Illinois CDL: Combination Vehicles Practice Test

Not quite. The answer is back up gently to ease pressure on the fifth wheel locking jaws.

When uncoupling, ease pressure on the fifth wheel locking jaws by backing up gently. (This will help you release the fifth wheel locking lever.) Then apply the parking brakes while the tractor is pushing against the kingpin.

Not quite. The answer is hang it with the plug down.

After you disconnect the electrical cable, hang it with the plug down to keep moisture or rain from getting into it.

Not quite. The answer is it will be raised slightly when the tractor is backed under it.

Before backing the tractor under the trailer, adjust the landing gear to position the trailer at the proper height. The trailer should be just low enough that it will be raised slightly by the tractor when the tractor backs under it. If the trailer is too low, the tractor may hit and damage the trailer nose; if it's too high, it may not couple properly.

Not quite. The answer is there is less traction.

Trucks that are empty or only lightly loaded take longer to stop because the stiff suspension springs and strong brakes give poor traction and make it easier to lock the wheels.

Not quite. The answer is they are more likely to get stuck on raised railroad crossings.

The two types of combination vehicles most likely to get stuck at a raised railroad crossing are low-slung units (car carriers, lowboys, moving vans, etc.) and single-axle tractors that are pulling a long trailer with its landing gear set to accommodate a tandem-axle tractor. Be very careful when driving such vehicles at railroad crossings.

Not quite. The answer is often do not have spring brakes.

Trailers and converter dollies built before 1975 are not required to have spring brakes. Instead, they rely on emergency brakes that hold using air pressure. Because air pressure can leak away, always use wheel chocks when parking such vehicles.

Not quite. The answer is easier it is to turn over.

When you stack cargo high in a trailer, you raise its center of gravity, which makes the trailer more prone to rolling over. A fully loaded tractor-trailer is ten times more likely to roll over in a crash than an empty one.

Not quite. The answer is a Class A CDL with a Doubles/Triples (T) endorsement.

To legally pull a trailer whose gross vehicle weight rating (GVWR) exceeds 10,000 pounds, you'll have to obtain a Class A CDL. To pull triples, you'll also have to obtain a Doubles/Triples (T) endorsement on your CDL. Note: If you don't also pass a knowledge test on air brakes, your CDL will include a restriction limiting you to driving only vehicles without air brakes.

Not quite. The answer is 20 to 45 psi.

The tractor protection valve keeps air in the tractor or truck brake system should the trailer break away or develop a bad leak. The tractor protection valve is designed to close automatically when the air pressure falls into the range specified by the manufacturer, typically 20–45 psi.

Not quite. The answer is straight stretches of highway.

Because of the risk of rollover, you should drive slowly in the following situations: on-ramps, off-ramps, corners, and quick lane changes. Try to avoid fast changes, though.

Not quite. The answer is at normal pressure.

During the coupling process, after you have connected the tractor air lines to the trailer, push in the trailer air supply valve to fully charge the trailer air brake system with compressed air. Make sure that the trailer air brakes are working before you proceed with the rest of the coupling process.

Not quite. The answer is the brakes on the trailer wheels caused the skid in the first place.

The trailer hand valve (also known as a trolley valve or Johnson bar) controls only the trailer brakes, not the tractor brakes. If you're already jackknifing because the trailer wheels locked up, applying the trailer brakes with the hand valve can make it even worse. Instead, stop braking. The rear wheels will start to roll again and you can steer to correct the skid.

Not quite. The answer is the trailer's emergency brakes to come on.

The trailer air supply valve (which is manually controlled by the red dashboard knob) senses air pressure in the supply (emergency) line. If air pressure in the supply line is lost, the trailer air supply valve will close automatically, and the resulting loss of air pressure in the tractor protection valve will cause it to close as well. And loss of pressure in the supply line will cause the trailer emergency (spring) brakes to come on.

Not quite. The answer is ten times as likely to roll over in a crash as empty rigs.

When you stack cargo high in a trailer, you raise its center of gravity, which makes the trailer more prone to rolling over. A fully loaded tractor-trailer is ten times as likely to roll over in a crash as an empty one.

Not quite. The answer is Gently pull forward in low gear against the locked trailer brakes; then look at it carefully.

After you've backed under the trailer and locked the kingpin into the fifth wheel, raise the landing gear slightly. Then with the trailer brakes still locked, gently pull the tractor forward to check that the trailer is locked onto the tractor.

Not quite. The answer is All of the above

The two types of combination vehicles most likely to get stuck at a railroad crossing are low-slung units (car carriers, lowboys, moving vans, etc.) and single-axle tractors that are pulling a long trailer with the landing gear set to accommodate a tandem-axle tractor. Be very careful when driving such vehicles at railroad crossings.

Not quite. The answer is turn the crank a few more times to lift some weight off the tractor.

After the landing gear has made firm contact with the ground, turn the crank in low gear a few more times to take some weight off the tractor, but not so much that you lift the trailer off the fifth wheel. This will make it easier to unlatch the fifth wheel and couple the trailer the next time.

Not quite. The answer is Rear

The shut-off valve should be closed only at the rear of the last trailer so that air will flow to the brakes of all trailers but no farther.

Not quite. The answer is see it in your mirrors.

The earliest way to notice that your trailer is jackknifing is to see it swinging out in your mirrors.

Not quite. The answer is Both of these statements are true.

The trailer hand valve (also known as a trolley valve or Johnson bar) controls only the trailer brakes, not the tractor brakes. You can use it to test the trailer brakes. Don't use it while you're driving, though. If you apply it while you're driving, you'll brake the trailers but not the tractor, which can cause a skid. Instead, use the foot brake, which sends air to the tractor brakes as well as the trailer brakes.