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Ohio CDL Doubles and Triples Endorsement Test study materials
Ohio CDL Doubles and Triples Endorsement Test study resources

Ohio CDL Doubles and Triples Endorsement Test practice questions

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Question 1Coupling and Uncoupling Twin Trailers

When coupling the second trailer to a set of doubles, what is the first step you should take before backing the converter dolly under the lead trailer's rear apron?

  1. Release the tractor parking brake and roll forward slightly
  2. Chock the trailer wheels and check that the dolly is at the correct height Correct answer.
  3. Connect the electrical cord between the two trailers
  4. Lower the landing gear on the lead trailer to the ground

Explanation

Secure the equipment before you place any part of your body or the dolly beneath a trailer. Chocking the wheels prevents the trailer from rolling, and matching the dolly height to the apron avoids ramming the kingpin. Only after these checks should you back the dolly into position.

Question 2Coupling and Uncoupling Twin Trailers

On a converter dolly, what is the purpose of the locking mechanism that engages the lead trailer's kingpin?

  1. It locks the dolly's wheels so the dolly cannot roll during coupling
  2. It holds the dolly's fifth wheel plate closed around the kingpin so the dolly cannot separate from the lead trailer Correct answer.
  3. It secures the electrical cord to the dolly frame
  4. It holds the rear trailer's landing gear in the raised position

Explanation

The dolly's upper fifth wheel must latch around the kingpin of the lead trailer, exactly as a tractor's fifth wheel latches around a trailer kingpin. If the jaws are not fully closed, the dolly can separate from the lead trailer while moving. A visual and physical tug test confirms the latch is secure.

Question 3Coupling and Uncoupling Twin Trailers

After backing the converter dolly under the lead trailer and hearing the fifth wheel latch, what should you do before connecting the air lines?

  1. Lower the lead trailer's landing gear
  2. Remove the chocks from the rear trailer only
  3. Pull the dolly forward gently against the trailer with the trailer brakes set to test the latch Correct answer.
  4. Immediately release the dolly parking brake and drive away

Explanation

A tug test with the trailer brakes set proves the fifth wheel jaws have closed around the kingpin. If the dolly pulls away from the trailer instead of pulling against it, the coupling has failed and must be corrected. This test is done before air lines are connected so a failed coupling cannot cause a runaway.

Question 4Coupling and Uncoupling Twin Trailers

Which air line connection supplies the emergency (supply) air that charges the rear trailer's reservoirs on a double-trailer combination?

  1. The electrical cord with the seven-pin connector
  2. The service line, usually color-coded blue
  3. The trailer light cable routed through the dolly
  4. The emergency line, usually color-coded red Correct answer.

Explanation

The emergency line carries the constant supply of air that charges the trailer reservoirs and triggers emergency braking if the line separates. The service line carries the air that applies the brakes when the driver presses the pedal. Confusing the two lines causes brake failure or dragging brakes.

Question 5Coupling and Uncoupling Twin Trailers

When uncoupling a set of doubles, why should you close the shut-off valves on the lead trailer before disconnecting the air lines to the dolly?

  1. To prevent air from escaping and to keep the dolly and rear trailer brakes from releasing unexpectedly Correct answer.
  2. To test whether the dolly's relay valve is functioning
  3. To allow the dolly's spring brakes to be manually caged
  4. To drain the dolly's air tanks completely before storage

Explanation

Closing the shut-off valves traps air in the lines and prevents the sudden loss of pressure that would release spring brakes or trigger unwanted emergency braking. It also protects you from whipping air lines when the couplers are separated. Only after the valves are closed should you disconnect the glad hands.

Question 6Coupling and Uncoupling Twin Trailers

What is the correct order for uncoupling the rear trailer from a set of doubles?

  1. Close the shut-off valves, disconnect the air lines and electrical cord, lower the landing gear, then pull the dolly clear Correct answer.
  2. Pull the dolly clear, lower the landing gear, then disconnect the air lines
  3. Disconnect the electrical cord, pull the dolly clear, then close the shut-off valves
  4. Lower the landing gear, pull the dolly clear, then disconnect the air lines

Explanation

You must secure the air supply and separate the connections before the trailer is left standing on its own. Lowering the landing gear to the ground supports the trailer before the dolly is withdrawn. Pulling the dolly clear before these steps would leave the trailer unsupported and the lines stretched or torn.

