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

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Question 1Coupling and Uncoupling Multiple Trailers

When coupling a tractor to the first semitrailer, at what point should you back under the trailer until you hear the kingpin lock into the fifth wheel?

  1. Back at normal speed so the kingpin seats firmly
  2. Back slowly until the fifth wheel contacts the kingpin and the locking jaws snap shut Correct answer.
  3. Back until the trailer landing gear lifts off the ground
  4. Stop as soon as the trailer apron touches the fifth wheel plate

Explanation

The coupling procedure requires backing slowly and steadily so the kingpin slides into the fifth wheel and the jaws close with an audible click. Backing fast can damage the jaws or miss the kingpin, and stopping early leaves the trailer uncoupled.

Question 2Coupling and Uncoupling Multiple Trailers

After the fifth wheel jaws close on the kingpin, what is the correct next step before you begin pulling the trailer?

  1. Pull the release handle to confirm the jaws are open
  2. Release the tractor parking brake and drive forward to test the lock
  3. Do a tug test by pulling gently forward against the locked trailer brakes Correct answer.
  4. Lower the landing gear fully to the ground

Explanation

A tug test confirms the kingpin is actually captured by the jaws. With the trailer brakes set, you pull gently forward and feel resistance; if the tractor moves freely, the coupling failed. This check catches a high hook before it becomes a dropped trailer.

Question 3Coupling and Uncoupling Multiple Trailers

You are coupling a tractor to a converter dolly that will pull a second trailer. Where must the dolly be positioned relative to the first trailer before coupling?

  1. Underneath the first trailer's rear frame
  2. In front of the tractor to lead the combination
  3. Directly behind the first trailer with its drawbar facing rearward Correct answer.
  4. Beside the tractor so the air lines reach

Explanation

A converter dolly is coupled to the rear of the first trailer, with its drawbar or tongue attaching to the first trailer's rear and its fifth wheel supporting the second trailer's kingpin. Positioning it behind the first trailer aligns the drawbar for connection.

Question 4Coupling and Uncoupling Multiple Trailers

When connecting the air lines between the first trailer and the converter dolly, which line supplies air to release the dolly's spring brakes?

  1. The service line (blue)
  2. The supply line (red) Correct answer.
  3. The emergency line (red)
  4. The electrical cord

Explanation

The emergency (supply) line, commonly color-coded red, charges the trailer air tanks and releases spring brakes when charged. The service line, usually blue, applies the brakes during a brake application. Confusing the two leaves the dolly brakes locked or unreleased.

Question 5Coupling and Uncoupling Multiple Trailers

While uncoupling the rear trailer from the converter dolly, what should you do with the dolly's air lines before pulling away?

  1. Leave them connected so they drag free
  2. Coil them around the dolly tongue
  3. Cap them with tape and let them hang
  4. Disconnect them and secure the gladhands to their dummy couplers Correct answer.

Explanation

Air lines should be disconnected and the gladhands stored on dummy couplers to protect the seals and keep the lines off the ground. Leaving lines connected or dragging damages couplers and can tear the lines loose.

Question 6Coupling and Uncoupling Multiple Trailers

Before lowering the landing gear on the rear trailer during uncoupling, what must be true about the trailer?

  1. The tractor must be in gear
  2. The ground under the landing gear must be firm and level Correct answer.
  3. The trailer brakes must be released
  4. The trailer must be resting on the dolly only

Explanation

Landing gear must be lowered onto firm, level ground so the trailer does not sink or tip once the tractor or dolly is removed. Soft or sloped ground can cause the trailer to settle and become unstable.

Question 7Coupling and Uncoupling Multiple Trailers

What is the purpose of the converter dolly's pintle hook or drawbar connection?

  1. It links the dolly to the rear of the first trailer Correct answer.
  2. It holds the second trailer's kingpin
  3. It releases the dolly's spring brakes
  4. It stores the dolly's air lines

Explanation

The dolly's drawbar or tongue ends in an eye or ring that attaches to the pintle hook on the rear of the first trailer. This connection transmits the towing force from the first trailer to the dolly.

Question 8Coupling and Uncoupling Multiple Trailers

After coupling the dolly to the first trailer, you notice the safety chains are crossed under the drawbar. What is the correct action?

