CDL Combination Vehicles Practice Test 3

Question 1

When coupling a tractor to a semi-trailer, what is the correct order for connecting the air lines?

Accepted Answer

Connect the emergency (red) line first, then the service (blue) line

Answer

Connect the service (blue) line first, then the emergency (red) line

Answer

Connect both lines simultaneously to avoid pressure loss

Answer

Order does not matter as long as both lines are connected before moving

Question 2

What is the purpose of a converter dolly in a double or triple combination?

Accepted Answer

It converts the lead trailer's kingpin into a fifth-wheel coupling for connecting an additional trailer

Answer

It provides extra braking power for the rear trailers

Answer

It acts as an additional power unit when ascending steep grades

Answer

It houses the air tanks for the rear trailer's braking system

Question 3

What should you do if a trailer's air supply valve is in the 'emergency' position during a pre-trip inspection?

Accepted Answer

Push it in to restore air supply before moving the vehicle

Answer

Leave it as-is; the emergency position is normal for parked trailers

Answer

Connect a portable air tank and drive slowly to a service center

Answer

Disconnect the air lines and reconnect them to reset the valve

Question 4

When uncoupling a combination vehicle, which action must you take BEFORE lowering the landing gear?

Accepted Answer

Apply the tractor parking brakes and chock the trailer wheels

Answer

Disconnect the electrical cable and then the glad hands

Answer

Back under the trailer to relieve kingpin tension

Answer

Raise the fifth-wheel locking jaw to the unlocked position

Question 5

When inspecting the pintle hook connection between a converter dolly and a trailing unit, you should verify that:

Accepted Answer

The latch is fully closed and the safety latch or lock is engaged

Answer

The pintle hook is lubricated with chassis grease before every trip

Answer

The pintle hook ring has at least 1 inch of free play to allow turns

Answer

The draw bar eye is made of a lighter metal than the hook to act as a breakaway

Question 6

What is 'crack-the-whip' effect in a double or triple combination, and how do you reduce the risk?

Accepted Answer

Rearward amplification of sway that can flip rear trailers; reduce speed before curves and avoid abrupt steering

Answer

Sudden jackknifing of the lead trailer caused by over-braking; pump the brakes instead of hard braking

Answer

Air pressure spikes that blow the rear trailer's tires; reduce speed on long downgrades

Answer

Electrical surges from the trailer harness; keep speed below 45 mph at all times