Question 7Coupling and Uncoupling Twin Trailers

You are coupling a set of triples. Which trailer should be coupled to the tractor first?

  1. The lead trailer, followed by the middle trailer and then the rear trailer Correct answer.
  2. Any trailer, because the order does not affect stability
  3. The middle trailer, followed by the lead and rear trailers
  4. The rear trailer, followed by the middle trailer and then the lead trailer

Explanation

Coupling always proceeds from the tractor rearward: the lead trailer goes on the tractor, then the middle trailer on the lead's dolly, then the rear trailer on the middle's dolly. Working rearward keeps each new unit supported by the one ahead of it. Reversing the order leaves unsupported trailers and makes alignment impossible.

Question 8Coupling and Uncoupling Twin Trailers

Before backing the tractor under the lead trailer of a doubles set, what should you check about the fifth wheel?

  1. That the slider is locked in the forward position
  2. That the jaws are closed and the wheel is dry
  3. That the safety latch is wired shut
  4. That the jaws are open, the wheel is greased, and the height matches the trailer apron Correct answer.

Explanation

The fifth wheel jaws must be open to accept the kingpin, and the plate must be lubricated so the trailer slides and pivots correctly. The tractor and trailer heights must match so the kingpin enters the throat rather than striking the plate. A closed jaw or dry plate causes failed couplings or steering difficulty.

Question 9Coupling and Uncoupling Twin Trailers

When you connect the electrical cord from the dolly to the rear trailer, what should you check immediately afterward?

  1. That the cord is supported so it will not drag or chafe and that the rear trailer lights work Correct answer.
  2. That the cord is wrapped around the dolly's air lines
  3. That the cord is long enough to reach the tractor cab
  4. That the cord is disconnected from the dolly receptacle

Explanation

A cord that drags on the road will wear through and cause lighting or ABS failures. After connecting, test the rear trailer's lights and ABS indicator to confirm the circuit is live. Supporting the cord with hangers keeps it clear of moving parts and the road surface.

Question 10Coupling and Uncoupling Twin Trailers

What is the main reason a converter dolly is used in a doubles or triples combination?

  1. It raises the rear trailer's landing gear automatically
  2. It increases the braking capacity of the rear trailer
  3. It provides a fifth wheel and axle that let one trailer tow another Correct answer.
  4. It supplies electrical power to the rear trailer

Explanation

A converter dolly is a small axle assembly with a fifth wheel that converts a trailer into a towing unit. It carries the front of the towed trailer and provides the pivot point between trailers. Without it, one trailer could not tow another safely.

Question 11Coupling and Uncoupling Twin Trailers

During a pre-trip inspection of a doubles combination, you notice the dolly's safety chains are crossed under the drawbar. Why is this a problem?

  1. Crossed chains reduce air pressure in the dolly's brake chambers
  2. Crossed chains are required by law and should be left as they are
  3. Crossed chains improve the dolly's turning radius
  4. Crossed chains can bind and prevent proper articulation, and they may not hold if the coupling fails Correct answer.

Explanation

Safety chains should be rigged so they do not bind the dolly's movement but still catch the assembly if the coupling fails. Crossing them under the drawbar can restrict articulation and cause the chains to snap under stress. Inspect and correct chain routing before moving.

Question 12Coupling and Uncoupling Twin Trailers

When backing a set of doubles, what happens if you turn the steering wheel too sharply?

  1. The trailers can jackknife or the dolly can be forced out of alignment Correct answer.
  2. The dolly's brakes automatically release
  3. The rear trailer tracks perfectly behind the lead trailer
  4. The trailer lights flash as a warning

Explanation

Doubles respond slowly to steering input and amplify sharp corrections. Oversteering can fold the combination or push the dolly sideways, damaging the coupling. Use small, smooth corrections and pull forward to realign when needed.

