CDL Combination Vehicle Practice Test

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Questions and Answers

A tractor with a(n) ________ trailer requires the shortest amount of stopping distance.

fully loaded

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

What could happen if you do not do the final air brake check for air leaks before driving?

you could lose your brakes while driving

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

the shank Signup and view all the answers

Glad hands are used to connect the....

service and emergency air lines from the truck or tractor to the trailer Signup and view all the answers

Trucks roll over more easily when fully loaded and are ...

ten times more likely to roll over in a crash than empty rigs Signup and view all the answers

In general, the higher your truck's center of gravity, the...

easier it is to turn over Signup and view all the answers

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...

the tractor protection valve to close Signup and view all the answers

When you drive a set of doubles, which shut-off valve must be closed in the last trailer?

Back section Signup and view all the answers

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 you drive the coupled unit Signup and view all the answers

What gear should the tractor engine be in after you uncouple the trailer and are inspecting the trailer?

neutral Signup and view all the answers

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 Signup and view all the answers

If the brakes did not release when you pushed the trailer air supply valve, you should...

check the air line connections Signup and view all the answers

You have a major leak in the service line, and you apply the brakes. Service air pressure will escape and cause the...

trailer emergency brakes to come on Signup and view all the answers

You are uncoupling a trailer. After you shut off the trailer air supply and lock the trailer brakes, you should...

back up gently and ease pressure on the fifth wheel locking jaws Signup and view all the answers

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

never Signup and view all the answers

The front trailer supports are up, and the trailer is resting on the tractor. Make sure that...

there is enough clearance between the tractor frame and the landing gear Signup and view all the answers

Study Notes

Stopping Distance

A fully loaded trailer requires the shortest stopping distance compared to empty or lightly loaded trailers.

Air Leakage Rate

The acceptable air leakage rate for a combination vehicle (engine off, brakes on) should not exceed 4 psi per minute.

Importance of Final Air Brake Check

Skipping the final air brake check can lead to a potential loss of brakes while driving.

Kingpin Locking

The locking jaws should securely close around the shank of the kingpin.

Glad Hands Function

Glad hands are crucial for connecting the service and emergency air lines from the truck to the trailer.

Rollover Risk

Fully loaded trucks are ten times more likely to roll over in a crash compared to empty rigs.

Center of Gravity

A higher center of gravity increases the likelihood of a truck turning over during maneuvers.

Trailer Breakaway Scenario

If the trailer breaks away, the tractor protection valve will close, preventing air pressure loss in the tractor.

Shut-off Valve in Doubles

The shut-off valve that must be closed in the last trailer of a doubles setup is the back section.

Fifth Wheel Locking Lever

If the fifth wheel locking lever is not locked after the jaws close, it indicates that the coupling is incorrect and needs to be addressed before proceeding.

Gear Position after Uncoupling

After uncoupling the trailer and during inspection, the tractor engine should be in neutral.

Trailer Brake Testing

Testing trailer brakes involves applying and releasing them while listening for audible brake sounds to ensure proper operation.

Addressing Brake Release Issues

If trailer brakes do not release, check the air line connections rather than crossing the air lines.

Major Leak in Service Line

A major leak in the service line will trigger the trailer emergency brakes to engage when brakes are applied.

Uncoupling Procedure

When uncoupling a trailer, after shutting off the trailer air supply, it is important to back up gently to relieve pressure on the fifth wheel locking jaws.

Hand Valve Usage

The hand valve should never be used to park a combination vehicle.

Clearance Checks

Ensuring adequate clearance between the tractor frame and landing gear is critical when the front trailer supports are lifted and the trailer rests on the tractor.

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Description

Test your knowledge on combination vehicles with this CDL practice test. The quiz covers essential topics such as stopping distances and air leakage rates, crucial for drivers operating combination vehicles. Perfect for anyone preparing for their CDL exam.