Arizona CDL: Air Brakes Practice Test

Not quite. The answer is spring brakes.

In some vehicles, a control handle on the dashboard may be used to apply the spring brakes gradually. This is called a modulating valve. It is spring-loaded so you have a feel for the braking action. The more you move the control lever, the harder the spring brakes come on. They work this way so you can control the spring brakes if the service brakes fail. When parking a vehicle with a modulating control valve, move the lever as far as it will go and hold it in place with the locking device.

Not quite. The answer is All of the above

Brake fade and failure are usually due to incorrect use of the brakes that causes excess heat. This may be caused by incorrect brake adjustment, not enough reliance on engine braking, excessive use of the service brakes, another mechanical factor, or human error.

Not quite. The answer is It is shaped like the letter "S."

The S-cam really is S-shaped. As it rotates, it forces the brake shoes away from each other and toward the inside of the brake drum.

Not quite. The answer is let the air out of the brake chambers.

The parking brake control allows you to evacuate air from the brake chambers. With the air gone, the spring brakes will come on automatically and hold your vehicle in place.

Not quite. The answer is Radio signal system

The air brakes are made up of three systems: the service brake, the parking brake, and the emergency brake. Before your knowledge test, review the Arizona Commercial Driver License Manual to familiarize yourself with what each one does.

Not quite. The answer is Overheating, low air pressure, and not relying on the engine braking effect

Brake fade and failure are usually due to incorrect use of the brakes that causes overheating. This may be caused by incorrect brake adjustment, not enough reliance on engine braking, excessive use of the service brakes, another mechanical factor, or human error. Air brakes will also fail if air pressure drops too low.

Not quite. The answer is To prevent a buildup of ice in the air brake system

When the air compressor runs, an alcohol evaporator puts alcohol vapor into the air brake system to help prevent water in the lines or valves from freezing. Ice in the lines or valves can cause them to stop working.

Not quite. The answer is when air is pumped into the air storage tanks.

The air compressor runs at all times while the engine is running. To keep the air pressure from eventually rising too high, the air compressor governor controls when the compressed air from the air compressor should flow into the air reservoirs. When air pressure drops to a certain level (typically 100 psi), the governor "cuts in" and routes the compressed air into the storage tanks. When air pressure rises to a certain level (typically 125 psi), the governor "cuts out" and routes the compressed air out of the system, into the atmosphere.

Not quite. The answer is S-cam drum brake.

Foundation brakes are present on each wheel. In North America as of this writing, S-cam drum brakes are much more common than wedge or disc brakes.

Not quite. The answer is 2 psi per minute.

One of the tests you must make of the air brake system is a test of the leakage rate without the foot brake applied. Fully charge the air brake system, turn off the engine, and release the parking brake. The air pressure should not drop more than 2 psi per minute for a straight vehicle or 3 psi per minute for a combination vehicle. If it is greater, check for leaks in the system.

Not quite. The answer is you have to press the brake pedal harder than usual to control your speed.

If your brakes begin to fade, you'll notice that you have to depress the brake pedal harder to achieve the same braking effect as before. If your vehicle is so equipped, check the application pressure gauge to see just how much pedal effort you are employing. If the brakes continue to fade, you may not be able to slow down or stop at all.

Not quite. The answer is More than 400 feet

The stopping distance equals the sum of the perception distance, reaction distance, brake lag distance, and braking distance. Under ideal conditions, the average driver of a bus or large truck equipped with air brakes and traveling at 55 mph would require about 451 feet to come to a complete stop. The length of a football field including the two end zones is 360 feet.

Not quite. The answer is Ice may form in the air storage tanks and cause the brakes to fail.

Moisture in the warm, compressed air from the air compressor will condense as the air cools. In below-freezing temperatures, this moisture can freeze. Ice in the tanks and air lines can cause the brakes to stop working. Whenever the air compressor runs, the alcohol evaporator puts alcohol vapor into the air brake system to help prevent water in the lines or valves from freezing. (Alcohol has a lower freezing point than water.)

Not quite. The answer is a supply pressure gauge.

Every vehicle with air brakes has a supply pressure gauge, which shows how much air pressure is in the air tanks. Some vehicles also have an application pressure gauge, which shows how much air pressure you are applying to the brakes. Older vehicles also had a manual front brake limiting valve, which allowed the driver to cut front brake air pressure in half as a way of preventing front-wheel skids. However, tests have shown that full front-wheel braking is safe.

Not quite. The answer is 3,000 pounds.

The most common type of air brake chamber in trucks and trailers is the Type 30. The type number gives the area of the diaphragm. Thus, the diaphragm in a Type 30 brake chamber has an area of 30 square inches. If a force of 100 psi (pounds per square inch) is applied to the diaphragm, the resulting pushrod force will equal 100 × 30 = 3,000 pounds.

Not quite. The answer is your vehicle will stay in a straight line.

If you must brake in an emergency, brake in a way that keeps your vehicle in a straight line while still letting you turn if necessary. You can use the "controlled braking" method or (in a vehicle without antilock brakes) the "stab braking" method.

Not quite. The answer is a supply tank.

An Integrated Solution Air Dryer (AD-IS®) and Reservoir System provides an integrated air dryer, purge reservoir, governor, and a number of the charging valve components in a module. The air dryer is so efficient that a supply ("wet") tank is not needed. Instead, the AD-IS sends air directly to the primary and secondary service ("dry") tanks.

Not quite. The answer is a Class A CDL without an air brakes restriction.

To legally pull a trailer whose gross vehicle weight rating (GCWR) exceeds 10,000 pounds, you'll have to obtain a Class A CDL. If you don't pass a knowledge test on air brakes, your CDL will include a restriction limiting you to driving only vehicles without air brakes.

Not quite. The answer is expansion of the brake drums.

Overusing the service brakes can cause overheating and expansion of the brake drums. The brake shoes will have to move farther to contact the brake drums, making braking harder or eventually impossible (brake fade).

Not quite. The answer is 60

The low air pressure warning light must come on before the air pressure falls below 60 psi. On some vehicles, the warning light will come on at a higher air pressure. Check the manufacturer's specifications.