South Carolina Combination Vehicle CDL Practice Test

The Combination Vehicles CDL practice test contains 20 questions you can expect to find on the South Carolina CDL exam. You will need to know how to operate a combination vehicle which includes tractor-trailer, straight truck, doubles and triples. This includes coupling and uncoupling, connecting air lines, emergency braking and more. Take the test to prepare for the South Carolina Combination Vehicles portion of the CDL test.

You are hooking a tractor to a semi-trailer and have backed up but are not under it. What should you do before backing under the trailer?

Hook up the electrical service cable

Hook up the emergency and service air lines

Connect the ground cable

Nothing. Back up and secure the fifth wheel to the trailer

None

After pushing in the trailer supply valve, you should not move the tractor until the whole air system is

Charging

At normal pressure

Bled down to half the maximum pressure

Between 50 and 60 psi

None

There are two things that a driver can do to prevent a rollover. They are (1) Keep the cargo as close to the ground as possible, and (2)

Make sure that the brakes are adjusted properly

Keep both hands firmly on the steering wheel

Drive slowly around turns

Keep the fifth wheel free-play loose

None

With the engine off and the brakes released, a combination vehicle air brake system should not leak more than how many psi in one minute?

None

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

The trailer will not swing on the fifth wheel

You cannot set the fifth wheel for proper weight distribution

The hand valve is released and you may drive away

The coupling is not correct and should be corrected before driving the coupled unit

None

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

The hand valve will apply the tractor brakes instead of the trailer brakes

The brake pedal will work the trailer spring brakes instead of the trailer brakes

If the trailer has no spring brakes, you could drive away but you wouldn’t have trailer brakes

The brake lights will not come on when the brake pedal is pressed

None

After coupling a semi-trailer, you should crank up the front trailer supports (dollies) how?

Raised ½ way with the crank handle secured

Raised ¾ way with the crank handle removed

Fully raised with the crank handle secured

Three turns off the top with the crank handle secured in its bracket

None

Air brake equipped trailers made before 1975

Are not required to have spring brakes

Are easier to stop than newer trailers because they are heavier

Usually need a glad hand converter

Cannot be operated on interstate highways

None

The hand valve should be used to park a combination vehicle when?

When you park at loading docks

When you are parking for less than one hour

When parking on a step grade

Never

None

10.

Air lines on a combination vehicle are often colored to keep from getting them mixed up. The emergency line is ______.

Red

Black

Blue

Orange

None

11.

How do you supply air to the air tank on the trailer? You supply air to the trailer tank by

Pushing in the trailer air supply knob/valve

Pulling out the trailer air supply knob/valve

Connecting the emergency line glad hand

Applying the trolley valve

None

12.

In normal driving, some drivers use the trolley (hand) valve before the brake pedal. Which of these statements is true?

It should never be done

It results in less skidding than using the brake pedal alone

It lets the driver steer with both hands

It is the best way to brake in a straight line

None

13.

You are hooking up a tractor and semi-trailer. You have connected both air lines. Before backing under the trailer you should

Pull forward to test glad hand connections

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

Make sure that the trailer brakes are off

Blow the horn twice to alert others

None

14.

When backing up under a trailer, you should line up

About 15 degrees off the line of the trailer

The right mirror along the right edge of the trailer

Directly in front of the trailer

To the far left of the trailer

None

15.

_____ are coupling devices used to connect the service and emergency air lines from the truck or tractor to the trailer.

Clamps

Shut-off valves

Hand valves

Glad hands

None

16.

After hooking up, you should check the fifth wheel connection by

Driving away at 20 mph and pulling down the trailer hand valve

Backing up with the trailer brakes released

Pulling the tractor ahead sharply to release the trailer brakes

Pulling the tractor ahead gently with the trailer brakes locked

None

17.

How often should you drain your vehicle’s trailer air tanks.

Daily

Weekly

Monthly

Yearly

None

18.

The emergency air line supplies air to the trailer air tanks and

Supplies air to the cab

Controls the emergency brakes on combination vehicles

Are coded with the color green to keep them from getting mixed up with other lines

All of the above

None

19.

How much space should be between the upper and the lower fifth wheel plates?

About 1 inch

About ½ inch

About ¼ inch

None

20.

When not pulling a trailer, why is it a good idea to lock the glad hands together or to a dummy coupler?

It keeps air from escaping

The brake circuit becomes a secondary air tank

It keeps dirt and water out of the lines

All of the above

None

Great job you’ve finished the Texas Combination Vehicle CDL Practice test! Please enter your name and email. Your results will be presented on the next page. Feel free to retake the test as many times as you need to.

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