  1. Reattach the chains so they do not drag or bind Correct answer.
  2. Shorten the chains so they cannot reach the ground
  3. Remove the chains because the pintle hook is enough
  4. Leave them crossed; that is the required arrangement

Explanation

Safety chains should be attached so they do not drag on the ground or bind on the drawbar, while still allowing turning. Chains that drag wear through, and crossed or binding chains can restrict articulation.

Question 9Coupling and Uncoupling Multiple Trailers

When uncoupling a set of doubles, why should you uncouple the rear trailer first?

  1. It is required to drain the air tanks
  2. It prevents the first trailer's brakes from setting
  3. It keeps the dolly from rolling away
  4. It allows you to keep the tractor attached to the first trailer for stability Correct answer.

Explanation

Uncoupling from the rear forward keeps the tractor attached to the lead trailer, providing a stable anchor while you drop the rear trailer and dolly. Working rear-first also matches the reverse of the coupling sequence.

Question 10Coupling and Uncoupling Multiple Trailers

During a pre-trip inspection of a doubles combination, you find the dolly's fifth wheel jaws will not close around the second trailer's kingpin. What is the most likely cause?

  1. The dolly's air tanks are fully charged
  2. The trailer brakes are set
  3. The jaws are adjusted too loosely or the pin is misaligned Correct answer.
  4. The kingpin is too far forward in the fifth wheel opening

Explanation

Jaws that will not close usually indicate a misaligned kingpin or an improperly adjusted locking mechanism. The kingpin must enter the throat squarely, and the jaw adjustment must be within tolerance for a secure lock.

Question 11Coupling and Uncoupling Multiple Trailers

What is a high hook, and why is it dangerous in a doubles operation?

  1. The kingpin rests on top of the closed jaws instead of being locked inside them Correct answer.
  2. The dolly is coupled at an upward angle to the first trailer
  3. The landing gear is raised too high before coupling
  4. The gladhands are connected above the frame

Explanation

A high hook occurs when the trailer is backed onto the fifth wheel but the kingpin sits on top of the jaws rather than locking inside them. The trailer appears coupled but can separate from the tractor or dolly once you drive, causing a serious crash.

Question 12Coupling and Uncoupling Multiple Trailers

You are backing the tractor under the first trailer. The trailer begins to move rearward as you back. What does this indicate?

  1. The trailer brakes are released and the kingpin has not locked Correct answer.
  2. The gladhands are crossed
  3. The landing gear is too low
  4. The fifth wheel is properly locked

Explanation

If the trailer rolls backward while you back under it, the trailer brakes are not holding and the kingpin has not yet engaged the jaws. Stop, set the trailer brakes, and reposition before continuing to avoid pushing the trailer.

Question 13Coupling and Uncoupling Multiple Trailers

Which combination of trailers is commonly referred to as a set of doubles in California?

  1. Two semitrailers pulled by one tractor with a converter dolly Correct answer.
  2. A tractor pulling one semitrailer and a full trailer on a drawbar
  3. A truck and a single semitrailer
  4. Three trailers joined by two dollies

Explanation

Doubles typically consist of a tractor, a semitrailer, a converter dolly, and a second semitrailer. The dolly provides the fifth wheel that supports the second trailer's kingpin.

Question 14Coupling and Uncoupling Multiple Trailers

Before you begin coupling a second trailer to the dolly, what should you verify about the dolly's fifth wheel?

  1. That the jaws are open and the release handle is in the locked position Correct answer.
  2. That the jaws are closed and greased
  3. That the dolly is chocked on all sides
  4. That the fifth wheel is tilted fully forward

Explanation

The fifth wheel jaws must be open so the kingpin can enter, and the release handle must be in the locked position so the jaws close and stay closed after coupling. A handle left open allows the jaws to release under load.

Question 15Coupling and Uncoupling Multiple Trailers

What should you do with the trailer's spring brakes before backing the tractor under it for coupling?

  1. Set them so the trailer stays put during coupling Correct answer.
  2. Disconnect the relay valve
  3. Pump them several times to build pressure
  4. Release them so the trailer can roll into alignment

Explanation

The trailer spring brakes must be set so the trailer does not roll while you back under it. With brakes set, any rearward creep signals a coupling problem rather than normal movement.

Question 16Coupling and Uncoupling Multiple Trailers

When uncoupling the dolly from the first trailer, what must be done with the dolly's landing gear or support before releasing the pintle hook?

