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Illinois CDL Doubles and Triples study materials
Illinois CDL Doubles and Triples study resources

Illinois CDL Doubles and Triples practice questions

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Question 1Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

During the pre-trip inspection of a double-trailer combination, what should you verify about each glad hand connection?

  1. That the rubber seal is present and undamaged Correct answer.
  2. That the glad hand is tightened with a wrench until it cannot move
  3. That the service line is connected with the red coupler
  4. That the metal coupler is painted the same color as the trailer

Explanation

Glad hand seals keep air from escaping at the coupling point. A missing, cracked, or torn seal can cause air pressure loss and weak or dragging trailer brakes. Check that the seal is in place and that the coupler locks securely by hand.

Question 2Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

What is the main purpose of the safety chains on a converter dolly used in double or triple trailer operation?

  1. To release the dolly brakes during an emergency stop
  2. To support the weight of the rear trailer when parked
  3. To hold the dolly if the pintle hook fails Correct answer.
  4. To carry the electrical current for the trailer lights

Explanation

Safety chains are a backup attachment for the converter dolly. If the pintle hook or coupling fails, the chains should keep the dolly from separating from the towing vehicle. Inspect them for cracks, missing hooks, and secure attachment.

Question 3Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

Before you crawl under a double or triple trailer to inspect brake chambers and air lines, what should you do first?

  1. Leave the engine running so the air pressure stays up
  2. Disconnect the emergency line to release the spring brakes
  3. Have a second person hold the brake pedal down
  4. Set the parking brakes, chock the wheels, and remove the key Correct answer.

Explanation

You must secure the combination against rollaway before going underneath. Set the parking brakes, chock the wheels, and keep the key out of the ignition so no one can start the engine or release the brakes unexpectedly. Never depend on air pressure alone to hold a heavy combination in place.

Question 4Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

With the air system fully charged on a triple-trailer combination and the engine off, what is the maximum allowable air pressure loss in one minute?

  1. 1 psi
  2. 4 psi
  3. 2 psi
  4. 3 psi Correct answer.

Explanation

For a combination vehicle, the air brake leak test allows no more than 3 psi loss in one minute with the engine off and the system fully charged. A single vehicle is allowed only 2 psi in one minute. Any greater loss means you must find and fix the leak before driving.

Question 5Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

When inspecting the spring brakes on the trailers of a double or triple combination, which observation shows they are working properly?

  1. The pushrods stay extended with full air pressure applied
  2. The slack adjusters move freely by hand with the brakes applied
  3. The pushrods extend when air pressure drops Correct answer.
  4. The brake chambers are cool after the engine is shut off

Explanation

Spring brakes are applied by heavy springs when air pressure is released, so the pushrods should extend as pressure drops. When full air pressure is applied, the springs are compressed and the pushrods should retract. This test shows whether the trailer brakes apply and release correctly.

Question 6Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

How should you check that a converter dolly's pintle hook is properly locked before pulling double trailers?

  1. Confirm the latch is closed and the safety pin is engaged Correct answer.
  2. Check that the dolly's landing gear is raised halfway
  3. Spray the hook with lubricant and leave the latch open
  4. Pull the dolly backward by hand until the hook opens

Explanation

The pintle hook must be fully closed with its secondary latch or safety pin engaged so the dolly eye cannot bounce out. Visually confirm the latch position and give the dolly a careful tug test. A partially closed hook can open in service and cause separation.

Question 7Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

What should you check on the electrical cord between the tractor and the first trailer of a double or triple combination?

  1. That it is taped to the trailer frame with no slack
  2. That it is plugged in, untangled, and has slack for turns Correct answer.
  3. That it is wrapped tightly around the air lines for support
  4. That it is disconnected so it cannot short during the inspection

Explanation

The electrical cord must be fully plugged in so the trailer lights work, and it should be free of tangles or chafing. It needs enough slack to stay connected when the combination turns or articulates. A tight cord can pull loose or break, leaving the trailer without lights.

Question 8Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

On the rear trailer of a triple-trailer combination, which inspection item is most critical because it warns following drivers of your presence?

