North Dakota CDL: Air Brakes Practice Test

Not quite. The answer is release the spring brakes.

Even after loss of air pressure has caused the spring brakes to come on, you may need to move the vehicle again in an emergency. Some vehicles such as buses have a separate air tank that can be used to release the spring brakes. You can then move the vehicle, after which you can set the spring brakes again. This action is controlled by dual parking control valves: One valve lets air flow from this air tank to release the spring brakes, and the other valve sets them again.

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 a yellow lamp on the left side.

A converter dolly with antilock brakes is required to have a yellow ABS lamp on its left side. All converter dollies built since March 1, 1998 have antilock brakes.

Not quite. The answer is It is exhausted from the system.

Each time you release the brakes, some compressed air leaves the system and must be replenished by the air compressor.

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 air pressure.

Spring brakes contain powerful springs that are normally held back by air pressure. If the pressure drops too low, the spring brakes will automatically kick in.

Not quite. The answer is 5 mph slower.

On a steep downgrade, don't keep applying your brakes continuously because this might cause them to fade (become less effective). Instead, apply your brakes sparingly as a supplement to engine braking. Select a "safe" speed. Let your vehicle reach this speed. Brake gently until you are going 5 mph slower. Then let your speed increase back to the "safe" speed. Keep varying your speed up and down this way. This technique is known as snub braking or snubbing.

Not quite. The answer is The one-way check valve

Federal regulations require a one-way check valve or an equivalent device to be located at the entrance to the first air tank. (In a dual air brake system, there must be a one-way check valve at the entrance to both the primary and secondary air tanks.) If the air compressor or the line connecting it to the air tank develops a leak, the one-way check valve will prevent the air from going out. (Note: The North Dakota Commercial Drivers License Manual does not discuss this topic.)

Source: 49 CFR § 571.121

Not quite. The answer is 60 - 55 psi.

The low air pressure warning light must come on before the air pressure falls below 60 - 55 psi. On some vehicles, the warning light will come on at a higher air pressure. Check the manufacturer's specifications.

Not quite. The answer is Stop and park safely.

If the low air pressure warning comes on, there may be a leak in the system. Pull over and park your vehicle as soon as possible. If the air pressure drops too low, the spring brakes will come on automatically, which will stop your vehicle – but not necessarily in a safe way. Sudden application of the spring brakes while you're driving might result in a skid.

Not quite. The answer is a loss of brake air pressure.

Each time you release the brakes, some compressed air leaves the system and must be replenished by the air compressor. If you keep pressing and releasing the brake pedal, air may leave the system faster than the air compressor can replenish it. The air pressure may drop to the point that the brakes won't work.

Not quite. The answer is Tap on the brake drums.

If a brake lining has gotten frozen to the brake drum, you should be able to free it by using a hammer to tap on the drum near the brake lining. Be careful not to hit the brake lining because you might damage it. Note that you may also need to free the other brake lining in that drum brake. If the valves or other parts of the air braking system are frozen, you may be able to get them unstuck by putting commercial air brake antifreeze (NOT pure methyl alcohol) into the trailer air supply (red) line. However, this will not free frozen brake linings.

Not quite. The answer is forces the brake shoes against the inside of the brake drum.

When the S-cam rotates, it forces the brake shoes apart and against the inside of the brake drum. Friction will slow the rotation of the wheel.

Not quite. The answer is It won't allow the brakes to cool.

Brakes use friction to convert the kinetic energy of your vehicle into heat. Overuse of the brakes won't allow enough time for the brakes to cool. Excessive heat can cause expansion of the brake drums and chemical changes in the brake lining that will reduce friction. The brakes will fade (become less effective).

Not quite. The answer is the brakes when you depress the brake pedal during normal driving.

Air brakes are actually three braking systems in one: the emergency brake, the parking brake, and the service brake. As these terms suggest, when you depress the brake pedal in normal driving, it's the service brake system that applies the brakes.

Not quite. The answer is To avoid injury from high-pressure air and debris

Compressed air may be exhausted from several different ports in the air braking system. This air travels at a very high speed from the vehicle and carries moisture, oil, dirt, and dust. It can be dangerous if it hits your eyes or ears. Know the location of all air exhaust ports so you can keep away from them, such as when you're draining the air tanks.

Not quite. The answer is With ABS, you do emergency braking differently than without ABS.

Without ABS, hard braking can lock the wheels, resulting in a skid. Therefore, to do emergency braking without ABS, you should use the "stab braking" method or the "controlled braking" method. With ABS, go ahead and brake hard; the ABS computer will prevent your wheels from locking.

Not quite. The answer is The heavier the vehicle or the faster it's traveling, the more heat the brakes have to absorb to stop it.

Brakes use friction to convert the kinetic energy of your vehicle into heat. A vehicle's kinetic energy is directly proportional to its weight and directly proportional to the square of its speed. If you increase your speed, your brakes will have to absorb much more heat to bring your vehicle to a stop.

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 turn off the engine, release the parking brake, and let the system settle.

To test for an air leak, turn off the engine, release the parking brake (i.e., push the parking brake control knob in), and see how fast the air pressure drops. The air pressure should drop less than 2 psi in one minute for a single vehicle and less than 3 psi for a combination vehicle.