Free CDL Combination Vehicles Practice Test 2019

QUESTION NO: 1

When uncoupling, you should lower the landing gear before you __________

A. disconnect the air lines and electrical cable.
B. chock the trailer wheels.
C. position the rig.
D. none of the above

Answer: A

Explanation:

Knowing how to couple and uncouple correctly is basic to safe operation of combination vehicles. Coupling and uncoupling incorrectly can be very dangerous. General coupling and uncoupling steps can be helpful, but there are differences between different rigs. Learn the details of coupling and uncoupling the truck(s) you will operate. To uncouple safely, step one is to position the rig. Make sure the surface of the parking area can support the weight of the trailer. Have the tractor lined up with the trailer. (Pulling out at an angle can damage the landing gear.)
Step two is to ease the pressure on the locking jaws. Shut off the trailer air supply to lock the trailer brakes. Ease pressure on the fifth wheel locking jaws by backing up gently. (This will help you release the fifth wheel locking lever.) Put the parking brakes on while the tractor is pushing against the kingpin. (This will hold the rig with the pressure off the locking jaws.)
Step three is to chock the trailer wheels if the trailer doesn’t have spring brakes or if you’re not sure. (If the trailer doesn’t have spring brakes, the air could leak out of the trailer air tank, releasing its emergency brakes. Without chocks, the trailer could move.) The fourth step is to lower the landing gear.
If the trailer is empty, lower the landing gear until it makes firm contact with the ground. If the trailer is loaded, after the landing gear makes firm contact with the ground, turn the crank in a low gear a few extra turns. This will lift some weight off the tractor. (Do not lift the trailer off the fifth wheel.) This will make it easier to unlatch the fifth wheel and it will make it easier to couple the next time. Step five is to disconnect the air lines and electrical cable.
Disconnect the air lines from the trailer and connect the air glad hands to dummy couplers at the back of the cab or couple them together. Hang the electrical cable with the plug down to prevent moisture from entering it. Make sure the lines are supported so they won’t be damaged while you are driving the tractor.

QUESTION NO: 2

If you must back with a trailer on a curved path, back __________

A. toward the driver’s side.
B. in a straight line.
C. toward the passenger’s side.
D. any of the above

Answer: A

Explanation:

When backing a car, straight truck, or bus, you turn the top of the steering wheel in the direction you want to go. When backing a trailer, you turn the steering wheel in the opposite direction. Once the trailer starts to turn, you must turn the wheel the other way to follow the trailer. Whenever you back up with a trailer, try to position your vehicle so you can back in a straight line. If you must back on a curved path, back to the driver’s side so you can see. Look at your line of travel before you begin. Get out and walk around the vehicle.
Check your clearance to the sides and overhead, in and near the path your vehicle will take. Check the outside mirrors on both sides frequently. Get out of the vehicle and re-inspect your path if you are unsure. Back slowly. This will let you make corrections before you get too far off course. Correct drift immediately. As soon as you see the trailer getting off the proper path, correct it by turning the top of the steering wheel in the direction of the drift. When backing a trailer, make pull-ups to re-position your vehicle as needed.

QUESTION NO: 3

To secure the tractor during the uncoupling process, apply the __________ brake and place the transmission in __________

A. parking, reverse.
B. parking, neutral.
C. service, neutral.
D. service, reverse.

Answer: B

Explanation:

Knowing how to couple and uncouple correctly is basic to safe operation of combination vehicles. Coupling and uncoupling incorrectly can be very dangerous. General coupling and uncoupling steps can be helpful, but there are differences between different rigs. Learn the details of coupling and uncoupling the truck(s) you will operate. To uncouple safely, step eight is to secure the tractor by applying the parking brake and placing the transmission in neutral.

QUESTION NO: 4

In a trailer with no spring brakes, the __________ brakes will take over when the air stored in the trailer air tank is gone.

A. service
B. parking
C. emergency
D. none of the above

Answer: C

Explanation:

Newer trailers have spring brakes just like trucks and truck tractors. However, converter dollies and trailers built before 1975 are not required to have spring brakes. Those that do not have spring brakes have emergency brakes which work from the air stored in the trailer air tank. The emergency brakes come on whenever air pressure in the emergency line is lost.
These trailers have no parking brake. The emergency brakes come on whenever the air supply knob is pulled out or the trailer is disconnected. But the brakes will hold only as long as there is air pressure in the trailer air tank. Eventually, the air will leak away and then there will be no brakes. Therefore, it is very important for safety that you use wheel chocks when you park trailers without spring brakes. A major leak in the emergency line will cause the tractor protection valve to close and the trailer emergency brakes to come on.
You may not notice a major leak in the service line until you try to put the brakes on. Then, the air loss from the leak will lower the air tank pressure quickly. If it goes low enough, the trailer emergency brakes will come on.

