CDL Combination Vehicles Sample Questions

Questions from each area of the CDL Combination Vehicles test. Pick an answer to see whether you're right, how everyone else did, and why.

CDL Combination Vehicles Test exam guide

1 Coupling and uncoupling—The procedures for proper coupling and uncoupling a tractor to a semi-trailer

During coupling, you fill the trailer's brake system with air by:

  1. pulling the trailer hand valve down.
  2. pushing the red air supply knob in.
  3. pulling the red air supply knob out.

Answer: B, pushing the red air supply knob in.. Pushing the red knob in opens the tractor protection valve, so air flows to the trailer and fills its tanks. Then wait for the pressure to reach normal. (CDL manual 6.2.3, 6.4.1)

After backing under the trailer, how should you test that the coupling holds?

  1. Raise the landing gear slightly, then pull forward gently with the trailer brakes released.
  2. Raise the landing gear slightly, then pull forward gently with the trailer brakes locked.
  3. Leave the landing gear down, then pull forward gently with the trailer brakes released.

Answer: B, Raise the landing gear slightly, then pull forward gently with the trailer brakes locked.. Lift the landing gear just off the ground. Then pull gently against the locked trailer brakes. If the kingpin is not held, the tractor pulls away from the trailer. (CDL manual 6.4.1)

2 Vehicle inspection—The objectives and proper procedures that are unique for performing vehicle safety inspections on combination vehicles

During a walk-around inspection, the lower fifth wheel of a tractor should be:

  1. free to slide, with no grease on it.
  2. firmly mounted, with no grease on it.
  3. firmly mounted, with enough grease on it.

Answer: C, firmly mounted, with enough grease on it.. The lower fifth wheel must be held tight to the frame, with no missing or damaged parts. It also needs enough grease to keep friction low between tractor and trailer. (CDL manual 6.5.1)

When you check the air lines between the tractor and trailer, they should be:

  1. pulled tight, with no slack that could sag.
  2. left loose, with no ties holding them up.
  3. secured, with just enough slack for turns.

Answer: C, secured, with just enough slack for turns.. The air lines must be held up so they cannot drag or get caught. They also need enough slack to bend when the rig turns, or they could pull apart. (CDL manual 6.5.1)

3 General operating practices and procedures

Why do you steer the front of a tractor-trailer wide around a corner?

  1. So drivers behind you can see your turn signal
  2. So the trailer stays lined up behind the tractor
  3. So the rear wheels do not ride over the curb

Answer: C, So the rear wheels do not ride over the curb. In a turn, the rear wheels cut inside the path of the front wheels. Taking the front out wide keeps the rear wheels off the curb and away from people standing there. (CDL manual 6.1.6)

On a newer air-brake trailer, the parking and emergency brakes are:

  1. hydraulic brakes.
  2. spring brakes.
  3. electric brakes.

Answer: B, spring brakes.. Newer trailers use spring brakes for parking and emergencies, the same as trucks and tractors. Only converter dollies and trailers built before 1975 may lack them. (CDL manual 6.2.8)