  1. The dolly's air tanks must be drained
  2. The dolly's wheels must be removed
  3. The dolly's fifth wheel must be tilted forward
  4. The dolly must be supported so it does not tip when the drawbar is released Correct answer.

Explanation

A converter dolly can tip forward or fall when the drawbar is released if it is not supported. Lowering the dolly's support leg or landing gear keeps it stable until you move the tractor away.

Question 17Coupling and Uncoupling Multiple Trailers

After completing a coupling, you walk around the combination. What are you specifically checking on the air lines between the first trailer and the dolly?

  1. That they cross over the drawbar
  2. That they are disconnected
  3. That they are routed to avoid chafing and have enough slack for turns Correct answer.
  4. That they are tied tightly to the frame

Explanation

Air lines must be routed to prevent chafing and snagging while allowing enough slack for articulation during turns. Lines tied too tightly can pull apart, and lines left disconnected will not supply air.

Question 18Coupling and Uncoupling Multiple Trailers

Why is a walk-around inspection especially important after coupling doubles or triples?

  1. It allows you to skip the brake test
  2. It confirms each connection point and air line is secure before moving Correct answer.
  3. It is required only for single trailers
  4. It replaces the need for a tug test

Explanation

A doubles combination has multiple connection points-fifth wheels, pintle hooks, safety chains, and air lines-so a walk-around confirms each is secure. It supplements, but does not replace, the tug test and brake check.

Question 19Coupling and Uncoupling Multiple Trailers

You are coupling the second trailer to the dolly and the trailer's kingpin is slightly too high to enter the fifth wheel throat. What is the correct adjustment?

  1. Release the dolly's brakes
  2. Back the tractor faster to force engagement
  3. Lower the landing gear to raise the trailer
  4. Raise the landing gear to lower the trailer nose Correct answer.

Explanation

If the kingpin rides too high, raising the landing gear lowers the trailer nose so the kingpin aligns with the fifth wheel throat. Forcing engagement or moving fast can damage the jaws or cause a high hook.

Question 20Coupling and Uncoupling Multiple Trailers

What does the tractor protection valve do when the air pressure in a doubles combination drops to a low level?

  1. It disconnects the electrical cord
  2. It releases the spring brakes on all trailers
  3. It closes and traps air in the tractor, applying trailer brakes Correct answer.
  4. It increases pressure to the rear trailer

Explanation

The tractor protection valve closes at low pressure to keep enough air in the tractor for braking and signals the trailers to apply their spring brakes. This protects against a total loss of air from a broken line in the combination.

Question 21Coupling and Uncoupling Multiple Trailers

When performing a brake test on a doubles combination, what should happen when you apply the hand valve?

  1. The trailer brakes apply without the tractor service brakes Correct answer.
  2. Only the tractor brakes apply
  3. Only the rear trailer brakes apply
  4. The spring brakes release

Explanation

The hand valve (trailer parking valve) applies air to the trailer service brakes only, allowing you to check that trailer brakes work independently of the tractor foot brake. This confirms the trailer brake system is functioning.

Question 22Coupling and Uncoupling Multiple Trailers

What is the main risk of pulling a set of doubles with the dolly's safety chains not attached?

  1. The electrical lights will not work
  2. The dolly brakes will not release
  3. The rear trailer will track too wide
  4. The dolly could separate from the first trailer if the pintle hook fails Correct answer.

Explanation

Safety chains provide a backup connection if the pintle hook or drawbar fails. Without them, a broken coupling lets the dolly and rear trailer break free, creating an uncontrolled hazard.

Question 23Coupling and Uncoupling Multiple Trailers

During uncoupling, you lower the rear trailer's landing gear but the trailer's nose is still too high for the dolly to clear. What should you do?

  1. Release the dolly's fifth wheel jaws while the trailer is supported
  2. Lower the landing gear further to raise the nose
  3. Pull the tractor forward quickly to break the connection
  4. Raise the landing gear slightly to lower the nose and clear the dolly Correct answer.

Explanation

Adjusting the landing gear changes the trailer nose height so the kingpin clears the dolly's fifth wheel. The trailer must be properly supported before the jaws are released, and pulling away with the kingpin still engaged damages the equipment.

Question 24Coupling and Uncoupling Multiple Trailers

How many trailers are in a triples combination, and how many converter dollies are typically used?

