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IN CDL Combination study materials
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IN CDL Combination practice questions

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Question 1Combination Vehicle Inspection and Coupling/Uncoupling

During a pre-trip inspection of a combination vehicle, where should you check the fifth wheel mounting bolts?

  1. On the underside of the trailer frame rails
  2. On the tractor frame where the fifth wheel plate is mounted Correct answer.
  3. On the trailer landing gear crossmember
  4. On the kingpin mounting plate inside the trailer

Explanation

The fifth wheel is bolted to the tractor frame, so the mounting bolts must be checked where the plate attaches to the frame rails. Loose or missing mounting bolts can let the fifth wheel shift or separate under load, which is a serious coupling failure.

Question 2Combination Vehicle Inspection and Coupling/Uncoupling

When uncoupling a trailer on level ground, what should you do with the landing gear before releasing the fifth wheel?

  1. Raise it slightly so the trailer clears the tractor frame
  2. Leave it fully retracted so the trailer rests on the tractor
  3. Extend it only halfway to save cranking time
  4. Lower it until it firmly contacts the ground and supports the trailer Correct answer.

Explanation

The landing gear must be lowered until it is firmly on the ground and bearing the trailer weight before the fifth wheel is released. Otherwise the trailer front drops when the tractor pulls away, damaging the trailer and possibly the tractor.

Question 3Combination Vehicle Inspection and Coupling/Uncoupling

You are coupling to a trailer and the fifth wheel jaws close around the kingpin. What is the correct next step to verify the connection?

  1. Crank the landing gear up first, then check the jaws
  2. Do a visual check and a tug test, then set the trailer brakes and pull forward Correct answer.
  3. Pull the tractor forward gently while watching the trailer
  4. Release the trailer spring brakes and listen for air leaks

Explanation

After the jaws close, you should visually confirm the jaws are locked around the kingpin, do a tug test against the trailer brakes, and then secure the release handle. This verifies the coupling before you raise the landing gear and drive away.

Question 4Combination Vehicle Inspection and Coupling/Uncoupling

What is the purpose of the safety latch on a fifth wheel release handle?

  1. It adjusts the height of the fifth wheel plate
  2. It holds the kingpin steady while backing
  3. It locks the trailer brakes during coupling
  4. It keeps the release handle from moving and opening the jaws Correct answer.

Explanation

The safety latch secures the release handle so vibration and road shock cannot pull the handle and open the locking jaws. Without it, an uncoupling could occur while the vehicle is moving.

Question 5Combination Vehicle Inspection and Coupling/Uncoupling

Before backing under a trailer to couple, what should you check about the trailer height relative to the fifth wheel?

  1. The trailer should be high enough that the tractor passes completely under the nose
  2. The trailer should be raised so the kingpin clears the fifth wheel by at least a foot
  3. The trailer kingpin plate should be slightly lower than the fifth wheel so the tractor lifts it Correct answer.
  4. The trailer nose should be level with the top of the tractor frame

Explanation

The trailer should be positioned so the kingpin plate is a little lower than the fifth wheel, allowing the plate to ride up the ramps and lock. Too high and the tractor passes under without coupling; too low and you can strike and damage the trailer.

Question 6Combination Vehicle Inspection and Coupling/Uncoupling

Which item is part of the air brake check on a combination vehicle during the pre-trip inspection?

  1. Checking that the trailer spring brakes release and the lines hold pressure Correct answer.
  2. Checking the mud flap clearance
  3. Inspecting the trailer door seals
  4. Measuring the kingpin diameter

Explanation

The air brake portion of the inspection confirms the glad hands are sealed, the lines are not chafed, and the trailer brakes apply and release with tractor pressure. This ensures the trailer brakes will function and the combination will stop safely.

Question 7Combination Vehicle Inspection and Coupling/Uncoupling

When should you chock the trailer wheels during uncoupling?

  1. Only after the tractor has been driven away
  2. Only when the trailer is loaded
  3. Never, because the trailer spring brakes hold it
  4. Whenever the trailer could roll, such as on a slope or uncertain grade Correct answer.

