly to the lead trailer of a doubles set, which component of the dolly attaches to the lead trailer's rear frame area to keep the dolly aligned and prevent it from swinging?

  1. The dolly's spring brake chambers
  2. The dolly's drawbar and its locking pin or latch Correct answer.
  3. The dolly's landing gear legs
  4. The dolly's upper coupler plate

Explanation

The drawbar is the arm on the converter dolly that reaches forward and locks onto the lead trailer's rear frame, holding the dolly in line behind the trailer. The upper coupler on top of the dolly is what the rear trailer's kingpin locks into, not what attaches to the lead trailer.

Question 27Coupling and uncoupling twin trailers

In a twin-trailer combination, what is the primary function of the converter dolly?

  1. It increases the braking force of the lead trailer's spring brakes.
  2. It converts the lead trailer's electrical system to 12 volts.
  3. It serves as a spare axle that can be dropped to reduce weight.
  4. It carries the rear trailer's kingpin and provides a fifth wheel and axle so a second trailer can be towed. Correct answer.

Explanation

A converter dolly is a small frame with one or two axles, a fifth wheel on top, and a drawbar that attaches to the lead trailer. It gives the rear trailer a coupling point and its own supporting axle so the combination can articulate.

Question 28Coupling and uncoupling twin trailers

Before backing the tractor under the lead trailer's kingpin during coupling, the trailer should be at what height relative to the fifth wheel?

  1. The trailer apron should be slightly below the fifth wheel so the plate lifts it as you back under. Correct answer.
  2. The trailer height does not matter as long as the kingpin is greased.
  3. The trailer should be raised so the kingpin clears the fifth wheel by at least six inches.
  4. The trailer should be lowered until the landing gear is off the ground.

Explanation

The trailer should be positioned so the leading edge of the apron is just below the fifth wheel plate, letting the plate ride up under the trailer as the tractor backs in. That prevents the tractor from striking and damaging the trailer and lets the kingpin seat in the jaws.

Question 29Coupling and uncoupling twin trailers

After the fifth wheel jaws have closed on the lead trailer's kingpin, which visual check confirms the coupling is secure?

  1. The fifth wheel handle is in the closed position and the jaws are visible around the kingpin shank with no gap. Correct answer.
  2. The dolly's drawbar pin is inserted.
  3. The trailer's landing gear crank is stowed.
  4. The trailer's ABS light is off.

Explanation

Looking under the trailer, the jaws should be closed around the kingpin shank with the release handle fully in and the safety latch engaged. That visual check, backed by a pull test, is what confirms the kingpin is captured.

Question 30Coupling and uncoupling twin trailers

A driver is coupling a converter dolly to the rear of the lead trailer and notices the drawbar eye sits several inches too high to line up with the lead trailer's pintle hook. What is the appropriate action?

  1. Adjust the dolly's drawbar height or the lead trailer's pintle hook height so the eye and hook align squarely, then lock the pin. Correct answer.
  2. Force the drawbar down with the dolly's landing gear and lock it in place.
  3. Leave the drawbar unlocked so it can find its own alignment while towing.
  4. Couple it anyway; the pintle hook will pull the eye down once the tractor moves.

Explanation

The drawbar eye and pintle hook must line up so the pin seats fully and the drawbar rides level. Height is adjusted with the dolly landing gear or the drawbar adjustment provided before the pin is locked. Forcing a misaligned coupling or towing unlocked can damage the hook or let the dolly separate.

Question 31Coupling and uncoupling twin trailers

When connecting the air lines between the tractor and a twin-trailer combination, which line supplies air to the trailer spring brake chambers to release them?

  1. The service line (blue).
  2. The emergency line (red). Correct answer.
  3. The electrical cord.
  4. The dolly's auxiliary supply hose.

Explanation

The emergency line, usually red, charges the trailer reservoirs and supplies the air that releases the spring brakes when the system is charged. The service line, usually blue, applies the service brakes when the brake pedal or hand valve is used.

