New Mexico CDL: Combination Vehicles Practice Test

Not quite. The answer is glad hands

As part of your vehicle inspection test, if your vehicle is equipped with air brakes and has a trailer, you will inspect the air connections between the truck or tractor and the trailer. These connections are made with hose couplers (commonly called "glad hands" because they vaguely resemble shaking hands). These glad hands have rubber seals to form a tight connection and prevent air from escaping. Make sure that the glad hands are locked in place and free of damage or air leaks.

Not quite. The answer is The shank

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 slightly raised.

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 opening the emergency line shut-off valve and then the service line valve at the rear of the last trailer and listening for air escaping each time.

To check whether air is flowing to all trailers, go to the rear of the last trailer and open the emergency line shut-off valve there. If the entire system is charged, you should hear air escaping. Then close that valve and open the service line valve. Again, you should hear air escaping.

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.

Not quite. The answer is empty.

Trucks brake best when they are used as they were designed: to carry a properly balanced load. 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.

Not quite. The answer is keep the cargo as close to the ground as possible.

The higher the truck's center of gravity, the more likely it is to roll over. If the cargo is to one side, it will make the trailer lean, which can also make a rollover more likely. To help prevent a rollover, spread your cargo evenly and keep it as low as possible.

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 a fully loaded trailer

Trucks brake best when they are used as they were designed: to carry a properly balanced load. Empty trucks actually have longer stopping distances than loaded trucks because they have less traction. The stiff suspension springs and strong brakes give poor traction and make it easier to lock the wheels.

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 over the locking lever.

The safety latch should be in position over the fifth wheel locking lever. On some vehicles, you may have to position it manually.

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 Look under the vehicle for the ECU and wheel speed sensor wires coming from the back of the brakes.

You can tell if your vehicle has ABS by looking under the vehicle for the electronic control unit (ECU) and wheel speed sensor wires leading from the back of the brakes.

Not quite. The answer is A triple 27-foot trailer

Because of rearward amplification (causing the crack-the-whip effect), the last trailer in a combination vehicle has the highest probability of rolling over. The last trailer in a triple combination is more likely to roll over than the last trailer in a double combination.

Not quite. The answer is Both (a) and (c)

When the full weight of the trailer is resting on the tractor, check for enough clearance between the landing gear and the rear of the tractor frame. (When the tractor turns sharply, it must not hit the landing gear.) Also check for enough clearance between the tops of the tractor tires and the nose of the trailer. (When the tractor turns sharply, the front part of the trailer must not hit the tractor's tires.)

Not quite. The answer is the brakes will fail if the air supply leaks away.

If the trailer lacks spring brakes, make sure you chock the wheels whenever you park. If air pressure leaks away, the trailer's brakes will fail. Without chocks, the trailer could roll away.

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 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 check the air line connections.

If you cross the emergency and service air lines, air will flow to the service line instead of the trailer air tanks. Air won't be available to release the spring brakes. Therefore, if the spring brakes don't release when you push the trailer air supply control, check the air line connections.

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.