  1. Three trailers with two dollies Correct answer.
  2. Three trailers with one dolly
  3. Two trailers with two dollies
  4. Two trailers with one dolly

Explanation

Triples consist of three trailers joined by two converter dollies, one between each pair of trailers. Each dolly provides a fifth wheel for the trailer behind it.

Question 25Coupling and Uncoupling Multiple Trailers

After coupling a converter dolly to the first trailer, you notice the dolly's drawbar eye does not sit flat in the pintle hook. What is the concern?

  1. The pintle hook latch may not close fully, allowing separation Correct answer.
  2. The dolly's brakes will overheat
  3. The first trailer's landing gear will fail
  4. The electrical cord will short out

Explanation

The drawbar eye must seat fully in the pintle hook so the latch can close and lock. An improperly seated eye prevents the latch from closing, and the dolly can separate from the first trailer under load.

Question 26Coupling and Uncoupling Multiple Trailers

When you lower the landing gear on a trailer that will be part of a doubles set, what should you do after the legs contact the ground?

  1. Leave the legs just touching the ground so the trailer settles onto the dolly
  2. Crank the legs down a few extra turns so the trailer is lifted slightly off the fifth wheel Correct answer.
  3. Retract the legs fully so the trailer rests on the dolly
  4. Crank only until the legs touch, then stop and rely on the dolly to hold the weight

Explanation

Landing gear must be cranked down enough to take the trailer's weight off the fifth wheel before you pull the tractor or dolly away. A few extra turns after ground contact lifts the trailer slightly and frees the jaws. If the legs only touch, the weight stays on the fifth wheel and the trailer can drop or drag when you pull out.

Question 27Coupling and Uncoupling Multiple Trailers

In a typical doubles combination, what does the converter dolly carry?

  1. A pintle hook only, with no fifth wheel
  2. The tractor's own fifth wheel assembly
  3. A set of landing gear for the rear trailer
  4. A fifth wheel that holds the kingpin of the rear trailer Correct answer.

Explanation

The converter dolly is a small axle unit with its own fifth wheel on top. That fifth wheel accepts the kingpin of the trailer behind it, while the dolly's drawbar attaches to the pintle hook of the trailer ahead. The dolly does not carry the tractor's fifth wheel or a set of landing gear for another trailer.

Question 28Coupling and Uncoupling Multiple Trailers

You are preparing to couple a dolly to the first trailer. Where should the dolly's drawbar eye end up relative to the trailer's pintle hook?

  1. Resting on top of the pintle hook so it can slide into place
  2. Angled upward so the eye can drop onto the hook as you pull forward
  3. Centered and flat in the pintle hook with the latch closed Correct answer.
  4. Hanging below the pintle hook with slack in the chains

Explanation

The drawbar eye must sit centered and flat inside the pintle hook, with the latch fully closed, so the connection can pivot without binding. The safety chains are then crossed under the drawbar and attached. An eye that rides on top, hangs below, or sits at an angle is not properly seated.

Question 29Coupling and Uncoupling Multiple Trailers

Why are the dolly's safety chains crossed under the drawbar before you attach them to the trailer?

  1. To keep the chains clear of the dolly's air lines
  2. To keep the chains from dragging on the ground
  3. To shorten the chains so they fit the trailer frame
  4. To allow the dolly to turn without the chains binding, and to catch the drawbar if it comes off the hook Correct answer.

Explanation

Crossing the chains under the drawbar forms a cradle that supports the drawbar if the pintle connection fails. The crossed arrangement also lets the dolly pivot in turns without the chains pulling tight and binding. Chains that are not crossed can bind in turns and will not catch the drawbar.

Question 30Coupling and Uncoupling Multiple Trailers

When coupling the second trailer to a dolly, what is the correct order for securing the connection?

  1. Back under the trailer, close the fifth wheel jaws, then check the coupling by pulling gently Correct answer.
  2. Back under the trailer and connect the air lines before the jaws are closed
  3. Close the jaws first, then back under the trailer, then connect the air lines
  4. Connect the air lines first, then back under the trailer and close the jaws

Explanation

You back the dolly under the trailer until the kingpin enters the fifth wheel, then close the jaws and confirm the lock. A gentle pull test with the trailer brakes set verifies the jaws actually captured the kingpin. Air lines are connected after the mechanical coupling is secure.