Question 13Coupling and Uncoupling Twin Trailers

What should you do if the dolly's fifth wheel jaws fail to latch during coupling?

  1. Drive slowly and let the weight of the trailer seat the jaws
  2. Pull forward, check the jaw mechanism and kingpin, and realign before trying again Correct answer.
  3. Force the jaws closed with a pry bar while the dolly is under the trailer
  4. Leave the jaws open and rely on the safety chains

Explanation

A jaw that will not latch usually means misalignment, a damaged jaw, or a kingpin problem. Pull forward to inspect and correct the cause, then realign and try again. Forcing the jaws or driving with them open risks dropping the trailer.

Question 14Coupling and Uncoupling Twin Trailers

How should the landing gear on a trailer be positioned before a converter dolly is backed underneath it?

  1. Removed entirely to avoid interference
  2. Lowered fully to the ground to stabilize the trailer
  3. Raised high enough that the trailer apron clears the dolly's fifth wheel Correct answer.
  4. Set at the same height as the dolly's frame rails

Explanation

The landing gear must lift the trailer apron above the dolly's fifth wheel so the dolly can slide under and the kingpin can enter the throat. If the gear is too low, the dolly strikes the apron; if too high, the kingpin may not engage. Adjust the gear to match the dolly height before backing.

Question 15Coupling and Uncoupling Twin Trailers

What is the purpose of the shut-off valves located on the lead trailer's air lines to the dolly?

  1. They regulate the pressure applied to the rear trailer's brakes during normal driving
  2. They isolate the air supply so lines can be connected or disconnected without losing pressure Correct answer.
  3. They control the electrical current to the rear trailer's lights
  4. They automatically drain moisture from the dolly's tanks

Explanation

Shut-off valves let you close off the air supply at the lead trailer so the lines can be handled safely during coupling and uncoupling. They are not a pressure regulator for normal braking. Keeping them closed during line work prevents air loss and unexpected brake release.

Question 16Coupling and Uncoupling Twin Trailers

After coupling a set of doubles, you perform a brake test. What should happen when you apply the foot brake?

  1. Only the lead trailer's brakes should apply
  2. The brakes on both trailers should apply together and hold the combination Correct answer.
  3. Only the rear trailer's brakes should apply
  4. The dolly's brakes should release while the trailer brakes apply

Explanation

A properly connected doubles combination applies all trailer brakes together when the foot brake is pressed. If only one trailer brakes, a line is crossed or disconnected and the combination is unsafe. Test the brakes before every trip.

Question 17Coupling and Uncoupling Twin Trailers

Why must the dolly's air tanks be drained during the pre-trip inspection?

  1. To remove moisture and oil that can freeze or corrode the brake system Correct answer.
  2. To test whether the dolly's tires are properly inflated
  3. To reduce the weight of the dolly for better fuel economy
  4. To make the dolly easier to back under the trailer

Explanation

Moisture and oil collect in air tanks and can freeze in cold weather or damage valves and seals. Draining the dolly tanks during pre-trip removes these contaminants. It also confirms that the drain valves are working.

Question 18Coupling and Uncoupling Twin Trailers

What is the correct way to check that the dolly's kingpin is fully seated in the fifth wheel after coupling?

  1. Hose down the fifth wheel plate with soapy water
  2. Look under the trailer to confirm the jaws are closed around the kingpin and tug test with the trailer brakes set Correct answer.
  3. Kick the dolly's tires and listen for a rattle
  4. Check that the dolly's landing gear is on the ground

Explanation

Visual inspection of the jaws and a tug test are the two reliable checks for a seated kingpin. Listening for rattles or kicking tires does not confirm the jaws have closed. If the jaws are not visibly around the kingpin, the coupling is not safe.

Question 19Coupling and Uncoupling Twin Trailers

When uncoupling the lead trailer from the tractor, why should you lower the landing gear until it touches the ground before releasing the fifth wheel?

  1. To lift the trailer off the fifth wheel for easier release
  2. To align the trailer with the next dolly
  3. To apply the trailer spring brakes
  4. So the trailer is supported when the tractor is pulled out from under it Correct answer.

