West Virginia CDL: Combination Vehicles Practice Test

Not quite. The answer is 4 psi per minute.

After the initial drop, the maximum acceptable leakage rates with the service brakes on are 3 psi per minute for single vehicles and 4 psi per minute for combination vehicles. If the leakage rate is higher, check for leaks and correct them.

Not quite. The answer is your brakes might fail.

On a combination vehicle, the brakes on the tractor and all trailers must work properly. If your combination vehicle is equipped with air brakes, check that air flows to all trailers and test both the trailer service brakes and the trailer emergency brakes.

Not quite. The answer is make sure the ground is solid and can support the weight of the trailer.

Before uncoupling the trailer, be sure you're leaving it on firm ground that can support its weight.

Not quite. The answer is Push in the trailer air supply valve control.

The control for the trailer air supply valve is an eight-sided red knob on the dashboard. You push the knob in to supply compressed air to the trailer air brake system. You pull the knob out to evacuate air from the trailer air brake system (which will set the trailer brakes).

Not quite. The answer is spread evenly across the rig and as low as possible.

More than half of truck driver deaths in accidents are the result of truck rollovers. 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. Drive slowly through curves and turns.

Not quite. The answer is emergency

To test the tractor protection valve, shut the engine off and step on and off the brake pedal several times to reduce the air pressure in the tanks. When the air pressure has fallen enough (typically into the range 20–45 psi), the trailer air supply control knob should pop out, or the valve control should go from the “normal” to the “emergency” position.

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 If the trailer has no spring brakes, you will be able to drive away but you won't have trailer brakes.

Trailers built before 1975 are not required to have spring brakes. If you cross the air lines when coupling such a trailer, you may have no air pressure to supply the trailer brakes. You'll be able to drive, but you won't be able to brake the trailer. Always test the trailer air brakes before you start to drive.

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 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 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 supply air to the trailer system and then pull out the air supply knob.

Before you back under the trailer, you must lock the trailer brakes. First, supply air to the trailer air brake system and make sure that the system is working properly. Then set the trailer air supply control to lock the trailer brakes. To do this, pull out the red air supply knob (on newer vehicles) or move the tractor protection valve control to the emergency setting.

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 The trailer emergency brakes will 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 Neutral

Before you inspect the trailer supports of the landing gear, secure the tractor by applying the parking brake and placing the transmission in Neutral.

Not quite. The answer is Never

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. But don't use it as a parking brake, especially if the trailer lacks spring brakes. If a leak causes loss of air pressure, the trailer brakes will fail. Don't use the trailer hand valve while you're driving either. Braking the trailer and not the tractor can cause the trailer to skid.

Not quite. The answer is Bobtail tractors can take longer to stop than fully loaded combination vehicles.

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 the tractor protection valve to close.

The tractor protection valve keeps air in the tractor if the trailer breaks away or develops a bad leak. If air pressure drops too low in the service line, the tractor protection valve will close. This stops air from escaping from the tractor and lets air out of the trailer emergency line, causing the trailer emergency brakes to come on.

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 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.