  1. The trailer's front bulkhead
  2. The landing gear crank handle
  3. The rear lights and reflective tape Correct answer.
  4. The converter dolly's pintle hook

Explanation

The rear-most trailer carries the lights, reflectors, and conspicuity tape that following drivers see first. These must be clean, undamaged, and working so the long combination is visible at night and in bad weather. A failed rear light or missing reflective tape makes the triple combination much harder to see.

Question 9Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

During a pre-trip inspection, you find that the red emergency glad hand seal on the second trailer is missing. What is the correct action?

  1. Connect the red line without a seal and rely on the coupler lock
  2. Swap the red and blue lines so the seal is not needed
  3. Plug the red line into the blue glad hand to stop the leak
  4. Replace the seal with a proper glad hand seal before moving Correct answer.

Explanation

A missing emergency glad hand seal allows air to escape and can prevent the trailer brakes from releasing properly or cause brake drag. You must install a proper replacement seal before moving the combination. Do not improvise with tape or cross-connect the air lines.

Question 10Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

After charging the air system on a triple-trailer combination and shutting off the engine, you observe a 4 psi drop in one minute. What should you do?

  1. Increase engine idle to build pressure and then depart
  2. Continue the trip because triple trailers are allowed a 5 psi loss
  3. Release the trailer parking brakes to test for a leak
  4. Find and repair the air leak before driving the combination Correct answer.

Explanation

A combination vehicle may lose no more than 3 psi in one minute during the air leak test. A 4 psi drop exceeds that limit and shows there is a leak somewhere in the tractor, dolly, or trailer air system. You must locate and repair the leak before driving, because poor air pressure can weaken or delay braking.

Question 11Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

During the pre-trip inspection of a triple-trailer combination, which wheels must you check for tread depth, inflation, and damage?

  1. Only the steer axle and the rear trailer axle
  2. Only the tractor drive wheels and first trailer wheels
  3. Only the wheels visible from the driver's side
  4. Every wheel on the combination Correct answer.

Explanation

Every wheel on the tractor, converter dollies, and trailers supports the combination and can develop a defect that affects control or causes a breakdown. Limiting the check to visible wheels or power axles leaves dolly and rear-trailer defects undiscovered. A complete pre-trip inspection covers all wheel positions.

Question 12Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

When inspecting the converter dolly wheels on a double-trailer combination, what should you check about the lug nuts?

  1. That only the outer nut on each wheel is tight
  2. That they are painted the same color as the wheel
  3. For looseness, cracks, missing nuts, or rust trails Correct answer.
  4. That they can be removed by hand

Explanation

Lug nuts must be tight and undamaged, and rust trails can indicate a loose nut or stud. Missing or cracked nuts mean the wheel may separate from the dolly. Hand removal is not a proper tightness check.

Question 13Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

After coupling the second trailer to a converter dolly, what should you confirm about the dolly's fifth wheel?

  1. The kingpin is resting on top of the jaws
  2. The jaws are locked around the kingpin Correct answer.
  3. The release handle is tied open for unloading
  4. The fifth wheel plate is coated with grease

Explanation

A secure fifth wheel connection requires the jaws to close around the trailer kingpin. The release handle and safety latch must also be in the locked position so the trailer cannot separate. A high hook or open jaw is a serious coupling defect.

Question 14Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

What should you look for when inspecting the air lines that run from the converter dolly to the trailers on a triple-trailer combination?

  1. That they are routed through the exhaust to stay warm
  2. That they are free of cracks and chafing Correct answer.
  3. That they are the same length as the electrical cord
  4. That they are taped to the frame with no slack

Explanation

Air lines carry pressure for service and emergency braking, so cracks, chafing, and worn spots can lead to leaks or sudden brake loss. Lines should be supported without being so tight that they pull apart during turns. Damaged lines must be repaired before operation.

Question 15Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

During pre-trip inspection of a double-trailer combination, what should you check on the suspension of each trailer?

