Combination 3

On a double or triple vehicle, which wheels off-track the most? 1. The rear wheels of the last trailer 2. The rear wheels of the first trailer 3. The rear wheels of the tractor

CORRECT ANSWER: 1. The rear wheels of the last trailer EXPLANATION: If there is more than one trailer, the rear wheels of the last trailer will off-track the most

Before you back under a trailer, make sure the: 1. Trailer brakes are locked 2 Tractor protection valve is normal 3. Air brakes are off

CORRECT ANSWER: 1. Trailer brakes are locked EXPLANATION: Pull out the air supply knob or move the tractor protection valve control from normal to emergency.

In general, the higher your truck's center of gravity, the 1. easier it is to turn over. 2. easier it is to turn around corners. 3. more stable it is when turning.

CORRECT ANSWER: 1. easier it is to turn over. EXPLANATION: The height of the vehicle's center of gravity is very important for safe handling. A high center of gravity means you are more likely to tip over.

When you test the tractor protection valve, the red air supply control knob should go into the ________ position. 1. emergency 2. normal 3. neutral

CORRECT ANSWER: 1. emergency EXPLANATION: -45 psi, the trailer air supply control knob should pop out, or the valve control should go from the "normal" to the "emergency" position.

Combination vehicles take longer to stop when they are empty than when they are fully loaded, because 1. there is less traction. 2. you're unlikely to brake as hard. 3. the center of gravity is lower.

CORRECT ANSWER: 1. there is less traction. EXPLANATION: 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.

Why should you lock the tractor glad hands to each other or to the storage bracket when you are not towing a trailer? 1. The connected brake circuit becomes a backup air tank 2. It will keep dirt and water out of the lines 3. If you did not, you could never build system pressure

CORRECT ANSWER: 2. It will keep dirt and water out of the lines EXPLANATION: If there are no dummy couplers, the glad hands can sometimes be locked together. It is very important to keep the air supply clean and free of moisture.

You are coupling a tractor to a semi-trailer and have backed up but are not under it. What should you hook up before backing under? 1. The electrical service cable 2. The emergency and service air lines 3. Nothing; back up and lock the fifth wheel

CORRECT ANSWER: 2. The emergency and service air lines EXPLANATION: Check glad hand seals and connect tractor emergency and service air-line to trailer emergency and service glad hand. Make sure air-lines are safely supported where they won't be crushed or caught while tractor is backing under the trailer.

You are driving a combination vehicle when the trailer breaks away, pulling apart both air lines. You would expect the trailer brakes to come on and: 1. The tractor to lose all air pressure 2 The tractor protection valve to close 3. The trailer supply valve to stay open 4. System parking brake will close

CORRECT ANSWER: 2. The tractor protection valve to close EXPLANATION: The tractor protection valve keeps air in the tractor or truck brake system 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.

The hand valve should be used: 1. Only with the foot brake 2. To test the trailer brakes 3. Only when the trailer is fully loaded

CORRECT ANSWER: 2. To test the trailer brakes EXPLANATION: The trailer hand valve, also called the trolley valve or Johnson bar, works the trailer brakes. The trailer hand valve should be used only to test the trailer brakes.

At night, when a vehicle is carrying a load that extends four feet or more beyond the rear of the body, there must be _______ at the extreme end of the load. 1. red flags 2. red lights 3. a red flag

CORRECT ANSWER: 2. red lights EXPLANATION: According to federal regulations, if the load projects more than 4 feet behind the rear of the vehicle, the end of the load must be marked as follows: (1) with red flags, each 18 inches square, in the daytime; or (2) with two red lights at night.

Almost half of all truck driver deaths are the result of 1. following too closely. 2. rollovers. 3. speed.

CORRECT ANSWER: 2. rollovers. EXPLANATION: More than half of truck driver deaths in crashes are the result of truck rollovers.

When coupling, the proper position of the fifth wheel is 1. level with the ground. 2. tilted down toward the rear of the tractor. 3. tilted up toward the rear of the tractor.

