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Practice for your Combination Vehicles CDL exam with questions based on the official South Carolina CDL handbook
If you are not pulling a trailer, why should you lock the truck gladhands together (or use dummy couplers)?
When you're not pulling a trailer, connecting the glad hands together or to dummy couplers helps keep dirt and water out of the air lines. This keeps the lines clean and ready for when you need to hook up to a trailer again.
For a coupling to be properly done, the safety latch on the fifth wheel locking lever must be _____.
The right way to hook up the fifth wheel locking lever for it to be safe and right is for the safety latch to be over the locking lever.
What is the proper position for the fifth wheel when coupling with a trailer?
When connecting the trailer to the truck, the fifth wheel (the part that connects them) should be tilted down towards the end of the trailer. This position helps hook up the trailer securely.
After coupling the trailer with the truck, in what position should the truck protection control valve be set?
After hooking up a trailer to a truck, the valve that helps control the brakes should be set to the 'normal' position. This makes sure the brakes work right when needed.
What is correct out of the following?
Bobtail tractors without a trailer can actually take longer to stop compared to when they are pulling a fully loaded trailer. This is because the weight helps push the brakes down more effectively.
Where should the truck be when you uncouple the trailer and inspect the landing gear?
After you disconnect the trailer, park your truck straight under the trailer, not to the side or at an angle. This way, you're in the right spot to check the landing gear safely and properly.
After you hook up the air lines, but before you back up under the trailer, you should:
After you connect the air lines, before you move your truck under the trailer, you need to make sure the trailer's air system is working. Do this by sending air into the trailer's system and then pulling the knob that controls the air supply. This ensures the brakes and other systems are ready to safely operate.
When operating a combination vehicle, the trailer unexpectedly disconnects, causing both air lines to separate. In addition to the trailer brakes coming on, you expect:
When the trailer comes off and air lines break, special valve shuts to keep air in the truck's brakes, ensuring it can still be controlled.
You're getting ready to reverse your truck under a semitrailer. The semitrailer is at the correct height when the:
The trailer is at the right height for connecting if it slightly lifts when the tractor backs under it. This means the tractor fits just right, not too high or low, making a secure connection.
The higher the center of gravity of your truck, the:
When your truck's center of gravity is high, it means the truck is more likely to tip over, especially when turning. This doesn't really affect how the brakes work or how fast the truck can speed up.
Why is it necessary to put grease on the fifth wheel plate?
Greasing the fifth wheel plate is crucial because it helps prevent steering problems. Without proper lubrication, the friction between the tractor and the trailer can make steering harder and less smooth. This can lead to difficulties in controlling the vehicle, especially when turning.
When uncoupling the trailer, after you turn off the trailer air supply and make sure the trailer's brakes are set, you should:
After turning off the trailer's air supply and making sure its brakes are locked, you should back up a little bit. This helps reduce pressure on the connection point (fifth wheel) between your truck and the trailer, making it easier to separate them.
A truck pulling a _______ trailer needs the longest distance to stop.
An empty trailer requires more stopping distance because it lacks the weight that typically provides traction during braking. As a result, it takes longer to come to a complete stop compared to a heavily loaded trailer.
When you're driving behind another car in good weather, make sure there's at least one second of space for every ____ feet of your vehicle's length.
When following another vehicle, keep at least 1 second of space for every 10 feet of your vehicle's length. This gives you enough room to stop safely if needed.
When driving a truck with two trailers, which shut-off valve do you have to close on the last trailer?
When driving a truck with two trailers, make sure to close the back valve on the last trailer. This helps keep the air pressure right so your brakes work properly.
When testing a combination vehicle, with the engine turned off and the brakes applied, the air shouldn't leak out faster than _____ psi every minute.
For a big vehicle with multiple parts, like a truck pulling a trailer, when it's not running and the brakes are applied, the air pressure in the brakes shouldn't drop more than 4 psi in a minute. This ensures the brakes stay strong and can stop the vehicle safely.
Trailers with air brakes made before 1975:
Trailers with air brakes made before 1975 don't need to have a special system (ABS) to stop wheels from locking when braking. They also don't have to have spring brakes, which can automatically apply brakes if there's a problem. These trailers need their brakes adjusted by hand.
For a combination vehicle that uses air brakes, when the engine is off and the brakes are off, the air brake leakage rate should not be more than ____ psi every minute.
When checking if the air brakes on a big truck and trailer are leaking too much (with the engine off and not using the brakes), it's okay if the air pressure drops a little, but not more than 3 pounds per square inch (psi) every minute.
How can you stop a trailer from skidding?
If your trailer starts to skid, quickly let go of the brakes. This helps your wheels start rolling again and gets the trailer back under control.
There are two ways a driver can stop a truck from rolling over. They are: (1) put the load as low as possible and (2):
To stop a truck from tipping over, do two things: 1) Load stuff low down to keep it stable. 2) Take corners slowly. This way, the truck is more balanced and less likely to fall over.
The Combination Vehicles test is required for anyone seeking a Class A CDL in South Carolina. It covers coupling and uncoupling procedures, rollover prevention, inspecting combination vehicles, and safely operating with attached trailers.
The Combination Vehicles test is part of the CDL written exam administered by the South Carolina Department of Motor Vehicles. You must pass this test along with the other required written tests to receive your Commercial Learner's Permit (CLP) in South Carolina.
Our practice questions are built from the official South Carolina CDL handbook and federal FMCSA regulations. Each question includes a detailed explanation to help you understand the material, not just memorize answers.