  1. For broken springs, loose U-bolts, and air bag leaks Correct answer.
  2. That only the lead trailer has an air suspension
  3. That all springs are painted and free of grease
  4. That the axle is welded to the spring hanger

Explanation

Suspension defects such as broken springs, loose U-bolts, cracked hangers, or leaking air bags can cause poor tracking, tire wear, or loss of control. Every trailer and dolly suspension must be inspected. Cosmetic conditions are not the concern.

Question 16Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

When inspecting the converter dolly frame on a triple-trailer combination, where should you pay particular attention for cracks or bends?

  1. At the center of the mud flap
  2. At the drawbar and its welds Correct answer.
  3. At the license plate bracket
  4. At the top of the air tank

Explanation

The drawbar and its welded joints carry the pulling and braking forces between the lead trailer and the dolly. Cracks or bends in that area can lead to separation of the dolly or trailers. The entire frame should be checked, with extra attention to high-stress connections.

Question 17Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

What is the correct pre-trip check for the rear trailer's mud flaps on a triple-trailer combination?

  1. They should cover only the outer tire
  2. They should hang so they touch the road
  3. They should be removed to save weight
  4. They should be securely mounted and not dragging Correct answer.

Explanation

Mud flaps must be securely attached, in good condition, and positioned so they do not drag on the road. They help reduce spray and debris thrown toward following traffic. A loose or dragging flap is a defect to correct before departure.

Question 18Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

During a pre-trip inspection of a double-trailer combination, the rear trailer's ABS warning lamp stays on after the ignition is turned on. What is the best action?

  1. Ignore the lamp if the trailer brakes feel normal
  2. Continue because the tractor ABS will cover it
  3. Do not dispatch until the ABS fault is repaired Correct answer.
  4. Disconnect the ABS cord and use the brakes

Explanation

A steady ABS warning lamp indicates a fault in the trailer's antilock brake system. The trailer may still have brakes, but it may lose ABS function, which can affect stability during hard braking. The fault should be repaired before the combination is dispatched.

Question 19Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

While inspecting a triple-trailer combination, you find a small air leak at a fitting on the second dolly's service line. What should you do?

  1. Wrap the fitting with tape and continue if pressure builds
  2. Continue because a small leak will seal when warm
  3. Close the trailer air supply valve and use only tractor brakes
  4. Repair or replace the leaking fitting before operating Correct answer.

Explanation

Any air leak in a service line can worsen and reduce the trailer's braking performance. A leaking fitting must be repaired or replaced, not masked with tape or ignored. Operating with a known air leak is unsafe and can lead to brake failure.

Question 20Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

How should you test the tractor protection valve before pulling double trailers?

  1. Disconnect all trailer air lines and drive slowly
  2. Pump the brake pedal until the warning sounds
  3. Close the trailer air supply valve and check that pressure holds Correct answer.
  4. Open the trailer air supply valve and listen for a hiss

Explanation

With the system charged, closing the trailer air supply valve should apply the trailer brakes and the tractor protection valve should prevent tractor air from escaping. A continuous pressure drop indicates a leak or faulty valve. This test confirms the tractor can protect its air supply if a trailer separates.

Question 21Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

During the pre-trip inspection of a triple-trailer combination, what should you verify about the rear impact guard on the last trailer?

  1. It is securely mounted, undamaged, and at the required height above the road. Correct answer.
  2. It is removed from the last trailer to save weight on the combination.
  3. It is painted the same color as the trailer frame and running lights.
  4. It is hinged upward so it will not drag when the trailer is empty.

Explanation

The rear impact guard must be firmly attached, free of cracks or bends, and at the height required for the trailer. A loose or damaged guard may not protect a following vehicle in a rear-end crash.

Question 22Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

For a double-trailer combination, what should you confirm about the emergency warning devices during the pre-trip inspection?

  1. A flashlight is tied to the converter dolly frame.
  2. Two flares are permanently mounted on the rear trailer bumper.
  3. One red flag is stored under the driver's seat for use at night.
  4. Three reflective triangles are present, clean, and undamaged. Correct answer.