Explanation

The landing gear must carry the trailer's weight once the tractor leaves. Lowering it to firm contact with the ground before releasing the fifth wheel prevents the trailer from dropping. After the gear is set, release the fifth wheel and pull the tractor clear slowly.

Question 20Coupling and Uncoupling Twin Trailers

You are inspecting a converter dolly before a trip and find a cracked frame weld. What is the correct action?

  1. Load the dolly more heavily to test the weld
  2. Cover the crack with paint and continue the trip
  3. Place the dolly out of service and report the defect before using it Correct answer.
  4. Use the dolly only on short trips

Explanation

A cracked weld on a dolly frame is a structural defect that can lead to a catastrophic failure under load. The dolly must be placed out of service and the defect reported and repaired. Painting over or testing the crack in service risks dropping a trailer on the road.

Question 21Coupling and Uncoupling Twin Trailers

What is the correct sequence for connecting the air lines when coupling a set of doubles?

  1. Connect the service line first, then the emergency line
  2. Connect the emergency (supply) line first, then the service line Correct answer.
  3. Connect both lines at the same time with both hands
  4. Connect the service line only and cap the emergency line

Explanation

Connecting the emergency line first charges the trailer system and sets the spring brakes, so the trailer is held while you connect the service line. Reversing the order can cause the trailer to roll or the lines to whip. Always confirm the lines are secure after connecting.

Question 22Coupling and Uncoupling Twin Trailers

Which of the following best describes the pivot point that allows a set of doubles to turn?

  1. The lead trailer's landing gear
  2. The rear trailer's axle assembly
  3. The dolly's fifth wheel, which lets the towed trailer pivot relative to the lead trailer Correct answer.
  4. The tractor's steering axle only

Explanation

The converter dolly's fifth wheel acts as the articulation point between the lead trailer and the towed trailer. This pivot allows the combination to negotiate turns and corners. Without it, the trailers would be rigidly connected and unable to turn.

Question 23Coupling and Uncoupling Twin Trailers

During a pre-trip inspection, you find the dolly's service line coupler has a worn rubber seal. What should you do?

  1. Ignore it because the emergency line will compensate
  2. Tape over the seal to make it seal tighter
  3. Loosen the coupler to relieve pressure on the seal
  4. Replace the seal before the trip to prevent air loss and brake problems Correct answer.

Explanation

A worn glad hand seal leaks air and can cause slow brake release or failure to build pressure. Replacing the seal is a quick, low-cost fix that prevents a roadside breakdown. Taping or loosening the coupler does not restore a proper seal.

Question 24Coupling and Uncoupling Twin Trailers

Why should you avoid backing a set of doubles farther than necessary?

  1. Backup lights are not required on doubles
  2. The rear trailer's brakes do not work in reverse
  3. The combination is difficult to control in reverse and errors can damage the dollies or trailers Correct answer.
  4. Backing uses more fuel than driving forward

Explanation

Doubles amplify steering input and the dolly pivot points make reversing unpredictable. Long backing maneuvers increase the risk of jackknifing or damaging the coupling. Whenever possible, plan the route so you drive forward and avoid extended backing.

Question 25Coupling and Uncoupling Twin Trailers

When coupling the middle trailer of a set of triples, what must be done with the rear trailer before the middle trailer is moved?

  1. It must be loaded to its maximum weight
  2. It must be coupled to the middle trailer first
  3. It must be uncoupled and left secured on level ground with its wheels chocked Correct answer.
  4. It must have its air lines connected to the tractor

Explanation

Each trailer is coupled in sequence from the tractor rearward, so the rear trailer stays secured and separate until the middle trailer is in place. Leaving it chocked and level prevents rolling and allows clear alignment. Coupling the rear trailer first would defeat the sequence.

Question 26Coupling and Uncoupling Twin Trailers

When uncoupling a set of doubles, what must you do with the dolly's air lines after disconnecting them from the rear trailer?