Explanation

Chocking the trailer wheels prevents rolling whenever the trailer might move, especially on a grade or when you are unsure the spring brakes will hold. Once the tractor is removed, the trailer has no other restraint.

Question 8Combination Vehicle Inspection and Coupling/Uncoupling

What does the trailer air supply (emergency) line do when it is disconnected from the tractor?

  1. It supplies air to the trailer brakes to release them
  2. It vents air only to the trailer tires
  3. It has no effect because the trailer has its own compressor
  4. It loses pressure and causes the trailer spring brakes to apply Correct answer.

Explanation

The emergency line carries tractor air that holds the trailer spring brakes released. If it is disconnected, pressure drops and the trailer spring brakes automatically apply, which is the fail-safe design.

Question 9Combination Vehicle Inspection and Coupling/Uncoupling

After coupling and raising the landing gear, you must check the trailer air lines. What should you look for?

  1. Lines disconnected to prevent chafing
  2. Lines draped over the exhaust stack
  3. Lines coiled tightly around the kingpin
  4. Lines routed so they will not rub or catch on the tractor frame or fifth wheel Correct answer.

Explanation

Air lines must be supported and routed so they do not chafe against the frame, fifth wheel, or other parts as the combination turns. Chafed lines leak air and can cause brake loss or an emergency brake application.

Question 10Combination Vehicle Inspection and Coupling/Uncoupling

During the tug test, the trailer brakes are set and you pull gently forward. The tractor moves forward slightly but the trailer does not. What does this indicate?

  1. The fifth wheel jaws are locked around the kingpin Correct answer.
  2. The air lines are crossed
  3. The trailer brakes have failed
  4. The kingpin is not engaged and the trailer is being pushed

Explanation

If the jaws are properly locked, the trailer will resist the pull because its brakes are set and the kingpin is captured. The tractor may rock slightly, but the trailer should not move with it.

Question 11Combination Vehicle Inspection and Coupling/Uncoupling

What is the correct order for releasing the tractor parking brake and trailer spring brakes after a successful coupling?

  1. Release the tractor parking brake first, then the trailer air supply valve
  2. Open the glad hands, then release the tractor brake
  3. Push in the trailer air supply valve, then release the tractor parking brake Correct answer.
  4. Release both at the same time while in gear

Explanation

You first push in the trailer air supply valve to charge and release the trailer spring brakes, then release the tractor parking brake. This sequence ensures the trailer brakes are released and the system is charged before the vehicle moves.

Question 12Combination Vehicle Inspection and Coupling/Uncoupling

You notice the fifth wheel plate has a deep crack near the mounting area. What is the correct action?

  1. Couple anyway and monitor it during the trip
  2. Report it and place the vehicle out of service until repaired Correct answer.
  3. Weld it yourself before coupling
  4. Ignore it if the trailer is empty

Explanation

A cracked fifth wheel plate is a structural defect that can fail under load, so the vehicle must be repaired before use. You should report it and keep the combination out of service.

Question 13Combination Vehicle Inspection and Coupling/Uncoupling

When uncoupling, why should you pull the tractor slightly forward after releasing the fifth wheel jaws?

  1. To test the trailer brakes
  2. To stretch the air lines
  3. To reset the kingpin
  4. To let the trailer settle onto the landing gear before you drive away Correct answer.

Explanation

After the jaws release, pulling forward slowly lets the trailer nose settle onto the landing gear and confirms the trailer is stable. Then you can safely disconnect the air lines and drive clear.

Question 14Combination Vehicle Inspection and Coupling/Uncoupling

What is the function of the glad hands on a combination vehicle?

  1. They lock the kingpin into the fifth wheel
  2. They connect the trailer air lines to the tractor air system Correct answer.
  3. They hold the trailer landing gear in place
  4. They secure the mud flaps

Explanation

Glad hands are the couplers that join the tractor and trailer air lines, allowing brake and supply air to pass between them. They must be clean, sealed, and locked to prevent leaks.