Explanation

A commercial vehicle must carry at least three warning devices, typically reflective triangles, and they must be in usable condition. During pre-trip, check that all three are present, clean, and not broken.

Question 23Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

During the pre-trip inspection of a triple-trailer combination, what should you check about the reflective tape and reflectors on each trailer?

  1. They are present, securely attached, and not faded, torn, or missing. Correct answer.
  2. They are replaced with white tape on the rear trailer only.
  3. They are covered with mud to reduce glare from following vehicles.
  4. They are removed from the middle trailer to avoid confusing other drivers.

Explanation

Reflective tape and reflectors help other drivers see the combination at night and must be intact on each trailer. Look for missing, faded, torn, or poorly attached material during the walk-around.

Question 24Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

When inspecting a converter dolly before pulling double trailers, what should you check about its landing gear or support legs?

  1. They are fully raised, locked up, and free of bent braces. Correct answer.
  2. They are coated with oil instead of wheel-bearing grease.
  3. They are wired into the trailer's stop lamp circuit.
  4. They are lowered until they touch the road while the combination is towed.

Explanation

Dolly support legs must be fully raised and secured before towing so they cannot drag or strike the road. Check the pins, braces, and locking mechanism for damage or wear.

Question 25Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

While inspecting the trailer brakes on a double-trailer combination, what should you check about the brake pushrods and slack adjusters?

  1. The pushrod boot is packed with grease to stop all pushrod travel and seal the chamber.
  2. Pushrod travel is within limits, and the slack adjuster is not cracked or loose. Correct answer.
  3. The pushrod is fully extended while the brakes are released.
  4. The slack adjuster is welded to the brake chamber to prevent any movement during operation.

Explanation

Brake pushrod travel must be within the allowed limit, and the slack adjuster must be intact and connected. Excess travel or a damaged adjuster can leave the trailer brakes weak or inoperative.

Question 26Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

During the pre-trip inspection of a double-trailer combination, why should you check the clearance between the tires and the trailer body or between trailers?

  1. To verify that the mud flaps have been removed before travel on the highway.
  2. To confirm the tires are touching the frame for stability during highway driving.
  3. To ensure tires will not rub or contact the combination on turns or uneven ground. Correct answer.
  4. To ensure the tires are inflated to the maximum sidewall pressure shown on the tire.

Explanation

In a multi-trailer combination, tires can contact trailer bodies, fenders, or other trailers during turns or uneven ground if clearance is too small. Check for rub marks or close gaps that could cause tire damage or loss of control.

Question 27Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

What should you do with the air tank drains on a converter dolly during the pre-trip inspection?

  1. Leave them open so the tank cannot build pressure during the trip.
  2. Fill them with oil to lubricate the air system and valves.
  3. Seal them permanently with epoxy to prevent any air loss.
  4. Open them to drain moisture, then close and check for leaks. Correct answer.

Explanation

Air tank drains remove moisture that can freeze or corrode the air system. After draining, close each drain tightly and check that it does not leak.

Question 28Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

After coupling a trailer to a converter dolly, how should you perform the tug test before completing the pre-trip inspection?

  1. Lift the trailer with the landing gear while the tractor transmission is in gear.
  2. Have a helper watch while you accelerate hard to 20 mph.
  3. Set the trailer brakes, pull gently against the coupling, and check for separation. Correct answer.
  4. Release all brakes and coast downhill to see if the trailer stays attached securely.

Explanation

The tug test confirms that the fifth-wheel jaws have closed around the kingpin. With the trailer brakes set, pull gently against the coupling and watch for any separation or movement.

Question 29Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

During the pre-trip inspection of a triple-trailer combination, you find a crack in the converter dolly's fifth-wheel mounting plate. What is the correct action?

  1. Shift the crack to the underside by rotating the fifth wheel.
  2. Tighten the mounting bolts and cover the crack with grease.
  3. Do not move the combination until the plate is repaired or replaced. Correct answer.
  4. Continue the trip if the crack is shorter than the width of the mounting plate.

Explanation

A cracked fifth-wheel mounting plate can fail and allow the trailer to separate from the dolly. The combination must be placed out of service until the defect is properly repaired.