  1. Let them hang free below the dolly frame so moisture drains out
  2. Connect them together to form a closed loop and leave them hanging
  3. Secure them to the dolly frame so couplers do not drag or collect road debris Correct answer.
  4. Loop them over the rear trailer's landing gear crank for storage

Explanation

Air line couplers that are left dangling can drag on the pavement, be crushed by tires, or fill with dirt and moisture that later damages the brake system. Shutting the dolly supply valves and fastening the lines securely to the dolly keeps the couplers clean and protected until the next coupling.

Question 27Coupling and Uncoupling Twin Trailers

You are preparing to couple a converter dolly to the lead trailer's rear. Which condition must the dolly be in before you back it under the trailer?

  1. The dolly must be aligned at a sharp angle to the trailer for easier reach
  2. The dolly must have its air tanks fully charged and its spring brakes released
  3. The dolly's fifth wheel must be tilted down and the wheels chocked so it cannot roll
  4. The dolly's fifth wheel must be tilted up and the wheels chocked so it cannot roll Correct answer.

Explanation

The fifth wheel ramps on a converter dolly are designed to be tilted upward so the trailer's kingpin rides up the ramps and into the jaws as the dolly is pushed under. Chocking the dolly wheels prevents it from rolling away while you position the trailer over it.

Question 28Coupling and Uncoupling Twin Trailers

While towing triples on the highway, you notice the rear trailer tracking noticeably to one side of the middle trailer. What is the most likely cause you should investigate?

  1. A dolly is misaligned or its pintle hook or drawbar is damaged Correct answer.
  2. The middle trailer's landing gear is only partly raised
  3. The rear trailer's spring brakes are adjusted too tightly
  4. The tractor's fifth wheel is set too far forward for the load

Explanation

Each converter dolly pivots independently, so a bent drawbar, worn pintle hook, or misaligned dolly causes the trailer behind it to track off to one side. This is a mechanical defect that must be corrected before continuing, because poor tracking increases off-tracking and sway.

Question 29Coupling and Uncoupling Twin Trailers

After sliding the lead trailer's kingpin into the tractor's fifth wheel, what confirms the coupling is complete and locked?

  1. A firm pull test with the trailer brakes released and the tractor in gear
  2. A visual check of the jaws plus a tug test with the trailer brakes set Correct answer.
  3. The trailer's landing gear lifting clear of the ground
  4. The sound of the kingpin contacting the fifth wheel plate

Explanation

You must look under the trailer to see that the jaws are closed around the kingpin and then pull against the locked trailer with the trailer brakes set to confirm it will not separate. Both checks together are required before you raise the landing gear or connect the air lines.

Question 30Coupling and Uncoupling Twin Trailers

You must park a set of doubles overnight on a lot with a slight grade. Besides setting the parking brakes, what is the correct practice for the dollies and trailers?

  1. Leave all air lines connected and rely on the spring brakes to hold the combination
  2. Chock the wheels of the rear trailer and the dolly, and close the dolly shut-off valves Correct answer.
  3. Lower the landing gear on every trailer and chock the tractor's drive wheels only
  4. Chock the wheels of at least one trailer in the combination and leave the dolly valves open

Explanation

Chocking prevents a trailer or dolly from rolling if air pressure bleeds off and spring brakes release or leak. Closing the dolly shut-off valves keeps the dolly's air system from leaking down through the disconnected lines, so the brakes stay applied.

Question 31Inspecting Doubles and Triples Combinations

During a pre-trip inspection of a doubles combination, where should you check the coupling between the converter dolly and the rear of the first trailer?

  1. At the glad hands, with the couplers sealed against moisture
  2. At the fifth wheel jaws, with the release handle pushed in
  3. At the pintle hook, with the latch closed and the safety pin in place Correct answer.
  4. At the dolly eye, with the drawbar resting on the frame

Explanation

The converter dolly attaches to the rear of the lead trailer through a pintle hook and eye assembly. The latch must be fully closed over the eye and the safety pin or latch pin engaged so the connection cannot open in service. Fifth wheel jaws are checked where the dolly or tractor couples to a trailer kingpin, not at the lead trailer's rear frame.

Question 32Inspecting Doubles and Triples Combinations

You are checking the air lines on a triple-trailer combination before departure. What should you confirm about the converter dolly's air lines?