Question 15Combination Vehicle Inspection and Coupling/Uncoupling

While inspecting the coupling, you see the fifth wheel jaws are closed but the release handle is not latched. What should you do?

  1. Pull the tractor forward to test the coupling without the latch
  2. Proceed, since the jaws are already closed
  3. Open the jaws and start over with a new trailer
  4. Latch the safety catch and re-verify the jaws are locked Correct answer.

Explanation

The release handle must be secured by its safety latch so vibration cannot open the jaws. Latch it and confirm the jaws remain locked around the kingpin before moving.

Question 16Combination Vehicle Inspection and Coupling/Uncoupling

How can you tell whether a trailer is equipped with spring brakes that will apply automatically when air is lost?

  1. Look for a hand valve on the trailer
  2. Check for the red supply valve and test that the trailer brakes apply when the line is disconnected Correct answer.
  3. Inspect the tire sidewalls for load rating
  4. Check whether the trailer has a parking brake lever

Explanation

Spring brakes are tested by disconnecting the emergency line or using the red trailer air supply valve; the brakes should apply when pressure is lost. This confirms the fail-safe system works.

Question 17Combination Vehicle Inspection and Coupling/Uncoupling

What should you check on the trailer landing gear during the pre-trip inspection?

  1. That the legs are retracted, the crank is secure, and there are no cracks or bends Correct answer.
  2. That the legs are fully extended and locked
  3. That the legs are greased with the crank removed
  4. That the legs touch the ground while driving

Explanation

Before driving, the landing gear must be fully retracted with the crank secured so it does not drag or strike the road. You also inspect the legs and crossmembers for cracks, bends, and missing parts.

Question 18Combination Vehicle Inspection and Coupling/Uncoupling

You are coupling on a slope and the trailer begins to roll as you back under it. What is the safest immediate response?

  1. Speed up to complete the coupling quickly
  2. Continue and rely on the fifth wheel to stop the roll
  3. Stop, set the trailer brakes or chock the wheels, and restart the procedure Correct answer.
  4. Signal a spotter to push the trailer back

Explanation

If the trailer moves during coupling, stop immediately and secure it with brakes or chocks before continuing. Trying to finish the coupling while the trailer rolls risks injury and damage.

Question 19Combination Vehicle Inspection and Coupling/Uncoupling

What is the correct procedure for disconnecting the air lines when uncoupling?

  1. Disconnect the service line first, then the emergency line
  2. Disconnect both at once by pulling the glad hands apart
  3. Disconnect the emergency line first, then the service line Correct answer.
  4. Leave the lines connected and drive away slowly

Explanation

The emergency (supply) line is disconnected first so the trailer spring brakes apply and hold the trailer. Then the service line can be disconnected safely.

Question 20Combination Vehicle Inspection and Coupling/Uncoupling

During a pre-trip inspection, you find the trailer's ABS lamp stays on after the ignition check. What does this mean?

  1. There is an ABS fault that should be repaired before the trip Correct answer.
  2. The lamp is only a bulb test and can be ignored
  3. The trailer is not equipped with ABS
  4. The ABS is functioning normally and the lamp will go out when moving

Explanation

An ABS lamp that remains on after the bulb check indicates a fault in the trailer ABS system. The vehicle should be repaired before use, since ABS performance may be reduced.

Question 21Combination Vehicle Inspection and Coupling/Uncoupling

When backing under a trailer, why should you use the lowest reverse gear and keep the tractor aligned with the trailer?

  1. To reduce impact forces and avoid damaging the kingpin and fifth wheel Correct answer.
  2. To warm up the transmission
  3. To keep the trailer brakes released
  4. To save fuel during coupling

Explanation

Backing slowly and straight reduces the impact when the fifth wheel contacts the kingpin plate, preventing damage to both. Misalignment can bend the kingpin or damage the plate.

Question 22Combination Vehicle Inspection and Coupling/Uncoupling

You are inspecting a combination vehicle and the trailer's spring brake chambers are cracked. What is the correct interpretation?