QUESTION NO: 5

Step two of coupling is to __________

A. inspect the fifth wheel.
B. inspect the area and chock the wheels.
C. secure the tractor.
D. none of the above

Answer: B

Explanation:

Knowing how to couple and uncouple correctly is basic to safe operation of combination vehicles. Coupling and uncoupling incorrectly can be very dangerous. General coupling and uncoupling steps can be helpful, but there are differences between different rigs. Learn the details of coupling and uncoupling the truck(s) you will operate.
Step two is to inspect the area and chock the wheels. Make sure the area around the vehicle is clear. Be sure the trailer wheels are chocked or spring brakes are on. Make sure that any cargo is secured against movement due to the tractor being coupled to the trailer.

QUESTION NO: 6

When they are not in use, attach the glad hands to ___________ to prevent water and dirt from getting into the coupler and the air lines.

A. cut-out cocks
B. relay valves
C. dead-end couplers
D. none of the above

Answer: C

Explanation:

Glad hands are coupling devices used to connect the service and emergency air lines from the truck or tractor to the trailer. The couplers have a rubber seal which prevents air from escaping. Clean the couplers and rubber seals before a connection is made. When connecting the glad hands, press the two seals together with the couplers at a 90 degree angle to each other. A turn of the glad hand attached to the hose will join and lock the couplers.
Some vehicles have “dead end” or dummy couplers to which the hoses may be attached when they are not in use. This will prevent water and dirt from getting into the coupler and the air lines. Use the dummy couplers when the air lines are not connected to a trailer. If there are no dummy couplers, the glad hands can sometimes be locked together (depending on the couplings). It is very important to keep the air supply clean.

QUESTION NO: 7

In a converter dolly with no spring brakes, the emergency brakes will only hold so long as there is air pressure in the trailer __________

A. air tank.
B. air lines.
C. protection valve.
D. none of the above; the brakes will hold indefinitely.

Answer: A

Explanation:

Newer trailers have spring brakes just like trucks and truck tractors. However, converter dollies and trailers built before 1975 are not required to have spring brakes. Those that do not have spring brakes have emergency brakes which work from the air stored in the trailer air tank. The emergency brakes come on whenever air pressure in the emergency line is lost. These trailers have no parking brake. The emergency brakes come on whenever the air supply knob is pulled out or the trailer is disconnected.
But the brakes will hold only as long as there is air pressure in the trailer air tank. Eventually, the air will leak away and then there will be no brakes. Therefore, it is very important for safety that you use wheel chocks when you park trailers without spring brakes. A major leak in the emergency line will cause the tractor protection valve to close and the trailer emergency brakes to come on. You may not notice a major leak in the service line until you try to put the brakes on. Then, the air loss from the leak will lower the air tank pressure quickly. If it goes low enough, the trailer emergency brakes will come on.

QUESTION NO: 8

When uncoupling, you should inspect the trailer supports __________

A. after you pull the tractor clear of the trailer.
B. after you secure the tractor.
C. before you lower the landing gear.
D. none of the above

Answer: B

Explanation:

Knowing how to couple and uncouple correctly is basic to safe operation of combination vehicles. Coupling and uncoupling incorrectly can be very dangerous. General coupling and uncoupling steps can be helpful, but there are differences between different rigs. Learn the details of coupling and uncoupling the truck(s) you will operate. To uncouple safely, the fourth step is to lower the landing gear. If the trailer is empty, lower the landing gear until it makes firm contact with the ground.
If the trailer is loaded, after the landing gear makes firm contact with the ground, turn the crank in a low gear a few extra turns. This will lift some weight off the tractor. (Do not lift the trailer off the fifth wheel.) This will make it easier to unlatch the fifth wheel and it will make it easier to couple the next time. Step five is to disconnect the air lines and electrical cable. Disconnect the air lines from the trailer and connect the air glad hands to dummy couplers at the back of the cab or couple them together.
Hang the electrical cable with the plug down to prevent moisture from entering it. Make sure the lines are supported so they won’t be damaged while you are driving the tractor. In step six, unlock the fifth wheel. Raise the release handle lock. Pull the release handle to the “open” position. Keep your legs and feet clear of the rear tractor wheels to avoid serious injury in case the vehicle moves. Step seven is to pull the tractor partially clear of the trailer. Pull the tractor forward until the fifth wheel comes out from under the trailer.
Stop with the landing gear under the trailer (this prevents the trailer from falling to the ground if the landing gear should collapse or sink). In step eight, secure the tractor by applying the parking brake and placing the transmission in neutral. Step nine is to inspect the trailer supports. Make sure the ground is supporting the trailer and that the landing gear is not damaged. In step ten, pull the tractor clear of the trailer. Release the parking brakes. Check the area, then drive the tractor forward until it clears.

