Wisconsin CDL: Combination Vehicles Practice Test

Not quite. The answer is service and emergency air lines from the truck or tractor to the trailer.

Each glad hand has a rubber seal to prevent air from escaping. To connect the glad hands, first clean the seals. Then press the two seals together with the glad hands at a 90-degree angle to each other.

Not quite. The answer is 90 degrees

When connecting the glad hands, press the two seals together with the couplers at a 90-degree angle to each other. A turn of the glad hand attached to the hose will join and lock the couplers.

Not quite. The answer is empty.

The weight of a full load adds traction. An empty or lightly loaded trailer is more likely to jackknife than a fully loaded one.

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

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.

Not quite. The answer is to the driver's side.

If you must back your vehicle on a curved path, back toward the driver's side. You'll be able to watch the rear of your vehicle from your driver's-side window.

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 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 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 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 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 It will keep dirt and water out of the lines.

Some vehicles are equipped with "dead-end" or dummy couplers. When the air lines are not connected to a trailer, connect the glad hands to the dummy couplers to keep water and dirt out of the glad hands and air lines. If your vehicle doesn't have dummy couplers, you may be able to connect the glad hands to each other.

Not quite. The answer is Control line and signal line

The service air line is also known as the control line or signal line.

Not quite. The answer is A 3-axle tractor towing two 27-foot trailers

When any vehicle turns, its rear wheels will follow a shorter path than its front wheels. This is called off-tracking or "cheating." The longer the vehicle, the greater the difference. In a combination vehicle, the trailer's wheels will off-track more than the tractor's rear wheels. In a double or triple combination vehicle, the wheels of the last trailer will off-track the most.

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 whether it is on the tractor or the trailers.

ABS can help prevent wheel locking regardless of whether it's on the tractor, the trailer, or both.

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 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 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 get away from your vehicle and call 911 or the posted emergency number.

A train traveling at 60 mph can take more than a mile to come to a complete stop. If your vehicle gets stuck on a railroad track, don't spend any time trying to free your vehicle. Get out of your vehicle and walk quickly at about a 45-degree angle to the tracks in the direction from which you expect trains to approach. That way, if your vehicle is hit, you won't be struck by flying debris. Call 911 or the telephone number on the railroad crossing sign for assistance.

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.