  1. The cracked chamber can leak air and must be repaired before use Correct answer.
  2. This is cosmetic and does not affect braking
  3. The crack improves ventilation and is acceptable
  4. Only the tractor brake chambers matter

Explanation

A cracked spring brake chamber can leak air and fail to apply or release the brakes properly, so it must be repaired before the vehicle is used. Brake chamber integrity is critical to stopping performance.

Question 23Combination Vehicle Inspection and Coupling/Uncoupling

When coupling, what is the correct sequence for connecting the air lines after the fifth wheel is locked?

  1. Connect the emergency (red) line first, then the service (blue) line
  2. Connect either line first; order does not matter
  3. Connect the lines before locking the fifth wheel
  4. Connect the service (blue) line first, then the emergency (red) line Correct answer.

Explanation

The service (blue) line is connected first, then the emergency (red) line, which charges the trailer system and releases the spring brakes. This order lets you confirm the trailer is properly supplied.

Question 24Combination Vehicle Inspection and Coupling/Uncoupling

A driver couples to a trailer, completes the tug test, and drives off, but the trailer separates at the first turn. Which inspection failure most likely caused this?

  1. The landing gear was left slightly extended
  2. The trailer ABS lamp was on
  3. The fifth wheel jaws were not locked around the kingpin and the release handle was unlatched Correct answer.
  4. The mud flaps were too long

Explanation

A separation on a turn usually means the kingpin was never captured by the jaws, often because the handle was unlatched or the jaws were not verified. The tug test can pass falsely if the trailer brakes hold the trailer even without a locked kingpin.

Question 25Combination Vehicle Inspection and Coupling/Uncoupling

During uncoupling on a slight grade, you set the trailer spring brakes but the trailer creeps backward. What is the best course of action?

  1. Continue uncoupling and rely on the tractor to hold it
  2. Chock the wheels and re-evaluate before releasing the fifth wheel Correct answer.
  3. Pull the tractor forward to stop the creep
  4. Release the spring brakes to let it roll to level ground

Explanation

If the trailer moves with spring brakes set, chock the wheels before releasing the fifth wheel so it cannot roll free. Then inspect the brake system and choose a safer location if needed.

Question 26Combination Vehicle Inspection and Coupling/Uncoupling

What is the primary purpose of the fifth wheel in a combination vehicle?

  1. To provide a pivot point that supports the front of the trailer and locks it to the tractor Correct answer.
  2. To supply air pressure to the trailer's brake system
  3. To keep the trailer's landing gear retracted during travel
  4. To connect the trailer's electrical system to the tractor

Explanation

The fifth wheel is a horseshoe-shaped coupling device mounted on the tractor frame. It supports the front weight of the trailer and allows the combination to pivot during turns while locking the trailer kingpin securely.

Question 27Combination Vehicle Inspection and Coupling/Uncoupling

When inspecting the kingpin area of a trailer during the pre-trip inspection, which condition requires the vehicle to be placed out of service?

  1. A cracked or bent kingpin Correct answer.
  2. A light coating of grease on the kingpin
  3. A missing or loose kingpin lock plate
  4. A small amount of rust on the fifth wheel plate

Explanation

A cracked or bent kingpin cannot safely hold the trailer to the fifth wheel and may fail during operation. Any structural damage to the kingpin is a critical defect that requires the vehicle to be taken out of service.

Question 28Combination Vehicle Inspection and Coupling/Uncoupling

During the pre-trip inspection, you check the trailer's spring brake chambers and notice a crack in the housing. What is the correct action?

  1. Reduce the trailer load to lessen brake strain
  2. Note it and continue the trip, monitoring for air loss
  3. Report it and have the chamber replaced before driving Correct answer.
  4. Apply a sealant to the crack and proceed

Explanation

A cracked spring brake chamber can fail suddenly and cause a loss of braking or a dragging brake. It must be replaced before the vehicle is operated; sealants or load reduction do not restore structural integrity.