CORRECT ANSWER: 2. tilted down toward the rear of the tractor. EXPLANATION: Check if fifth wheel is in proper position for coupling: The fifth wheel should be tilted down toward rear of tractor.

To uncouple a loaded trailer, after the landing gear has made firm contact with the ground, you should 1. turn the crank a few more times until the trailer is lifted off the fifth wheel. 2. turn the crank a few more times to lift some weight off the tractor. 3. secure the crank handle safely.

CORRECT ANSWER: 2. turn the crank a few more times to lift some weight off the tractor. EXPLANATION: If trailer is loaded, after the landing gear makes firm contact with the ground, turn crank in low gear a few extra turns. This will lift some weight off the tractor making it easier to unlatch fifth wheel, and to recouple to the trailer.

The tractor protection valve is designed to close automatically when the air pressure falls into the pressure range specified by the manufacturer, typically 1. 75 to 100 psi. 2. 50 to 75 psi. 3. 20 to 45 psi.

CORRECT ANSWER: 3. 20 to 45 psi. EXPLANATION: 's specification usually 20 - 45 psi.

The air leakage rate for a combination vehicle (engine off, brakes on) should not be more than ____ PSI per minute. 1. 2 2. 3 3. 4

CORRECT ANSWER: 3. 4 EXPLANATION: With a fully-charged air system, turn off the engine, release the parking brake; and time the air pressure drop. The loss rate should be less than three psi in one minute for combination vehicles, adding one second if the brakes are applied.

Which of these vehicles off-tracks the most? 1. A 5-axle tractor towing a 45-foot trailer 2. A 5-axle tractor towing a 42-foot trailer 3. A 5-axle tractor towing a 52-foot trailer

CORRECT ANSWER: 3. A 5-axle tractor towing a 52-foot trailer EXPLANATION: When a vehicle goes around a corner the rear wheels follow a different path than the front wheels, and this is called off-tracking or "cheating." Longer vehicles will off-track more. If there is more than one trailer, the rear wheels of the last trailer will off-track the most.

The front trailer supports are up, and the trailer is resting on the tractor, make sure: 1. There is enough clearance between the tops of the tractor tires and the nose of the trailer 2. There is enough clearance between the tractor frame and the landing gear 3. Both answers are correct

CORRECT ANSWER: 3. Both answers are correct EXPLANATION: Check for enough clearance between rear of tractor frame and landing gear and between the top of the tractor tires and the nose of the trailer.

Which statement best illustrates the "crack-the-whip" effect? 1. The trailer is half full, and the cargo is loaded in the front of the trailer. When making a sudden movement of the steering wheel, the cargo will tend to forcefully slide to the back of the trailer, forcing the trailer to roll over. 2 When making a quick lane change or sudden movement of the steering wheel, the tractor tends to rock and sway. The velocity of the rearmost trailer forces the tractor to roll over before the trailer. 3. When making a quick lane change or sudden movement of the steering wheel, the rear trailer tends to swing out. The force of the rear trailer becomes amplified, causing it to roll over.

CORRECT ANSWER: 3. When making a quick lane change or sudden movement of the steering wheel, the rear trailer tends to swing out. The force of the rear trailer becomes amplified, causing it to roll over. EXPLANATION: Trucks with trailers have a dangerous crack-the-whip effect caused by rearward amplification. 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 has overturned.

If the brakes did not release when you pushed the trailer air supply valve, you should 1. check the electrical cables. 2. cross the air lines. 3. check the air line connections.

CORRECT ANSWER: 3. check the air line connections. EXPLANATION: If you do cross the air-lines, supply air will be sent to the service line instead of going to charge the trailer air tanks. Air will not be available to release the trailer spring brakes. If the spring brakes don't release when you push the trailer air supply control, check the air-line connections.

To test the tractor protection valve, charge the trailer air brake system, turn off the engine, and 1. keep pressing the brake pedal firmly. 2. . flash your high-beam headlights on and off several times. 3. step on and off the brake pedal several times.

CORRECT ANSWER: 3. step on and off the brake pedal several times. EXPLANATION: 's specification usually 20 - 45 psi. This will cause the spring brakes to come on.