Question 32Coupling and uncoupling twin trailers

A driver has connected the dolly's air lines to the lead trailer but has not yet coupled the rear trailer. What should be done with the dolly's spring brakes before moving the tractor and lead trailer?

  1. Disconnect the dolly's brake chambers to prevent drag.
  2. Leave them released so the dolly can roll freely.
  3. Apply the dolly's spring brakes by ensuring the emergency line is charged and the parking brake is set, or by using the dolly's own parking brake control. Correct answer.
  4. Chock only the rear trailer wheels.

Explanation

An uncoupled dolly can roll away if its spring brakes are released. With the emergency line charged and the parking control set, the dolly's spring brakes stay applied until you are ready to couple and release them deliberately.

Question 33Coupling and uncoupling twin trailers

During a pull test after coupling the rear trailer to the converter dolly, the trailer moves a few inches and then stops hard while the tractor tires spin slightly. What does this indicate?

  1. The dolly's drawbar pin has popped out.
  2. The trailer brakes are holding and the coupling is secure.
  3. The kingpin is properly locked and the movement was slack being taken up.
  4. The kingpin is not locked and the trailer is being dragged by the dolly. Correct answer.

Explanation

In a proper pull test the trailer should not move at all if the kingpin is locked and the trailer brakes are set. If the trailer slides or drags while the tractor pulls, the jaws are not holding the kingpin and the coupling must be redone.

Question 34Coupling and uncoupling twin trailers

When uncoupling a set of doubles, in what order should the connections between the lead trailer and the converter dolly be separated?

  1. Disconnect the electrical cord and air lines first, then release the drawbar pin and lower the dolly. Correct answer.
  2. Release the drawbar pin while the air lines remain connected to keep the dolly brakes released.
  3. Release the drawbar pin first, then disconnect the air lines and electrical cord.
  4. Disconnect only the electrical cord, then drive away.

Explanation

The electrical cord and air lines are disconnected before the mechanical connection is released so the dolly cannot roll while hoses are still attached and get damaged. With the lines off, the dolly's spring brakes apply and the drawbar pin can be safely released.

Question 35Coupling and uncoupling twin trailers

A driver is dropping a converter dolly on uneven ground after uncoupling it from the lead trailer. Which practice best prevents the dolly from tipping or rolling?

  1. Lower the dolly's landing gear until it bears firmly on level ground and set the dolly's spring brakes. Correct answer.
  2. Rest the dolly on its upper coupler plate so it cannot roll.
  3. Lower the landing gear only until it just touches, then rely on the drawbar to hold it.
  4. Leave the dolly resting on its drawbar with the wheels chocked.

Explanation

A dropped dolly should rest on landing gear that is firmly set on solid, reasonably level ground with its spring brakes applied. That keeps the dolly stable and prevents it from rolling or tipping while it is unattached.

Question 36Coupling and uncoupling twin trailers

In a set of triples, why must the middle trailer's emergency (supply) line be connected to the rear dolly before the combination is moved?

  1. It provides the electrical ground for the rear trailer lights.
  2. It supplies air only to the middle trailer's service brakes.
  3. It charges the rear dolly's air reservoirs so its spring brakes can release and its brakes can function. Correct answer.
  4. It is needed only when the rear trailer is loaded.

Explanation

The emergency line carries supply air rearward so each downstream reservoir, including the rear dolly's, is charged. Without it the rear dolly's spring brakes stay applied and its brakes cannot release or modulate properly.

Question 37Coupling and uncoupling twin trailers

A driver coupling a set of doubles alone must move between the cab and the rear trailer during the procedure. Which practice best manages the risk of the combination moving unexpectedly?

  1. Leave the driver's door open as a signal to other traffic.
  2. Leave the tractor running in gear with the parking brake released so it is ready to move.
  3. Rely on the trailer spring brakes alone to hold the combination.
  4. Set the tractor parking brakes, place the transmission in neutral or park, and chock the wheels before leaving the cab. Correct answer.