Question 29Combination Vehicle Inspection and Coupling/Uncoupling

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

  1. To support the trailer so it does not fall when the tractor is pulled away Correct answer.
  2. To engage the trailer's spring brakes automatically
  3. To align the kingpin for the next coupling
  4. To take the weight off the tractor's rear suspension

Explanation

Lowering the landing gear transfers the trailer's weight to the ground, preventing the trailer from dropping and damaging the landing gear or kingpin when the tractor is removed. The gear must be firmly on the ground before the fifth wheel is released.

Question 30Combination Vehicle Inspection and Coupling/Uncoupling

What is the correct order of steps when coupling a tractor to a trailer?

  1. Raise landing gear, back under trailer, inspect fifth wheel, connect air lines, test coupling
  2. Back under trailer, inspect fifth wheel, raise landing gear, connect air lines, test coupling
  3. Connect air lines, back under trailer, test coupling, inspect fifth wheel, raise landing gear
  4. Inspect fifth wheel, back under trailer, connect air lines, test coupling, raise landing gear Correct answer.

Explanation

The coupling sequence begins with inspecting the fifth wheel and kingpin, then backing under the trailer until the jaws lock. After connecting the air lines and testing the coupling with a tug test, the landing gear is raised.

Question 31Combination Vehicle Inspection and Coupling/Uncoupling

During the tug test after coupling, the trailer brakes are locked and you pull gently forward. The tractor moves but the trailer does not. What does this indicate?

  1. The air lines are crossed
  2. The trailer brakes are not working
  3. The trailer spring brakes are released
  4. The fifth wheel jaws are not locked around the kingpin Correct answer.

Explanation

If the trailer moves with the tractor during a tug test with trailer brakes locked, the kingpin is not secured by the fifth wheel jaws. The coupling has failed and must be corrected before proceeding.

Question 32Combination Vehicle Inspection and Coupling/Uncoupling

What is the purpose of the trailer air supply (emergency) line in a combination vehicle?

  1. To operate the trailer's electrical lights
  2. To provide air to the trailer's suspension system
  3. To release the trailer's spring brakes when connected and apply them if the line is disconnected Correct answer.
  4. To supply air to the trailer's brake system for normal braking

Explanation

The emergency line supplies air to the trailer's spring brake chambers. When the line is disconnected or loses pressure, the spring brakes apply automatically, stopping the trailer.

Question 33Combination Vehicle Inspection and Coupling/Uncoupling

When uncoupling, why should you place the trailer's spring brakes in the applied position before releasing the fifth wheel?

  1. To make it easier to release the fifth wheel handle
  2. To keep the landing gear from sinking into soft ground
  3. To keep the trailer from rolling when the tractor is removed Correct answer.
  4. To prevent air loss from the trailer system

Explanation

With the trailer spring brakes applied, the trailer is held stationary after the tractor is pulled away. This prevents the trailer from rolling and potentially causing injury or damage.

Question 34Combination Vehicle Inspection and Coupling/Uncoupling

After coupling and connecting the air lines, you notice that the trailer air pressure gauge does not register any pressure. What is the most likely cause?

  1. The tractor's air compressor is overworking
  2. The glad hand seals are missing or damaged Correct answer.
  3. The trailer's ABS system is functioning normally
  4. The trailer spring brakes are released

Explanation

Missing or damaged glad hand seals prevent a tight connection, causing air to escape and preventing pressure buildup in the trailer. The seals should be inspected and replaced if defective.

Question 35Combination Vehicle Inspection and Coupling/Uncoupling

During the pre-trip inspection, you check the trailer's air lines and find a small cut in the service line. What should you do?

  1. Replace the line before operating the vehicle Correct answer.
  2. Ignore it if the cut is less than an inch long
  3. Connect the lines and check for leaks; if none, proceed
  4. Wrap it with tape and continue

Explanation

A cut in an air line can worsen and cause a sudden loss of braking pressure. Any damaged air line must be replaced; tape or size-based judgment is not acceptable.

