Oklahoma CDL: Combination Vehicles Practice Test

Not quite. The answer is Always

If there is a leak in the emergency air line, air will eventually leak out of the trailer air tank. If the trailer has air brakes but not spring brakes, the brakes will fail. Use chocks to prevent the trailer from rolling if its brakes fail.

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 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 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 applying and releasing the trailer brakes and listening for brake sounds.

After you've connected the air lines, double-check the connection and make sure the brakes are working. Shut off the engine so you can hear the brakes. Apply the brakes and listen for the sound of the brakes being applied. Release the brakes and listen for the hiss of escaping air.

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 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 two red lights

According to federal regulations, if the load projects more than 4 feet behind the rear of the vehicle, the end of the load must be marked as follows: (1) with two red flags, each 18 inches square, in the daytime; or (2) with two red lights at night. There are additional federal requirements on how to illuminate the rest of the load. US states may impose their own additional requirements on the transportation of oversized loads. You can learn about Oklahoma's requirements by contacting the Oklahoma Department of Public Safety or visiting their webpage "Chapter 30 – Size and Weight Permits" (https://www.ok.gov/dps/Administrative_Rules/Size_and_Weight_Permits/index.html). [49 CFR 393.11],

Source: 49 CFR 393.87

Not quite. The answer is makes firm contact with the ground and takes some weight off the tractor.

When uncoupling a loaded trailer, lower the landing gear until it makes firm contact with the ground. Then crank the landing gear in low gear for a few more turns – just enough to lift 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 now and couple next time.

Not quite. The answer is more

There are more things to inspect on a combination vehicle than on a bus or straight truck. First, of course, there is the entire coupling system: the kingpin, the fifth wheel, etc. Next, there is the landing gear of each trailer. Finally, the air brake system is also more complicated than on a bus or straight truck, because compressed air must flow to all trailers so that both the tractor brakes and trailer brakes will work properly.

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 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 It should not be done.

The trailer hand valve (also known as a spike, a trolley valve, or a Johnson bar) controls only the trailer brakes, not the tractor brakes. If you apply it while you're driving, you'll brake the trailers but not the tractor. This can cause a trailer skid.

Not quite. The answer is To engage the trailer brakes in case of air pressure loss

The emergency air line has two main functions: (1) It supplies air to the trailer air tanks to keep the trailer brake system charged. (2) It controls the vehicle's emergency brakes. If air pressure in the emergency air line drops too low (say because of a bad leak or damage due to the trailer breaking loose), 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 emergency

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 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 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 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 20 to 45 psi.

The tractor protection valve is located in the tractor, usually at the rear of the cab. Its purpose is to keep air in the tractor's air brake system should the trailer break away or develop a bad leak. The tractor protection valve is designed to close automatically if the air pressure falls into the range specified by the manufacturer, typically 20–45 psi.

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.