North Dakota CDL: Combination Vehicles Practice Test

Not quite. The answer is your brakes might fail.

On a combination vehicle, the brakes on the tractor and all trailers must work properly. If your combination vehicle is equipped with air brakes, check that air flows to all trailers and test both the trailer service brakes and the trailer emergency brakes.

Not quite. The answer is The trailer emergency brakes will come on.

The trailer air supply valve (which is manually controlled by the red dashboard knob) senses air pressure in the supply (emergency) line. If air pressure in the supply line is lost, the trailer air supply valve will close automatically, and the resulting loss of air pressure in the tractor protection valve will cause it to close as well. And loss of pressure in the supply line will cause the trailer emergency (spring) brakes to come on.

Not quite. The answer is supply air to the trailer system and then pull out the air supply knob.

Before backing under the trailer, check that the trailer brakes are working and then lock the trailer brakes. Once you've attached the air lines, there are a number of checks you should make: Check the glad hand seals. Make sure that the air lines won't be caught or crushed when you back under the trailer. Charge the trailer air brake system and verify that it's working without significant air loss. Then set the trailer air supply control to shut off the air and put on the trailer emergency brakes.

Not quite. The answer is the tractor protection valve control (trailer air supply control) will pop out or go from "normal" to "emergency."

When you test the tractor protection valve, the tractor protection valve control (also called the trailer air supply control) should pop out or go from the "normal" to the "emergency" position. This shows that the tractor protection valve has closed automatically to keep the air pressure from falling too far.

Not quite. The answer is carries air to a relay valve that allows the trailer brakes to be applied quickly.

The service line (also called the control line or signal line) carries air, which is controlled by the foot brake or the trailer hand brake. The service line is connected to relay valves that allow the trailer brakes to be applied more quickly. The relay valves send air to the brake chambers in response to the air pressure in the service line.

Not quite. The answer is Nothing is likely to happen until you try to apply the brakes.

If a leak has developed in the service line, air tank pressure may remain close to normal – until you try to brake. Then the air loss from the leak will cause the air pressure to drop quickly. If the air pressure drops far enough, the emergency brakes will come on.

Not quite. The answer is back up gently to ease pressure on the fifth wheel locking jaws.

When uncoupling, ease pressure on the fifth wheel locking jaws by backing up gently. (This will help you release the fifth wheel locking lever.) Then apply the parking brakes while the tractor is pushing against the kingpin.

Not quite. The answer is It will keep dirt and water out of the lines.

Some vehicles are equipped with "dead-end" or dummy couplers. When the air lines are not connected to a trailer, connect the glad hands to the dummy couplers to keep water and dirt out of the glad hands and air lines. If your vehicle doesn't have dummy couplers, you may be able to connect the glad hands to each other.

Not quite. The answer is secured but with enough slack for turns.

During your walk-around inspection, make sure that the electrical and air lines are secure but have enough slack to stay attached and secure even when the vehicle is turning.

Not quite. The answer is to test the trailer brakes.

The trailer hand valve (also known as a trolley valve or Johnson bar) controls only the trailer brakes, not the tractor brakes. You can use it to test the trailer brakes. Don't use it while you're driving, though. If you apply it while you're driving, you'll brake the trailers but not the tractor, which can cause a skid. Instead, use the foot brake, which sends air to the tractor brakes as well as the trailer brakes.

Not quite. The answer is directly in front of the trailer.

When you're ready to couple, position your tractor right in front of the trailer. If you were to back into the trailer at an angle, you might push it sideways and break the landing gear.

Not quite. The answer is turn the crank a few more times to lift some weight off the tractor.

After the landing gear has made firm contact with the ground, turn the crank in low gear a few more times to take some weight off the tractor, but not so much that you lift the trailer off the fifth wheel. This will make it easier to unlatch the fifth wheel and couple the trailer the next time.

Not quite. The answer is see it in your mirrors.

The earliest way to notice that your trailer is jackknifing is to see it swinging out in your mirrors.

Not quite. The answer is A tractor pulling three trailers

The last trailer of a triple is 3.5 times more likely to roll over than a five-axle tractor. This is known as the crack-the-whip effect. When pulling a triple, increase your following distance, avoid sudden moves, and steer gently. At night, don't drive faster than your headlight range.

Not quite. The answer is Yes, if you're not sure of your path of travel.

Backing a combination vehicle is potentially hazardous. Before you start to back up, check your intended path of travel. Exit the cab and walk around the vehicle. Check your clearance to the sides and overhead, in and near the path of your vehicle.

Not quite. The answer is To prevent steering problems

There shouldn't be any space between the upper and lower fifth wheel. However, friction could cause steering problems. To reduce friction, make sure that the fifth wheel plate is well lubricated as required.

Not quite. The answer is The shank

Don't drive the vehicle until you're sure that the coupling is correct. Check to make sure of the following: There is no space between the upper and lower fifth wheel, the fifth wheel jaws have closed around the shank of the kingpin, the locking lever is in the "lock" position, and the safety latch is in position over the locking lever. If anything isn't right, don't drive the vehicle until you've found and corrected the problem. If you drive it anyway, your trailer could come loose while you're driving.

Not quite. The answer is trailer emergency brakes to come on.

With the loss of air pressure, the tractor protection valve will close and the trailer emergency brakes will come on.

Not quite. The answer is When you lock the drive wheels on the tractor and the tractor spins out sideways as the trailer continues to push forward

A jackknife is usually the result of a drive-wheel skid. The tractor's rear drive wheels lock, and the trailer starts to push the tractor sideways.

Not quite. The answer is get away from your vehicle and call 911 or the posted emergency number.

A train traveling at 60 mph can take more than a mile to come to a complete stop. If your vehicle gets stuck on a railroad track, don't spend any time trying to free your vehicle. Get out of your vehicle and walk quickly at about a 45-degree angle to the tracks in the direction from which you expect trains to approach. That way, if your vehicle is hit, you won't be struck by flying debris. Call 911 or the telephone number on the railroad crossing sign for assistance.