QUESTION NO: 9

Your following distance should be at least __________ for each ten feet of your vehicle length if you are going under 40 mph.

A. one second
B. two seconds
C. three seconds
D. four seconds

Answer: A

Explanation:

Trucks with trailers have a dangerous “crack-the-whip” effect. When you make a quick lane change, the crack-the-whip effect can turn the trailer over. There are many accidents where only the trailer overturns. “Rearward amplification” causes the crack-the-whip effect. Steer gently and smoothly when you are pulling trailers. If you make a sudden movement with your steering wheel, your trailer could tip over. Follow far enough behind other vehicles (at least one second for each ten feet of your vehicle length, plus another second if going over 40 mph).
Look far enough down the road to avoid being surprised and having to make a sudden lane change. At night, drive slowly enough to see obstacles with your headlights before it is too late to change lanes or stop gently. Slow down to a safe speed before going into a turn.

QUESTION NO: 10

You should connect the air lines to the trailer during step __________ of the coupling process.

A. six
B. seven
C. eight
D. nine

Answer: B

Explanation:

Knowing how to couple and uncouple correctly is basic to safe operation of combination vehicles. Coupling and uncoupling incorrectly can be very dangerous. General coupling and uncoupling steps can be helpful, but there are differences between different rigs. Learn the details of coupling and uncoupling the truck(s) you will operate.
In step seven, connect the air lines to the trailer. Check the glad hand seals and connect the tractor emergency air line to the trailer emergency glad hand. Check the glad hand seals and connect the tractor service air line to the trailer service glad hand. Make sure that the air lines are safely supported so they won’t be crushed or caught while the tractor is being backed under the trailer.

QUESTION NO: 11

Supply air to the service line during the pre-trip inspection with the __________

A. trailer air supply knob.
B. trailer hand brake.
C. emergency line shut-off valve.
D. none of the above

Answer: B

Explanation:

To check that air flows to all trailers during your pre-trip inspection, use the tractor parking brake and/or chock the wheels to hold the vehicle. Wait for the air pressure to reach normal, then push in the red “trailer air supply” knob. This will supply air to the emergency (supply) lines. Use the trailer handbrake to provide air to the service line. Go to the rear of the rig. Open the emergency line shut-off valve at the rear of the last trailer. You should hear air escaping, showing the entire system is charged. Close the emergency line valve.
Open the service line valve to check that service pressure goes through all the trailers (this test assumes that the trailer handbrake or the service brake pedal is on), and then close the valve. If you do NOT hear air escaping from both lines, check that the shut-off valves on the trailer(s) and dolly(ies) are in the OPEN position. You MUST have air all the way to the back for all the brakes to work.

QUESTION NO: 12

The __________ line is connected to relay valves, which allow the trailer brakes to be applied more quickly than would otherwise be possible.

A. control
B. emergency
C. supply
D. none of the above

Answer: A

Explanation:

Every combination vehicle has two air lines, the service line and the emergency line. They run between each vehicle (tractor to trailer, trailer to dolly, dolly to second trailer, etc.). 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. Depending on how hard you press the foot brake or hand valve, the pressure in the service line will similarly change. The service line is connected to relay valves. These valves allow the trailer brakes to be applied more quickly than would otherwise be possible.

QUESTION NO: 13

If you use the trailer hand valve for parking, __________

A. it might make the spring brakes fail.
B. wheel chocks will not be necessary.
C. air might leak out and unlock the brakes.
D. none of the above

Answer: C

Explanation:

Never use the trailer hand valve for parking because all the air might leak out, unlocking the brakes (in trailers that don’t have spring brakes). Always use the parking brakes when parking. If the trailer does not have spring brakes, use wheel chocks to keep the trailer from moving.

QUESTION NO: 14

To test the trailer emergency brakes, you will pull out the __________
A. tractor protection valve control.
B. trailer emergency valve.
C. trailer air supply control.
D. any of the above

Answer: D

Explanation:

During the pre-trip inspection of your combination vehicle, test the trailer emergency brakes. Charge the trailer air brake system and make sure the trailer rolls freely. Then stop and pull out the trailer air supply control (also called the tractor protection valve control or the trailer emergency valve) or place it in the “emergency” position. Pull gently on the trailer with the tractor to be sure the trailer emergency brakes are on.

