Utah CDL: Combination Vehicles Practice Test

Not quite. The answer is open except for those on the last trailer.

The shut-off valves are located at the rear of each trailer to allow you to stop the air flow there. If there is another trailer behind this one, open the valves to allow air to flow to that trailer; otherwise, close the valves.

Not quite. The answer is Fully raised with the crank handle secured in its bracket

Once you've coupled, raise the landing gear all the way up. If it's only partially raised, it could catch on something, such as the railroad tracks on a raised railroad crossing.

Not quite. The answer is To prevent steering problems

One of the first steps in coupling a tractor to a trailer is to check that the fifth wheel skid plate is greased as required. If the fifth wheel plate is not properly lubricated, friction between the plate and the trailer apron could cause steering problems.

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 at normal pressure.

Before backing under a trailer during the coupling process, make sure that the air pressure is at normal levels so you'll be able to brake safely.

Not quite. The answer is It is used to supply the trailer with air, shut the air off, and apply the trailer emergency brakes.

On newer vehicles, the trailer air supply control is an eight-sided red knob on the dashboard of the tractor. The knob may be labeled "Pull to exhaust...Push to supply" or something similar. When you push the knob in, air will flow through the trailer's emergency air lines to charge the trailer air brake system. Pulling out the knob shuts off the flow of air and causes the trailer emergency brakes to come on.

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.

Not quite. The answer is Turn wide as you complete your turn.

To turn right, you may need to turn wide to help prevent the rear end of your vehicle from overrunning the curb. However, if you swing wide to the left before you turn right, another driver may try to pass you on your right, which can lead to a collision. Instead, start the right turn with the rear of your vehicle as close to the curb as possible and then turn wide as you complete the turn. This will deny drivers room on the right to try to pass you.

Not quite. The answer is tilted down toward the rear of the tractor.

Before coupling, make sure that the fifth wheel is in the proper position. For one thing, it should be tilted down toward the rear of the tractor so that the trailer can easily slide into it.

Not quite. The answer is the coupling is not right and should be fixed before you drive the coupled unit.

Don't drive the vehicle until you're sure that the coupling is correct. Check to make sure of the following: There is no space between the upper and lower fifth wheel, the fifth wheel jaws have closed around the shank of the kingpin, the locking lever is in the "lock" position, and the safety latch is in position over the locking lever. If anything isn't right, don't drive the vehicle until you've found and corrected the problem. If you drive it anyway, your trailer could come loose while you're driving.

Not quite. The answer is "Bobtail" tractors can take longer to stop than a combination vehicle loaded to the maximum gross weight.

When a combination vehicle is empty or lightly loaded, its braking distance increases. The very stiff suspension springs and strong brakes give poor traction and make it very easy to lock the wheels. Likewise, "bobtail" tractors (tractors without semitrailers) can take longer to stop than a fully loaded tractor-trailer. Be very careful when driving a "bobtail" tractor.

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

If air pressure in the emergency air line drops too low (say because of a bad leak in the service line), the trailer emergency brakes will come on. Also, the tractor protection valve will close to keep air from escaping from the tractor.

Not quite. The answer is there is enough clearance between the tractor frame and the landing gear to accommodate sharp turns.

After you've coupled the trailer and fully raised the landing gear, check that there is enough clearance between the rear of the tractor frame and the landing gear so they won't make contact even on sharp turns.

Not quite. The answer is always use the lowest reverse gear.

When coupling, use the lowest reverse gear and back slowly to avoid hitting or damaging the kingpin.

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 Drive normally and get it fixed later.

Losing the ABS function does not change the basic parts of your truck, so you will still have the same brakes that you have always had. Simply use them and get the ABS repaired as soon as possible. There is no need to panic, unless your system shows other and more serious warnings.

Not quite. The answer is Nothing is likely to happen until you try to apply the brakes.

If a leak has developed in the service line, air tank pressure may remain close to normal – until you try to brake. Then the air loss from the leak will cause the air pressure to drop quickly. If the air pressure drops far enough, the emergency brakes will come on.

Not quite. The answer is low gear.

Start to raise the landing gear by using the low gear range (if the landing gear is so equipped). Then switch to the high gear range once the trailer supports are free of weight.

Not quite. The answer is emergency line

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 Normal

To test the trailer air brake system, first charge it with air. Push in the red trailer air supply knob, or place the tractor protection valve control in the "normal" position. Wait until the air pressure reaches normal before you start your tests.