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Flashcards in Combination Deck (49):

What two things are important to prevent rollovers?

•keep the cargo as close to the ground as possible

•drive slowly around turns


What is the emergency aid line for?

It supplies air to the trailer air tanks and controls the emergency brakes on combination vehicles.


What is offtracking?

Offtracking is when the rear wheels follow a different path than the front wheels.


Which shut-off valves should be open and which closed?

The front trailers shut-off valves open and the rear closed.


What might happen if the trailer is too high when you try to couple?

It may not couple correctly.


After coupling how much space should be between the upper and lower fifth wheel?

There should be no space!


Check for normal air pressure, release the parking brakes, move the vehicle forward slowly, and apply the trailer with the hand control trolley valve, if so equipped.

This is how you can test the trailer service brakes.


When you turn suddenly while pulling double trailers which trialled is most liked to turn over?

The rear trailer


TRUE or FALSE to drive you need to raise the landing gear only until it just lifts off the pavement.



What describes what the trailer air supply control does?

You push it in to supply the trailer with air, and pull it out to shut the air off and put on the trailer emergency brakes


Where are the shut-off valves?

At the back of each trailer.


Why should you not use the trailer hand valve while driving?

It should not be used while driving because of the danger of making the trailer skid


The service line carries air which is controlled by:

•the foot brake or trailer hand brake

•the foot brake

•the trailer hand break


Why should goi not use the trailer hand brake to straighten out a jackknifing trailer?

The trailer wheels caused the skid in the first place. Once the trailer wheels grip the road again, the trailer will start to follow the tractor and straighten out.


TRUE or FLASE should you look into the back of the fifth wheel to see if is is locked onto the kingpin?



Why should you use chocks when parking a trailer without spring brakes?

If the air supply in the trailer air tank had leaked away there will be no emergency brakes enabling the trailer wheels to turn freely


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, then close the valve. If you do NOT hear air escaping from both lines, check that the shut-off valves on the trailers and dollys are in the OPEN position.

This is how you test that air flows to all trailers.


Charge the trailer air brake system and check that the trailer rolls freely. Then stop and pull out the trailer air supply control valve. Pull gently on the trailer with the tractor to check that the trailer emergency brakes are on.

This is how you can test the trailer emergency brakes


Charge the trailer air brake system 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 should pop out when the air pressure falls into the pressure range specified by the manufacturer.

This is how you can test the tractor protection valve


You should not back a tractor under a trailer until the whole air system is:

At normal pressure


You are coupling a semi trailer to your tractor but have not yet backed under. The trailer is at the right height when:

It will be raised slightly when the tractor is backed under it


Which part of the kingpin should the locking jaws close around?

The shank


When you get ready to back under the semi trailer you should line up:

Directly in front of the trailer


How should you test the tractor semi trailer connection for security ?

Pull gently forward in low gear against the locked trailer brakes, then look at it carefully.


When should you use the hand valve to park a combination vehicle?



You supply air to the trailer tanks by:

Pushing in the trailer air supply valve


Why should you be sure that the fifth wheel plate is greased as required?

To prevent steering problems


After you supply air to the trailer, make sure the air lines are not crossed and the trailer brakes are working. This is done by:

Applying and releasing the trailer brakes and listening for brake sounds


There are two things that a driver can do to prevent a roll over. They are: (1) keep the cargo as close to the ground as possible; and (2):

Go slowly around turns


Before you back under a trailer, make sure the:

Trailer brakes are locked


If the service air line comes apart while you are driving a combination vehicle but the emergency lines stay together, what will happen right away?

Nothing is likely to happen until you try to apply the brakes


The air leakage rate for a combination vehicle (engine off, brakes on) should not be more than _____ psi per minute.



In normal driving some drivers use the hand valve before applying the brake pedal to prevent a jackknife. Which of these statements is true?

It should not be done


The driver crosses the air lines when hooking up to an old trailer. What will happen?

If the trailer has no spring brakes, you can drive away, but you will not have trailer brakes.


Why should you lock the tractor glad hands (or dummy couplers) to each other when you are not towing a trailer?

It will keep dirt and water out of the lines.


The safety catch for the fifth wheel locking lever must be ___ for a coupling to be complete.

Over the locking lever


The front trailer supports are up and the trailer is resting on the tractor. Make sure there is enough clearance between the:

•tractor frame and the landing gear

•the tops of the tractor tires and the nose of the trailer.


You have s major leak in the service line and you put on the brakes. Service air pressure will escape and cause the:

Trailer emergency brakes to come on


When backing under a tractor under a trailer you should expect:

Trailer will be lifted slightly when the tractor backs under it


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?

The emergency and service air lines


You have coupled with a semi trailer. In what position should you put the front trailer supports before driving away?

Fully raised with the crank handle secured in its bracket


Air lines on a combination vehicle are often colored to keep them from getting mixed up. The emergency line is ____; the service line is ___.

Red , blue


This is s true statement:

Bobtail tractors can take longer to stop than a combination vehicle loaded to the maximum gross weight.


You are coupling a tractor and semi trailer and have connected the air lines. Before backing under the trailer, you should:

Supply air to the trailer system, then pull out the air supply knob to lock the trailer brakes.


The hand valve should be used:

To test the trailer brakes


The air leakage rate for a combination vehicle should be no more than __ psi per minute



The fifth wheel locking lever is not locked after the jaws close around the kingpin. This means that:

The coupling is not right and should be fixed before driving the vehicle.


You are driving a combination vehicle when the trailer breaks away, pulling apart both air lines. You would expect the trailer breaks to come on and:

The tractor protection valve to close.


Semi trailers made before 1975 that are equipped with air brakes

Often do not have spring brakes