Explanation

Whenever the driver leaves the cab during coupling, the tractor parking brakes should be set and the transmission placed in a holding position, with wheels chocked if there is any grade. That prevents the combination from rolling while the driver is between the units.

Question 38Coupling and uncoupling twin trailers

A driver has coupled the lead trailer to the tractor and the dolly to the lead trailer, but the rear trailer is not yet attached. How should the dolly's spring brakes be handled while the driver positions the rear trailer?

  1. Release them so the dolly can be pushed by hand into alignment.
  2. Apply them only after the rear trailer is coupled.
  3. Keep them applied by leaving the emergency line charged and the parking control set, releasing them only when ready to couple and pull. Correct answer.
  4. Remove the dolly's brake chambers so it rolls freely.

Explanation

The dolly should stay braked whenever it is unattached on the rear, so it cannot roll while the driver maneuvers the rear trailer. The spring brakes release once the system is charged and the driver deliberately releases the parking control.

Question 39Coupling and uncoupling twin trailers

During a pre-trip inspection of a coupled doubles combination, the driver finds the dolly's drawbar rides noticeably nose-down relative to the lead trailer's pintle hook. Why does this matter?

  1. It can cause uneven tire loading, poor tracking, and abnormal wear or stress on the drawbar and hook. Correct answer.
  2. It means the rear trailer's kingpin is not locked.
  3. It indicates the dolly's spring brakes are dragging.
  4. It shows the electrical cord is too short.

Explanation

The drawbar should ride level or nearly level so the load transfers evenly and the dolly tracks properly behind the lead trailer. A pronounced nose-down or nose-up attitude loads the drawbar and pintle hook abnormally and can cause poor tracking and tire wear.

Question 40Coupling and uncoupling twin trailers

A driver is coupling the rear trailer to a converter dolly on a slight downhill grade. Which combination of precautions best prevents the rear trailer from rolling into the dolly as the tractor backs up?

  1. Chock the rear trailer's wheels and keep its spring brakes applied until the kingpin is locked. Correct answer.
  2. Release the rear trailer's spring brakes and let it roll downhill onto the dolly.
  3. Rely on the trailer's spring brakes alone and back up quickly to engage the kingpin.
  4. Have a helper stand behind the trailer to stop it by hand.

Explanation

On a grade the rear trailer must be held by chocks as well as its spring brakes so it cannot roll while the dolly is positioned under the kingpin. Only after the kingpin is locked and a pull test is passed should the chocks be removed.

Question 41Inspecting converter dollies and the second trailer

When coupling a converter dolly to the rear of the first trailer, the locking jaws of the dolly coupler must close around which component?

  1. The second trailer's landing gear foot
  2. The safety chain anchor ring
  3. The dolly's own drawbar eye
  4. The kingpin of the first trailer Correct answer.

Explanation

The dolly coupler works exactly like a tractor fifth wheel: its jaws must fully close and lock around the first trailer's kingpin. A positive lock is confirmed by a visual check and a firm pull test on the dolly.

Question 42Inspecting converter dollies and the second trailer

After backing the dolly under the first trailer's rear apron and hearing the coupler latch, what is the correct next step before connecting air lines?

  1. Open the dolly air tank drain cocks
  2. Pull the tractor and dolly forward while holding the trailer brakes to test the lock Correct answer.
  3. Lower the landing gear to take the weight off the dolly
  4. Raise the dolly drawbar to its highest position

Explanation

A pull test confirms the coupler jaws are actually locked around the kingpin rather than resting on top of it. Applying the trailer brakes and easing forward makes any false coupling separate immediately at low speed.

Question 43Inspecting converter dollies and the second trailer

Which component on a converter dolly carries the weight of the dolly frame when it is not coupled to a trailer?