Question 31Coupling and Uncoupling Multiple Trailers

During a pull test after coupling a trailer to the dolly, the trailer moves rearward with the dolly instead of holding. What does this indicate?

  1. The dolly's landing gear is still down
  2. The trailer's spring brakes are working correctly
  3. The fifth wheel jaws have not locked around the kingpin Correct answer.
  4. The air lines are crossed

Explanation

A pull test is done with the trailer brakes set; the trailer should resist the pull. If it rolls with the dolly, the kingpin is not captured and the jaws are not locked. You must not drive until the coupling is corrected and rechecked.

Question 32Coupling and Uncoupling Multiple Trailers

What is the proper way to check that a fifth wheel has locked onto a kingpin after coupling?

  1. Get under the trailer and visually confirm the jaws are closed around the kingpin, then do a pull test Correct answer.
  2. Tug on the air lines to feel resistance
  3. Look at the release handle from the cab mirror
  4. Pull the release handle outward and listen for a click

Explanation

Visual confirmation that the jaws are closed around the kingpin, plus a pull test with the trailer brakes set, is the reliable check. The release handle position alone can be misleading. You should not rely on sound or on tugging lines to confirm a mechanical lock.

Question 33Coupling and Uncoupling Multiple Trailers

When uncoupling a set of doubles, which trailer's air lines and electrical cord should be disconnected first?

  1. The tractor's lines, before any trailer is touched
  2. Both trailers' lines at the same time
  3. The first trailer's, while the rear trailer is still connected
  4. The rear trailer's, after its brakes are set and the connection is otherwise secured Correct answer.

Explanation

Uncoupling proceeds from the rear forward. After the rear trailer is secured with its brakes set and landing gear down, its lines are disconnected before it is separated from the dolly. Handling the first trailer or the tractor first leaves the rear trailer unsecured.

Question 34Coupling and Uncoupling Multiple Trailers

You are backing the tractor under the first trailer of a doubles set. The trailer's kingpin is too low to enter the fifth wheel. What should you do?

  1. Raise the trailer with its landing gear until the kingpin is at fifth wheel height Correct answer.
  2. Lower the fifth wheel on the tractor
  3. Back harder so the fifth wheel rides up over the kingpin
  4. Drive forward and try again without changing anything

Explanation

A kingpin that is too low will strike the fifth wheel instead of entering it. Adjust the trailer height with the landing gear so the kingpin aligns with the fifth wheel opening. Forcing the tractor back can damage the fifth wheel and the kingpin.

Question 35Coupling and Uncoupling Multiple Trailers

What is the purpose of the trailer protection valve or spring brake priority system on a doubles combination?

  1. To keep the trailer brakes from releasing until enough air pressure is available, protecting against a runaway Correct answer.
  2. To increase air pressure to the rear trailer
  3. To sound an alarm when the trailer is uncoupled
  4. To lock the dolly's fifth wheel

Explanation

The protection system keeps the trailer spring brakes applied until air pressure is sufficient to release them safely. This prevents a trailer from rolling free when pressure is low or lines are disconnected. Its job is protection, not boosting pressure or locking the fifth wheel.

Question 36Coupling and Uncoupling Multiple Trailers

When you apply the trailer hand valve during a brake check on a doubles combination, what should happen?

  1. The dolly brakes release while the trailer brakes apply
  2. The trailer brakes apply while the tractor brakes stay released
  3. Only the tractor brakes apply
  4. All trailer brakes apply and the combination should hold Correct answer.

Explanation

The hand valve supplies air to the trailer brakes, so all trailer brakes, including the dolly's, should apply and hold the combination. The tractor brakes are not applied by the hand valve. If the trailers do not hold, the air system or connections need attention before you drive.

Question 37Coupling and Uncoupling Multiple Trailers

After coupling a set of doubles, you find the dolly's air lines are connected but the trailer brakes do not release when you charge the system. What is a likely cause?

  1. The dolly's supply line is connected to the trailer's service gladhand Correct answer.
  2. The safety chains are too tight
  3. The landing gear is still down
  4. The dolly's fifth wheel is not locked

Explanation

Supply and service gladhands must be matched correctly; swapping them prevents proper charging and brake release. The supply line charges the system, and the service line carries the brake signal. If they are crossed, the brakes may stay applied or behave erratically.