Question 30Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

During the pre-trip inspection of a triple-trailer combination, the tractor air gauge reads normal, but the rear trailer's spring brakes will not release. Which check is most appropriate first?

  1. Remove the rear trailer's spring brake chambers and cage them by hand before driving.
  2. Increase engine speed to maximum to force air past the trailer valve.
  3. Open the rear trailer's air tank drain and leave it open while you check the system.
  4. Check that the rear trailer's emergency shut-off valve is open. Correct answer.

Explanation

If the tractor has normal pressure but the rear trailer will not release, the supply air may not be reaching that trailer. Check that the emergency glad hand valve is open and that the line is not kinked, closed, or disconnected.

Question 31Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

Before pulling double trailers, what should you confirm about the tractor's fifth-wheel release arm during the pre-trip inspection?

  1. It is fully engaged in the safety latch and secured. Correct answer.
  2. It is greased and left resting on the trailer apron.
  3. It is tied back so the jaws stay open.
  4. It is removed to prevent accidental uncoupling.

Explanation

The release arm must be in the locked position with its safety latch engaged; otherwise the fifth-wheel jaws can open and release the kingpin. A secured release arm is part of the coupling-system check before moving doubles.

Question 32Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

During the pre-trip inspection of a double-trailer combination, what should you check about the electrical cord running from the tractor to the first trailer?

  1. It is wrapped tightly around the air lines to keep it off the frame.
  2. It is run over the catwalk so it can rub against the deck.
  3. It is plugged in and routed so it cannot drag or chafe. Correct answer.
  4. It is left unplugged until the trailer lights are tested.

Explanation

The electrical cord must be fully seated in the receptacle and supported so it does not drag, chafe, or pull loose. A loose or damaged cord can cause trailer lights and ABS to fail during the trip.

Question 33Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

When inspecting the rear of the first trailer before coupling a converter dolly for a triple-trailer combination, what should you check about the pintle hook?

  1. The latch is wired open so the drawbar eye can drop into place more easily.
  2. The hook is coated with grease so the latch cannot fully close.
  3. The drawbar eye rests on top of the hook rather than inside it.
  4. The latch locks over the eye and the hook is not cracked or worn. Correct answer.

Explanation

The pintle hook must capture the dolly drawbar eye with the latch closed and secured, and the hook must be free of cracks or heavy wear. If the eye is not fully seated or the latch is open, the dolly can separate from the trailer.

Question 34Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

During the pre-trip inspection of a double-trailer combination, what should you verify about the sliding tandem locking pins on each trailer?

  1. The pins are fully engaged and their retainers are secured. Correct answer.
  2. The pins are removed so the tandem can move freely with the load.
  3. The pins are partly engaged to allow the tandem to shift on curves.
  4. The pins are greased and left hanging loose beside the frame.

Explanation

Sliding tandem locking pins must be fully seated in the frame holes and their retainers secured; otherwise the tandem can shift while driving. Partly engaged or missing pins can damage the trailer and affect handling.

Question 35Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

On the rear trailer of a triple-trailer combination, what should you check about the unused gladhands during the pre-trip inspection?

  1. They are connected to each other with a short loop of air line.
  2. They are left open so air pressure can escape freely when the brakes are applied.
  3. They are taped shut with paper tape so the seals stay dry.
  4. They are covered with dummy couplers or dust caps. Correct answer.

Explanation

Unused gladhands on the rear trailer should have dummy couplers or caps installed to protect the seals from dirt and moisture. Open gladhands can let contaminants in and cause air leaks or brake problems.

Question 36Preventive Maintenance and Pre-Trip Inspection for Double/Triple Trailers

During the pre-trip inspection of a double-trailer combination, you find the converter dolly safety chains are tight with no slack while the rig is straight. Why should you correct this before driving?

  1. Tight chains improve the dolly's ride by holding the drawbar rigid.
  2. Tight chains are required to keep the dolly from rolling when parked.
  3. The chains should be tight so they can carry the trailer's air lines.
  4. The chains need slack so they can allow turns without binding or breaking. Correct answer.