  1. They are looped over the dolly frame to keep them off the ground
  2. They are supported so they cannot drag or rub, with no leaks at the couplers Correct answer.
  3. They are taped together with the electrical cord to save time
  4. They are disconnected and capped until the vehicle is moving

Explanation

Air lines must be properly connected, free of leaks, and supported so they do not drag, chafe, or contact moving parts. A leak at a coupler or a line rubbing through can cause a loss of trailer brakes. Bundling air lines with the electrical cord or leaving them disconnected defeats the inspection.

Question 33Inspecting Doubles and Triples Combinations

When inspecting the safety chains on a doubles or triples combination, what condition indicates the chains are acceptable?

  1. Chains are crossed under the coupling and have no broken links or worn hooks Correct answer.
  2. Chains are slack enough to touch the pavement when loaded
  3. Chains are welded to the frame to prevent theft
  4. Chains are replaced by bungee cords for quick hookup

Explanation

Safety chains should be crossed where the design calls for it, attached securely, and free of broken links, stretched links, or worn hooks. They are a secondary restraint if the primary coupling fails. Chains dragging on the pavement or substituted with elastic cords will not hold the trailer.

Question 34Inspecting Doubles and Triples Combinations

How should you check the landing gear on a trailer in a doubles or triples combination during your walk-around inspection?

  1. Confirm the crank handle is removed and stored in the cab
  2. Confirm the gear feet are resting on the dolly platform
  3. Confirm the gear is fully raised, the crank is secured, and the legs are not bent Correct answer.
  4. Confirm the gear is lowered slightly to stabilize the trailer

Explanation

Landing gear must be fully retracted and secured so it cannot drop and strike the road at speed. Bent legs, a loose crank, or missing pins are defects that should keep the combination out of service. Resting gear on a dolly platform or leaving it partly down creates a snag and clearance hazard.

Question 35Inspecting Doubles and Triples Combinations

What is the purpose of the shut-off valves (deadman valves) at the rear of each trailer in a doubles or triples combination?

  1. They allow the air supply to be controlled so lines can be connected or tested without losing system pressure Correct answer.
  2. They drain moisture from the air tanks automatically
  3. They lock the dolly pintle so it cannot rotate
  4. They release air from the tires when the trailer is overloaded

Explanation

Shut-off valves at the rear of a trailer let you close off the air supply before connecting or disconnecting lines, and they are used during leak testing. They have nothing to do with tire pressure, pintle locking, or automatic tank draining. Leaving a valve closed in service can leave downstream trailer brakes inoperative.

Question 36Inspecting Doubles and Triples Combinations

During a pre-trip inspection, you notice the converter dolly is missing one of its safety chains. What is the correct action?

  1. Continue if the trailer brakes are working normally
  2. Continue if you reduce speed and avoid sharp turns
  3. Do not move the combination until the chain is replaced or repaired Correct answer.
  4. Continue if the other chain is attached and the pintle is latched

Explanation

A missing safety chain on the converter dolly is an out-of-service defect because the dolly would have no secondary restraint if the pintle connection failed. Operating with one chain, at reduced speed, or relying on the brakes does not correct the defect. The combination should stay parked until the chain is properly restored.

Question 37Inspecting Doubles and Triples Combinations

In a doubles combination, which trailer's brakes are applied when you use the trailer hand valve (trolley valve)?

  1. The brakes on the trailers connected to the trailer supply circuit Correct answer.
  2. Only the rear trailer's brakes
  3. Only the dolly's brakes
  4. Only the lead trailer's brakes

Explanation

The trailer hand valve applies the service brakes on the trailers it controls through the trailer air circuit, which is why it is used to test trailer brake operation. It does not isolate a single trailer or the dolly. Remember that the hand valve should not be used for parking.

Question 38Inspecting Doubles and Triples Combinations

What should you check on the electrical cord connecting the tractor to a doubles or triples combination?