Question 36Combination Vehicle Inspection and Coupling/Uncoupling

What is the correct procedure for testing the trailer's spring brakes after coupling?

  1. Release the tractor parking brake and pull forward
  2. Disconnect the emergency line and check for brake application
  3. Set the trailer brakes, release the tractor brakes, and try to pull forward Correct answer.
  4. Push the trailer brake valve in and listen for air loss

Explanation

To test trailer spring brakes, set the trailer brakes, release the tractor parking brake, and attempt to pull forward. The trailer brakes should hold and prevent movement.

Question 37Combination Vehicle Inspection and Coupling/Uncoupling

When inspecting the fifth wheel, which of the following indicates a potential problem that should be reported?

  1. A light film of grease on the plate
  2. A slightly worn kingpin
  3. A small amount of play in the fifth wheel
  4. A missing or broken release handle spring Correct answer.

Explanation

A missing or broken release handle spring can prevent the fifth wheel jaws from locking securely. This is a safety defect that must be repaired before coupling.

Question 38Combination Vehicle Inspection and Coupling/Uncoupling

During uncoupling, you have lowered the landing gear and released the fifth wheel jaws. What is the next step?

  1. Pull the tractor slowly forward until the kingpin is clear Correct answer.
  2. Lower the landing gear further to lift the trailer
  3. Disconnect the air lines and electrical cord
  4. Set the trailer spring brakes

Explanation

After releasing the fifth wheel jaws, pull the tractor slowly forward to clear the kingpin from the fifth wheel. This allows the trailer to remain stationary while the tractor is removed.

Question 39Combination Vehicle Inspection and Coupling/Uncoupling

What is the purpose of the trailer's landing gear?

  1. To support the trailer when it is not connected to a tractor Correct answer.
  2. To assist the suspension system
  3. To provide stability during turns
  4. To raise and lower the trailer for loading

Explanation

Landing gear is designed to support the front of the trailer when it is uncoupled from the tractor. It must be strong enough to hold the trailer's weight when parked.

Question 40Combination Vehicle Inspection and Coupling/Uncoupling

During a pre-trip inspection, you find that the trailer's ABS lamp stays on after the ignition check. What does this indicate?

  1. The trailer brakes are automatically applied
  2. The ABS system is functioning correctly
  3. The trailer's ABS system has a fault and may not work Correct answer.
  4. The electrical connection is good

Explanation

If the ABS lamp remains illuminated after the ignition check, it indicates a fault in the ABS system. The vehicle may still have normal braking but without ABS function, and the fault should be repaired.

Question 41Combination Vehicle Inspection and Coupling/Uncoupling

When backing under a trailer to couple, why should you use the lowest reverse gear and keep the tractor aligned with the trailer?

  1. To keep the trailer brakes released
  2. To prevent the trailer from rolling forward
  3. To save fuel during the coupling process
  4. To reduce the chance of hitting the trailer too hard and damaging the kingpin Correct answer.

Explanation

Using the lowest reverse gear gives you maximum control and reduces speed, minimizing the risk of a hard impact that could damage the kingpin or fifth wheel. Proper alignment ensures the kingpin enters the fifth wheel correctly.

Question 42Combination Vehicle Inspection and Coupling/Uncoupling

What is the correct way to check that the fifth wheel jaws have locked around the kingpin after coupling?

  1. Check that the trailer air pressure is above 100 psi
  2. Pull forward gently with the trailer brakes set
  3. Visually inspect that the jaws are closed and the release handle is latched Correct answer.
  4. Listen for a click when backing under

Explanation

A visual inspection confirms that the jaws are closed around the kingpin and the release handle is in the latched position. This is the most direct way to verify a secure coupling.

Question 43Combination Vehicle Inspection and Coupling/Uncoupling

You are coupling to a trailer and notice that the trailer's kingpin is slightly higher than the fifth wheel plate. What is the correct action?