Explanation

Safety chains must have enough slack to let the dolly and trailer articulate in turns; tight chains can bind, stretch, or break. They are a secondary restraint, not a rigid tow bar, so correct slack and attachment are checked before moving.

Question 37Coupling System and Converter Dolly

Before backing the tractor under a semitrailer, the fifth wheel locking jaws must be in which position?

  1. Fully open, with the release handle out Correct answer.
  2. Fully closed and latched
  3. Partially open to receive the kingpin
  4. Removed so the kingpin can pass through

Explanation

The locking jaws must be fully open so the kingpin can slide between them and trip the latch as the tractor backs under the trailer. If the jaws are closed or only partly open, the kingpin cannot enter, the trailer may be pushed backward, and the coupling will not be secure. Confirm the release handle is out and the jaws are open during the walk-around inspection.

Question 38Coupling System and Converter Dolly

What does a converter dolly add to a tractor-semitrailer combination?

  1. A second fifth wheel for another semitrailer Correct answer.
  2. A second engine brake circuit for the rear trailer
  3. A hydraulic lift axle for heavy loads
  4. An extra fuel tank for long-haul routes

Explanation

A converter dolly is a separate axle assembly with its own fifth wheel and a drawbar that attaches to a pintle hook on the first trailer. It lets one tractor pull two or three semitrailers by carrying the kingpin of the next trailer. It does not add engine braking, a lift axle, or fuel capacity.

Question 39Coupling System and Converter Dolly

Which color identifies the emergency (supply) air line in a tractor-trailer system?

  1. Red Correct answer.
  2. Green
  3. Blue
  4. Black

Explanation

Standard glad-hand color coding uses red for the emergency (supply) line and blue for the service line. The emergency line charges the trailer air tanks and controls the spring brakes, so mixing the lines can leave the trailer brakes applied or unreleased. Check colors and couplers before connecting.

Question 40Coupling System and Converter Dolly

After backing under a trailer and hearing the fifth wheel latch, how should you complete the coupling check?

  1. Disconnect the service line and listen for a leak
  2. Tug forward with trailer brakes locked Correct answer.
  3. Lower the landing gear and then drive forward slowly
  4. Release the trailer brakes and drive forward at highway speed

Explanation

With the trailer brakes set, pull forward slowly against them. If the fifth wheel is locked, the tractor will be held back or the trailer will rock; if the tractor moves freely, the jaws are not locked and the coupling must be corrected. Never skip this tug test or rely only on the sound of the latch.

Question 41Coupling System and Converter Dolly

Air will not reach the converter dolly from the first semitrailer. What should you check first?

  1. The fifth wheel release handle
  2. The pintle hook latch
  3. The dolly's landing gear crank
  4. The shut-off valves at the trailer rear Correct answer.

Explanation

The rear of the first trailer has shut-off valves that must be open to feed the converter dolly and the trailer behind it. If they are closed, the dolly's emergency and service lines get no air, and the rear trailer's brakes stay applied or its tanks never charge. Landing gear, pintle latch, and the fifth wheel handle do not control air flow.

Question 42Coupling System and Converter Dolly

When you drop the converter dolly after uncoupling, the dolly landing gear should be:

  1. Left fully retracted so it clears the ground
  2. Lowered only until it touches the rear tires
  3. Removed and stored inside the tractor cab
  4. Cranked down to support the dolly frame Correct answer.

Explanation

The dolly's landing gear carries the weight of the dolly when the tractor no longer supports it, so crank it down until the frame is firmly supported on the ground. Then you can release the pintle hook and pull the first trailer away safely. Leaving the gear retracted lets the dolly tip or drop.

Question 43Coupling System and Converter Dolly

In the cab, what happens when you pull out the trailer air supply (red) knob?