  1. It is plugged in securely, has no exposed wires, and is supported so it does not drag Correct answer.
  2. It is taped over where insulation is worn through
  3. It is wrapped around the air lines for strain relief
  4. It is left unplugged when the rear trailer lights are not needed

Explanation

The electrical cord must be fully seated in its receptacle, free of cracked insulation or exposed conductors, and supported so it does not drag or chafe. Tape over worn insulation is not a proper repair. Unplugging the cord disables trailer lights and antilock power.

Question 39Inspecting Doubles and Triples Combinations

You are coupling a tractor to the lead trailer of a doubles combination. After backing under the trailer, what should you do before pulling the tractor forward to test the coupling?

  1. Leave the landing gear down and tug with the tractor brakes released
  2. Raise the landing gear fully, then tug gently with the trailer brakes set Correct answer.
  3. Connect the air lines only after the tug test
  4. Lower the landing gear to the ground, then tug with the trailer brakes released

Explanation

After the fifth wheel jaws close on the kingpin, raise the landing gear and perform a tug test with the trailer brakes set to confirm the kingpin is locked. Pulling against set trailer brakes reveals a high-hitch or open-jaw condition. Landing gear left down or brakes released defeats the purpose of the test.

Question 40Inspecting Doubles and Triples Combinations

When backing a tractor under a converter dolly to couple it, why must you approach slowly and squarely?

  1. To avoid striking and bending the dolly frame or missing the kingpin Correct answer.
  2. To prevent the pintle hook from opening
  3. To keep the dolly wheels from rolling forward
  4. To allow the air lines to self-align

Explanation

A converter dolly is relatively light and easy to knock out of alignment, so backing slowly and squarely helps you hit the kingpin and avoids bending the frame or running over components. Speed has no effect on line alignment or pintle latch function. Misalignment is a common cause of dolly damage.

Question 41Inspecting Doubles and Triples Combinations

After coupling the converter dolly to the lead trailer, you notice the pintle hook latch will not close over the dolly eye. What is the safest response?

  1. Wire the latch shut and proceed at reduced speed
  2. Proceed because the eye is still resting in the hook
  3. Treat the coupling as defective and do not move until the latch closes and secures properly Correct answer.
  4. Have someone ride on the dolly to watch the coupling

Explanation

If the pintle latch will not close and secure, the coupling cannot be trusted to stay connected under load. Wiring it shut or relying on the eye resting in the hook does not provide a positive lock. A person riding on the dolly is dangerous and illegal.

Question 42Inspecting Doubles and Triples Combinations

During your walk-around on a triples combination, with the wheels chocked and brakes released, you pull by hand on one trailer's S-cam brake slack adjusters. They move more than about an inch where the pushrods attach. What does this indicate?

  1. The spring brakes are working normally
  2. The air lines are crossed and should be swapped
  3. The trailer is overloaded and should be redistributed
  4. The brakes on that trailer need adjustment or repair before operation Correct answer.

Explanation

Excessive movement during this released-brake, manual free-play check indicates that brake adjustment or repair may be needed. That trailer may not brake effectively, so the brakes should be checked and corrected before operation. The roughly one-inch guideline is not a universal limit for applied pushrod stroke.

Question 43Inspecting Doubles and Triples Combinations

What is the correct order for connecting the air lines between the tractor and the first trailer?

  1. Connect the service line first, then the emergency line
  2. Connect the electrical cord first, then both air lines together
  3. Connect both lines at the same time to equalize pressure
  4. Connect the emergency (supply) line first, then the service line Correct answer.

Explanation

Connecting the emergency or supply line first charges the trailer system and helps set the trailer brakes so the trailer stays put while you attach the service line. Reversing the order can leave the trailer without supply air and cause it to roll. The electrical cord is separate from the air line sequence.

Question 44Inspecting Doubles and Triples Combinations

You are inspecting a doubles combination and notice the converter dolly's wheels are not tracking behind the lead trailer but are offset to one side. What is the most likely cause to investigate?

  1. A closed shut-off valve at the rear of the lead trailer
  2. A bent dolly frame or misaligned axle Correct answer.
  3. A loose electrical cord
  4. Low tire pressure in the tractor steer tires

Explanation

A dolly that tracks offset suggests frame or axle alignment damage, which can cause tire wear and unstable handling. Tire pressure in the tractor steer tires, the electrical cord, and a rear shut-off valve do not change dolly tracking geometry. Alignment defects should be corrected before the combination is operated.