Question 38Coupling and Uncoupling Multiple Trailers

Why should you chock the wheels of the rear trailer before uncoupling it from the dolly?

  1. To keep the air lines from dragging
  2. To keep the trailer from rolling if its spring brakes release or fail Correct answer.
  3. To align the kingpin with the dolly fifth wheel
  4. To make the landing gear easier to crank

Explanation

Chocking the rear trailer's wheels provides a mechanical backup if the spring brakes release or fail while the trailer is disconnected. A disconnected trailer with only air-applied brakes is not fully secure. Chocks hold the trailer in place during the uncoupling process.

Question 39Coupling and Uncoupling Multiple Trailers

What is the correct way to handle the gladhands and electrical cord after separating a trailer in a doubles set?

  1. Leave them hanging so they are easy to find
  2. Tie them to the dolly frame
  3. Hang them on the dummy couplers or secure them so they do not drag or contact the ground Correct answer.
  4. Coil them around the landing gear crank

Explanation

Gladhands should be placed on dummy couplers and the electrical cord secured so neither drags or gets crushed. Lines left hanging can be damaged by the road or caught in moving parts. Coiling them around the landing gear crank interferes with its use.

Question 40Coupling and Uncoupling Multiple Trailers

You are coupling a second trailer to a dolly on uneven ground. What should you check before backing under?

  1. That the safety chains are already attached
  2. That the dolly is level and aligned with the trailer's kingpin, with the trailer secured Correct answer.
  3. That the trailer is pointed downhill
  4. That the dolly's landing gear is raised

Explanation

On uneven ground, the dolly can shift or the trailer can roll, so both must be secured and aligned before you back under. A level dolly and aligned kingpin reduce the chance of a mis-coupling or jackknife. Chains are attached after the drawbar is seated, not before coupling the trailer.

Question 41Inspection of Doubles/Triples Vehicles and Converter Dollies

Before a trip, what is the most important reason to check that the converter dolly's pintle hook is fully closed and latched on the lead trailer's drawbar eye?

  1. An unlatched coupling can separate while driving and let the dolly and rear trailer break away Correct answer.
  2. It keeps the dolly's spring brakes released during normal driving
  3. It prevents the dolly tires from wearing unevenly on curves
  4. It keeps the dolly's electrical cable from dragging on the ground

Explanation

The pintle hook is the primary mechanical link between the dolly and the lead trailer. If it is not fully closed and latched, the coupling can open under load or over bumps, and the dolly with its trailer can separate from the combination. A visual check plus a tug test confirms the latch is seated.

Question 42Inspection of Doubles/Triples Vehicles and Converter Dollies

When you inspect the air lines between the lead trailer and the converter dolly, which condition requires the vehicle to be placed out of service until corrected?

  1. A line that is a few inches longer than needed
  2. A line that is routed through a protective spring wrap
  3. A line with a small amount of dust on the coupler gladhand
  4. A line with a chafed spot that has worn through the outer cover to the reinforcement Correct answer.

Explanation

Air lines must be sound because a failure causes a loss of trailer brakes or an uncontrolled trailer. Damage that reaches the reinforcement or cord means the line is structurally weakened and must be replaced. Dust or extra length does not affect the integrity of the line.

Question 43Inspection of Doubles/Triples Vehicles and Converter Dollies

During a walk-around inspection of a double, you find the rear trailer's emergency (supply) gladhand connected but the service gladhand hanging loose. What happens when the driver releases the parking brakes?

  1. The rear trailer brakes release normally but the trailer has no brakes at all
  2. The rear trailer brakes stay applied and the combination cannot move normally Correct answer.
  3. The dolly's brakes apply automatically to compensate
  4. Only the rear trailer's spring brakes release; service brakes remain functional

Explanation

The emergency/supply line charges the trailer reservoirs and releases the spring brakes. The service line is what actually delivers application air when the driver brakes. With the service line disconnected, the rear trailer cannot be controlled by the foot valve, so the combination must not be driven until it is connected.

Question 44Inspection of Doubles/Triples Vehicles and Converter Dollies

What is the correct order for uncoupling a set of doubles after parking on level ground?