  1. The dolly shut-off valves open automatically
  2. The fifth wheel jaws unlock for uncoupling
  3. The emergency line closes and the trailer spring brakes set Correct answer.
  4. The trailer service brakes are released and it rolls freely downhill

Explanation

The red trailer air supply knob controls the emergency line. Pushing it in charges the trailer system and releases the spring brakes; pulling it out closes the line, which exhausts the trailer supply and applies the spring (parking) brakes. It does not release the service brakes or unlock the fifth wheel.

Question 44Coupling System and Converter Dolly

When securing the converter dolly to the first semitrailer, the safety chains should be:

  1. Attached only to the dolly frame itself
  2. Crossed and hooked to the trailer frame Correct answer.
  3. Wrapped around the pintle hook and tied with wire
  4. Left hanging loose beneath the dolly drawbar

Explanation

Converter dolly safety chains are hooked to the frame of the first trailer and crossed under the drawbar. Crossing them cradles the drawbar if the pintle hook or eye fails, keeping the dolly from dropping to the pavement. Chains left loose, tied, or attached only to the dolly provide no backup.

Question 45Coupling System and Converter Dolly

During your walk-around inspection of a coupled set of doubles, you find the pintle hook latch closed but the safety pin missing. What is the correct action?

  1. Proceed, since the latch spring holds the hook closed
  2. Install a locking pin before moving Correct answer.
  3. Tie the latch down with wire and continue the trip
  4. Remove the latch so the hook can be visually checked

Explanation

The pintle hook's latch must be closed and secured with its locking pin. Without the pin, vibration can let the latch open, the drawbar eye can escape, and the dolly and rear trailer can separate. A spring alone is not a secure lock, and wire or removal of the latch is unsafe.

Question 46Coupling System and Converter Dolly

You back under the second trailer, hear the fifth wheel latch, but see a gap between the fifth wheel and the trailer apron. What does this indicate?

  1. The fifth wheel needs more grease before coupling
  2. The kingpin missed the jaws, so the couple is not secure Correct answer.
  3. The trailer sat too low and the landing gear must be raised
  4. The kingpin is properly seated and the gap is normal

Explanation

After coupling, the fifth wheel and trailer apron should be in firm contact with no visible gap. A gap means the kingpin is riding on top of the jaws or otherwise not locked, so the trailer is not safely coupled. Lower the trailer, recheck the coupling height, and repeat the coupling and tug test.

Question 47Coupling System and Converter Dolly

On a doubles combination, which color identifies the service air line between the tractor and the first semitrailer?

  1. Black
  2. Green
  3. Red
  4. Blue Correct answer.

Explanation

The service air line is blue, and the emergency or supply line is red. Color coding helps prevent crossing the lines when you connect a converter dolly or semitrailer. A crossed service line can keep the dolly's spring brakes applied.

Question 48Coupling System and Converter Dolly

The pintle hook on a converter dolly is designed to couple to which part of the first semitrailer?

  1. The gladhand
  2. The electrical receptacle
  3. The kingpin
  4. The lunette eye Correct answer.

Explanation

A pintle hook opens and closes around a lunette eye, also called a pintle eye, mounted at the rear of the first semitrailer. The kingpin is the vertical pin that locks into a fifth wheel, not into a pintle hook.

Question 49Coupling System and Converter Dolly

When uncoupling a set of doubles, which trailer should you drop first?

  1. Either trailer, as long as the dolly is chocked
  2. Both trailers at the same time
  3. The front semitrailer
  4. The rear semitrailer Correct answer.

Explanation

Drop the rear semitrailer first, then the converter dolly, and finally the front semitrailer. This order keeps the dolly supported and avoids moving a dolly that still has a trailer attached to its fifth wheel.

Question 50Coupling System and Converter Dolly

You cannot pull the fifth wheel release handle to uncouple the second trailer from the converter dolly. What is the best first step?

  1. Back up slightly to relieve pressure Correct answer.
  2. Raise the landing gear before coupling
  3. Drive forward sharply to free the jaws
  4. Disconnect the air lines at the gladhands

Explanation

Pressure from the kingpin against the locking jaws can bind the release handle. Backing the dolly slightly toward the trailer takes pressure off the jaws so the handle can move. Do not force the handle or drive forward with the trailer still coupled.