Question 45Inspecting Doubles and Triples Combinations

What should you verify about the frame and crossmembers of each trailer during a pre-trip inspection of a doubles or triples combination?

  1. The crossmembers are removed to save weight
  2. No cracks, bends, or loose or missing fasteners are present Correct answer.
  3. The frame is coated with oil to prevent rust
  4. The frame is painted the same color on every trailer

Explanation

Frame and crossmember integrity carries the load and keeps the trailers aligned, so cracks, bends, and loose or missing fasteners are defects that must be repaired. Paint color has no safety meaning. Removing crossmembers weakens the frame, and oil coatings can hide cracks.

Question 46Inspecting Doubles and Triples Combinations

You are checking the coupling between the first and second trailers in a doubles combination. Which component transfers the towing force from the lead trailer to the dolly?

  1. The landing gear legs
  2. The glad hands and couplers
  3. The pintle hook and dolly eye Correct answer.
  4. The fifth wheel plate and kingpin

Explanation

The pintle hook on the lead trailer engages the dolly eye and transmits the towing load to the converter dolly. The fifth wheel and kingpin are used where a tractor or dolly couples to a trailer. Glad hands carry air and landing gear supports a parked trailer.

Question 47Inspecting Doubles and Triples Combinations

During a pre-trip inspection of a doubles combination, how should you confirm the trailer spring brakes are functioning?

  1. With the trailer supply closed, watch for air to escape the glad hands
  2. With the engine off and the system drained, spin each trailer wheel by hand
  3. With the trailer supply charged and then released, listen for the brakes to set and check that the wheels hold Correct answer.
  4. With the hand valve applied, check that the tractor steer wheels lock

Explanation

Charging the trailer supply and then releasing it should cause the trailer spring brakes to set; you confirm the wheels hold. This verifies both the supply circuit and the emergency braking function. Spinning wheels by hand, looking for leaks at the couplers, or watching the tractor steer wheels does not test trailer spring brake application.

Question 48Inspecting Doubles and Triples Combinations

What is the purpose of the converter dolly's own spring brakes in a doubles or triples combination?

  1. To increase the load carried by the lead trailer
  2. To allow the dolly to be towed without air lines
  3. To keep the pintle hook from rotating during turns
  4. To hold the dolly and trailers if the dolly loses air supply Correct answer.

Explanation

The dolly's spring brakes apply automatically when air supply is lost, helping to stop and hold the combination. They do not increase load capacity, lock the pintle, or permit towing without air lines. Towing without air supply would leave the dolly brakes applied and the combination unbraked.

Question 49Inspecting Doubles and Triples Combinations

You are inspecting a triples combination and find a trailer's air tank drain valve stuck open, leaking air continuously. What should you do?

  1. Drain the remaining tanks to match the leak
  2. Close the valve with tape and continue the trip
  3. Continue because the other trailers have air
  4. Do not dispatch the combination until the drain valve is repaired or replaced Correct answer.

Explanation

A continuously leaking drain valve will deplete the air supply and can cause the spring brakes to apply or reduce braking performance. Taping a valve is not a repair, and the other trailers cannot compensate for a system leak. Draining additional tanks makes the air loss worse.

Question 50Inspecting Doubles and Triples Combinations

During a walk-around of a doubles combination, you notice the electrical cord between the tractor and lead trailer is chafed through to bare wire. Why must this be corrected before departure?

  1. The cord only powers the cab dome light and is optional
  2. Bare conductors can short, causing loss of trailer lights and antilock power Correct answer.
  3. The cord carries brake air and will leak
  4. Bare wire improves the ground connection and is acceptable

Explanation

Exposed conductors can short against the frame, blowing fuses and disabling trailer lights or antilock power, which are required safety systems. Bare wire is never acceptable, and the cord does not power only the dome light or carry air. Chafed cords should be repaired or replaced before the trip.