  1. Adjust the trailer landing gear to raise or lower the trailer so the kingpin is at the correct height Correct answer.
  2. Back under slowly; the fifth wheel will lift the trailer
  3. Use a block to raise the tractor's fifth wheel
  4. Proceed; the fifth wheel will automatically adjust

Explanation

The kingpin must be at the correct height to enter the fifth wheel properly. Adjusting the landing gear ensures proper alignment and prevents damage to the coupling components.

Question 44Combination Vehicle Inspection and Coupling/Uncoupling

What is the purpose of the safety latch on the fifth wheel release handle?

  1. To lock the trailer brakes
  2. To indicate when the trailer is properly coupled
  3. To hold the air lines in place
  4. To prevent the release handle from accidentally opening Correct answer.

Explanation

The safety latch secures the release handle in the closed position, preventing accidental release of the fifth wheel jaws while driving. It must be engaged after coupling.

Question 45Combination Vehicle Inspection and Coupling/Uncoupling

During uncoupling, you have pulled the tractor forward and the trailer is standing on its landing gear. What should you do next?

  1. Disconnect the air lines and electrical cord from the tractor Correct answer.
  2. Lower the landing gear further
  3. Release the trailer spring brakes
  4. Back the tractor under the trailer again

Explanation

After the tractor is clear of the trailer, disconnect the air lines and electrical cord. This prevents damage to the lines and allows the tractor to be driven away.

Question 46Combination Vehicle Inspection and Coupling/Uncoupling

You are inspecting a combination vehicle and notice that the trailer's spring brake chambers are cracked. What is the correct interpretation?

  1. The cracks will not affect braking performance
  2. The cracks are normal wear and can be ignored
  3. The chambers can be repaired with epoxy
  4. The chambers are defective and must be replaced before driving Correct answer.

Explanation

Cracked spring brake chambers are a critical safety defect that can lead to brake failure. They must be replaced; repairs or ignoring the cracks are not acceptable.

Question 47Combination Vehicle Inspection and Coupling/Uncoupling

A driver couples to a trailer, completes the tug test, and drives off, but the trailer separates at the first turn. Which coupling step was most likely missed?

  1. Connecting the electrical cord
  2. Setting the trailer spring brakes
  3. Lowering the landing gear
  4. Checking that the fifth wheel jaws completely closed around the kingpin Correct answer.

Explanation

If the fifth wheel jaws do not fully close and lock around the kingpin, the trailer can separate under load. A visual inspection of the jaws and release handle is essential after coupling.

Question 48Combination Vehicle Inspection and Coupling/Uncoupling

During uncoupling on a slight grade, you set the trailer spring brakes but the trailer creeps backward. What is the best immediate action?

  1. Pull the tractor forward quickly
  2. Release the spring brakes and try again
  3. Place chocks under the trailer wheels Correct answer.
  4. Lower the landing gear further

Explanation

If the trailer moves despite spring brakes being set, chock the wheels to prevent rolling. This is the safest immediate action to control the trailer on a grade.

Question 49Combination Vehicle Inspection and Coupling/Uncoupling

What is the primary reason for inspecting the fifth wheel mounting bolts during the pre-trip inspection?

  1. To verify the trailer is properly lubricated
  2. To ensure they are tight and not missing, which could cause the fifth wheel to separate from the tractor Correct answer.
  3. To adjust the fifth wheel height
  4. To check for rust

Explanation

Loose or missing mounting bolts can allow the fifth wheel to detach from the tractor frame, causing a catastrophic failure. Inspecting and tightening them is a critical safety check.

Question 50Combination Vehicle Inspection and Coupling/Uncoupling

When inspecting the trailer's air lines, you notice that the service line and emergency line are crossed. What is the consequence?

  1. The landing gear will not operate
  2. The ABS system will be disabled
  3. The trailer brakes will not release properly and may drag Correct answer.
  4. The trailer lights will not work

Explanation

Crossed air lines can cause the trailer spring brakes to remain applied or release improperly, leading to dragging brakes or loss of braking control. The lines must be connected correctly.