  1. The coupler jaw wedge
  2. The dolly landing gear or support leg Correct answer.
  3. The gladhand shut-off valve
  4. The drawbar spring hanger

Explanation

An uncoupled dolly rests on its own landing gear or support leg, which must be lowered before the dolly is dropped. This keeps the coupler plate at a workable height and prevents the dolly from tipping.

Question 44Inspecting converter dollies and the second trailer

The air lines running from the dolly to the second trailer are most commonly color-coded in which way?

  1. Blue for service, red for emergency, black for supply Correct answer.
  2. Red for service, blue for emergency, black for supply
  3. Yellow for service, red for emergency, blue for supply
  4. Green for service, black for emergency, red for supply

Explanation

Standard color coding is blue for the service line, red for the emergency line, and black for the supply line. Correct gladhand pairing keeps the service and emergency functions from being crossed.

Question 45Inspecting converter dollies and the second trailer

When connecting gladhands between the dolly and the second trailer, the couplers should be aligned so that the rubber seals meet and the handles turn in which direction?

  1. Either direction, since gladhands are not directional
  2. Upward against spring pressure
  3. Sideways toward the frame rail
  4. Downward into the locked detent Correct answer.

Explanation

Gladhands are locked by turning the handles down so they seat in the detent, which compresses the seals together. Turning them the wrong way leaves the couplers loose and allows air to escape.

Question 46Inspecting converter dollies and the second trailer

Before a loaded set of doubles is moved, the second trailer's landing gear must be in what condition?

  1. Fully extended and touching the ground
  2. Removed and stored on the dolly
  3. Cranked fully up and secured Correct answer.
  4. Lowered halfway for stability

Explanation

Landing gear must be fully retracted and pinned or secured before the second trailer is towed. Extended gear can strike the road, railroad crossings, or the dolly during turns.

Question 47Inspecting converter dollies and the second trailer

The safety chains between the dolly and the second trailer should be rigged so that they:

  1. Drag lightly on the pavement to show they are attached
  2. Are wrapped tightly around the drawbar to prevent any movement
  3. Cross under the drawbar with enough slack to allow turns but short enough to catch a separation Correct answer.
  4. Are hooked to the same point as the air lines

Explanation

Safety chains are a backup connection: they must have enough slack for articulation yet be short enough to hold the drawbar off the ground if the coupling fails. Crossing them helps cradle the drawbar if it drops.

Question 48Inspecting converter dollies and the second trailer

A driver finds the dolly coupler jaw will not close fully around the first trailer's kingpin. What is the most likely cause?

  1. The jaw is misaligned or the locking mechanism is damaged or dry Correct answer.
  2. The second trailer is too light
  3. The dolly air tank is overcharged
  4. The kingpin is too far forward in the fifth wheel throat

Explanation

A jaw that will not close usually indicates misalignment, a bent jaw, a broken lock, or a dry mechanism that needs lubrication. Forcing it or driving with a partial latch risks a dropped trailer.

Question 49Inspecting converter dollies and the second trailer

How should the dolly drawbar height be set before backing toward the second trailer's pintle eye?

  1. Set at the highest available setting regardless of the eye
  2. Set level with the pintle eye so the drawbar enters straight Correct answer.
  3. Set several inches above the eye so it drops into place
  4. Set several inches below the eye so it lifts into place

Explanation

The drawbar should be level with the pintle eye so the eye slides on without binding or lifting the trailer. Height is adjusted with the dolly landing gear and the tractor's suspension.

Question 50Inspecting converter dollies and the second trailer

What is the purpose of the pintle hook on a converter dolly?

  1. It holds the dolly's landing gear in the raised position
  2. It receives the drawbar eye of the second trailer Correct answer.
  3. It regulates air pressure to the second trailer brakes
  4. It locks the dolly to the tractor fifth wheel

Explanation

The pintle hook at the rear of the dolly captures the second trailer's drawbar eye and locks it with a latch. The latch must be secured with its safety pin or latch clip before travel.