QUESTION NO: 15

Answer: A

Converter dollies and trailers that do not have spring brakes have emergency brakes which work from the air stored in the trailer __________

A. air tank.
B. air lines.
C. protection valve.
D. none of the above

Explanation:

Newer trailers have spring brakes just like trucks and truck tractors. However, converter dollies and trailers built before 1975 are not required to have spring brakes. Those that do not have spring brakes have emergency brakes which work from the air stored in the trailer air tank. The emergency brakes come on whenever air pressure in the emergency line is lost. These trailers have no parking brake. The emergency brakes come on whenever the air supply knob is pulled out or the trailer is disconnected. But the brakes will hold only as long as there is air pressure in the trailer air tank. Eventually, the air will leak away and then there will be no brakes.
Therefore, it is very important for safety that you use wheel chocks when you park trailers without spring brakes. A major leak in the emergency line will cause the tractor protection valve to close and the trailer emergency brakes to come on.
You may not notice a major leak in the service line until you try to put the brakes on. Then, the air loss from the leak will lower the air tank pressure quickly. If it goes low enough, the trailer emergency brakes will come on.

QUESTION NO: 16

The tractor protection valve will __________ if air pressure is in the range of 20 to 45 psi.

A. unlock the spring brakes
B. cause the wheels to lock up
C. close automatically
D. none of the above

Answer: C

Explanation:

The tractor protection valve keeps air in the tractor or truck should the trailer break away or develop a bad leak. The tractor protection valve is controlled by the “trailer air supply” control valve in the cab. The control valve allows you to open and shut the tractor protection valve.
The tractor protection valve will close automatically if air pressure is low (in the range of 20 to 45 psi). When the tractor protection valve closes, it stops any air from going out of the tractor. It also lets the air out of the trailer emergency line. This causes the trailer emergency brakes to come on, with possible loss of control.

QUESTION NO: 17

Which of the following statements regarding hose couplers is false?

A. You should clean couplers and rubber seals before connecting the glad hands.
B. Turning the glad hand attached to the hose will join and lock the couplers.
C. Couplers have a steel seal which prevents air from escaping.
D. none of the above

Answer: C

Explanation:

Glad hands are coupling devices used to connect the service and emergency air lines from the truck or tractor to the trailer. The couplers have a rubber seal which prevents air from escaping. Clean the couplers and rubber seals before a connection is made. When connecting the glad hands, press the two seals together with the couplers at a 90 degree angle to each other.
A turn of the glad hand attached to the hose will join and lock the couplers. Some vehicles have “dead end” or dummy couplers to which the hoses may be attached when they are not in use. This will prevent water and dirt from getting into the coupler and the air lines. Use the dummy couplers when the air lines are not connected to a trailer. If there are no dummy couplers, the glad hands can sometimes be locked together (depending on the couplings). It is very important to keep the air supply clean.

QUESTION NO: 18

When you are driving a lightly-loaded combination vehicle, __________

A. you will be able to stop less quickly than if the vehicle were fully loaded.
B. the vehicle will have better traction.
C. the wheels will be less likely to lock up.
D. none of the above

Answer: A

Explanation:

Control your speed whether fully loaded or empty. Large combination vehicles take longer to stop when they are empty than when they are fully loaded. When lightly loaded, the very stiff suspension springs and strong brakes give poor traction and make it very easy to lock up the wheels. Your trailer can swing out and strike other vehicles.
Your tractor can jackknife very quickly. You also must be very careful about driving “bobtail” tractors (tractors without semitrailers). Tests have shown that bobtails can be very hard to stop smoothly. It takes them longer to stop than a tractor-semitrailer loaded to maximum gross weight. In any combination rig, allow lots of following distance and look far ahead, so you can brake early. Don’t be caught by surprise and have to make a “panic” stop.

QUESTION NO: 19

You should check the tractor-trailer connection for security during step __________ of the coupling process.

A. ten
B. eleven
C. twelve
D. none of the above

Answer: B

Explanation:

Knowing how to couple and uncouple correctly is basic to safe operation of combination vehicles. Coupling and uncoupling incorrectly can be very dangerous. General coupling and uncoupling steps can be helpful, but there are differences between different rigs. Learn the details of coupling and uncoupling the truck(s) you will operate.
Step eleven is to check the connection for security. Raise the trailer landing gear slightly off the ground. Pull the tractor gently forward while the trailer brakes are still locked to check that the trailer is locked onto the tractor.