  1. Release the dolly from the lead trailer, then unhook the rear trailer, then lower the dolly landing gear
  2. Lower the dolly landing gear, release the dolly from the lead trailer, then release the rear trailer from the dolly
  3. Chock the rear trailer, disconnect the air lines, then release both couplings at once
  4. Unhook the rear trailer from the dolly, then lower the dolly landing gear and release the dolly from the lead trailer Correct answer.

Explanation

The rear trailer is separated from the dolly first, then the dolly is supported on its landing gear before it is released from the lead trailer. This keeps the dolly supported and controlled at every step. Releasing the dolly from the lead trailer before it is supported lets it drop.

Question 45Inspection of Doubles/Triples Vehicles and Converter Dollies

When coupling a converter dolly to a lead trailer, what does a proper tug test confirm?

  1. That the dolly's landing gear is fully retracted
  2. That the electrical cable is plugged into the correct socket
  3. That the pintle hook has latched around the drawbar eye and will not slip off Correct answer.
  4. That the dolly's air tanks are fully charged

Explanation

After backing the dolly under the lead trailer's drawbar, you close the pintle latch and pull forward gently against the trailer brakes. If the coupling is not seated, the dolly will pull out. This verifies the mechanical connection before you drive.

Question 46Inspection of Doubles/Triples Vehicles and Converter Dollies

You are inspecting the dolly's landing gear before a trip. Which finding means the dolly must not be used?

  1. The landing gear foot has surface rust
  2. The landing gear leg is bent so the dolly frame sits noticeably out of level Correct answer.
  3. The crank handle is stored in its clip on the dolly frame
  4. The landing gear has a small amount of grease on the screw

Explanation

A bent landing gear leg means the dolly cannot be supported properly and may collapse or tip when uncoupled. That is a structural defect and the unit must be taken out of service. Cosmetic rust, grease, and a properly stowed crank are normal.

Question 47Inspection of Doubles/Triples Vehicles and Converter Dollies

What is the purpose of the converter dolly's spring brakes?

  1. To provide extra braking force during hard stops on downgrades
  2. To hold the dolly still only while the driver is coupling
  3. To apply automatically if air pressure is lost, stopping the dolly and its trailer Correct answer.
  4. To keep the dolly tires from rolling when the lead trailer is loaded

Explanation

Spring brakes are held off by air pressure and apply when supply pressure drops, such as during a breakaway or major leak. Because the dolly carries the rear trailer's air supply, its spring brakes are what bring that trailer to a stop if the connection fails.

Question 48Inspection of Doubles/Triples Vehicles and Converter Dollies

During your pre-trip inspection you notice the dolly's slack adjusters move about two inches at the pushrod before the brakes apply. What should you do?

  1. Reduce speed and avoid hard braking for the trip
  2. Continue the trip and note it for the next service interval
  3. Pump the brakes several times to take up the slack
  4. Adjust the slack adjusters or have them repaired before driving Correct answer.

Explanation

Excessive pushrod travel means the brakes are out of adjustment and will not apply fully. The slack adjusters must be adjusted or the brake system repaired before the vehicle is driven. Pumping the brakes does not correct mechanical slack.

Question 49Inspection of Doubles/Triples Vehicles and Converter Dollies

How should the safety chains on a converter dolly be rigged to the lead trailer?

  1. Hooked to the lead trailer frame with enough slack to allow full turns but short enough to catch the drawbar if it separates Correct answer.
  2. Wrapped around the pintle hook and hooked back onto themselves
  3. Left unhooked because the pintle hook is the primary coupling
  4. Crossed under the drawbar and hooked to the same point on both sides

Explanation

Safety chains are a backup that must catch the dolly if the pintle coupling fails. They should be attached to a solid point on the lead trailer with enough slack for turns, but not so much slack that the drawbar hits the ground before the chains take hold.

Question 50Inspection of Doubles/Triples Vehicles and Converter Dollies

Which statement best describes the correct routing of the dolly's electrical cable?

  1. It should be taped to the air lines to keep the bundle together
  2. It should be supported so it does not drag, chafe, or contact the exhaust or moving parts Correct answer.
  3. It should hang loose so it can swing freely with the trailer
  4. It should be looped over the drawbar and left there

Explanation

The electrical cable must be supported and kept clear of the ground, hot surfaces, and moving parts. Dragging or chafing damages the insulation and causes lighting failures. Taping it to air lines or leaving it looped over the drawbar can cause binding or damage.