QUESTION NO: 20

To lock the trailer brakes, __________

A. apply and release the trailer brakes, making sure the air pressure is up to normal.
B. push in the air supply knob or move the tractor protection valve from the emergency to the normal position.
C. pull out the air supply knob or move the tractor protection valve control from the normal to the emergency position.
D. none of the above

Answer: C

Explanation:

Knowing how to couple and uncouple correctly is basic to safe operation of combination vehicles. Coupling and uncoupling incorrectly can be very dangerous. General coupling and uncoupling steps can be helpful, but there are differences between different rigs. Learn the details of coupling and uncoupling the truck(s) you will operate. Step nine of the coupling process is to lock the trailer brakes. Pull out the “air supply” knob or move the tractor protection valve control from “normal” to “emergency.”

QUESTION NO: 21

To unlock the fifth wheel, __________

A. lower the release handle lock.
B. pull the release handle to the open position.
C. position your legs and feet underneath the rear tractor wheels.
D. none of the above

Answer: B

Explanation:

Knowing how to couple and uncouple correctly is basic to safe operation of combination vehicles. Coupling and uncoupling incorrectly can be very dangerous. General coupling and uncoupling steps can be helpful, but there are differences between different rigs. Learn the details of coupling and uncoupling the truck(s) you will operate.
To unlock the fifth wheel in step six of the uncoupling process, raise the release handle lock. Pull the release handle to the “open” position. Keep your legs and feet clear of the rear tractor wheels to avoid serious injury in case the vehicle moves.

QUESTION NO: 22

More than half of truck driver deaths in crashes are the result of __________

A. trailer jackknifes.
B. offtracking.
C. truck rollovers.
D. none of the above

Answer: C

Explanation:

More than half of truck driver deaths in crashes are the result of truck rollovers. When more cargo is piled up in a truck, the “center of gravity” moves higher up from the road. The truck becomes easier to turn over. Fully loaded rigs are ten times more likely to roll over in a crash than empty rigs. Rollovers happen when you turn too fast. Drive slowly around corners, on ramps, and off ramps. Avoid quick lane changes, especially when fully loaded.

QUESTION NO: 23

Dollies manufactured on or after March 1, 1998, are required to have a __________ ABS malfunction lamp on the left side.

A. red
B. white
C. yellow
D. any of the above

Answer: C

Explanation:

All trailers and converter dollies built on or after March 1, 1998, are required to have ABS. However, many trailers and converter dollies built before this date have been voluntarily equipped with ABS. Trailers will have yellow ABS malfunction lamps on the left side, either on the front or rear corner.
Dollies manufactured on or after March 1, 1998, are required to have a lamp on the left side. In the case of vehicles manufactured before the required date, it may be difficult to tell if the unit is equipped with ABS. Look under the vehicle for the ECU and wheel speed sensor wires coming from the back of the brakes.

QUESTION NO: 24

Water and oil in the trailer air tanks __________

A. helps the brakes work correctly.
B. should be drained and replaced every three months.
C. do not have to be checked if the vehicle has automatic drains.
D. none of the above

Answer: D

Explanation:

Each trailer and converter dolly has one or more air tanks. They are filled by the emergency (supply) line from the tractor. They provide the air pressure used to operate trailer brakes. Air pressure is sent from the air tanks to the brakes by relay valves. The pressure in the service line tells how much pressure the relay valves should send to the trailer brakes. The pressure in the service line is controlled by the brake pedal (and the trailer hand brake).
It is important that you don’t let water and oil build up in the air tanks. If you do, the brakes may not work correctly. Each tank has a drain valve on it and you should drain each tank every day. If your tanks have automatic drains, they will keep most moisture out. But you should still open the drains to make sure.

QUESTION NO: 25

If the __________ doesn’t work correctly, the emergency brakes could come on and cause you to lose control of your vehicle.

A. tractor protection valve
B. tractor parking brake
C. trailer air supply control
D. both A and C

Answer: D

Explanation:

During your pre-trip inspection on a combination vehicle, test the tractor protection valve. Charge the trailer air brake system (that is, build up normal air pressure and push the “air supply” knob in). Shut the engine off. Step on and off the brake pedal several times to reduce the air pressure in the tanks.
The trailer air supply control (also called the tractor protection valve control) should pop out (or go from “normal” to “emergency” position) when the air pressure falls into the pressure range specified by the manufacturer (usually within the range of 20 to 45 psi). If the tractor protection valve doesn’t work right, an air hose or trailer brake leak could drain all the air from the tractor. This would cause the emergency brakes to come on, with possible loss of control.