New Hampshire CDL: Air Brakes Practice Test

Not quite. The answer is The brakes could fail.

Water and oil from the compressor can collect at the bottoms of the air tanks. If the air tanks are not drained regularly, the water and oil can freeze or coagulate and cause brake failure.

Not quite. The answer is If the brakes are very hot

If the brakes are too hot, avoid using the parking brakes because the heat may warp and damage the brakes. Also avoid using the parking brakes if they are wet and at risk of freezing. If the parking brakes freeze, your vehicle will be immobilized. In both of these situations, use wheel chocks instead.

Not quite. The answer is Turn the adjusting nut to move the end of the slack adjuster until the brake shoes contact the inside of the brake drum. Then turn the nut the other way to move the brake shoes away from the brake drum.

To adjust a manual slack adjuster, turn the adjusting nut so that the S-cam rotates in the same direction as when the brakes are applied. Keep turning the nut until the nut stops turning. At this point, the brake shoes should be pressing tight against the inside of the brake drum. Then turn the nut the other way about one-third of a turn to move the brake shoes away from the inside of the brake drum. Note: This procedure may not be described in your CDL manual.

Not quite. The answer is Every time you leave your vehicle, with a few exceptions

You should always use your parking brake except when the brakes are very hot or they are wet and at risk of freezing.

Not quite. The answer is the emergency brake system.

The system that uses parts of the service and parking brake systems to stop the vehicle in a brake system failure is called the emergency brake system.

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 your brakes may fail because of water freezing.

Your air tanks hold a mixture of water and compressor oil. If left inside to collect at the bottom, the water may freeze and cause brake failure.

Not quite. The answer is press the brake pedal as hard as you can, release the brakes when the wheels lock, and apply the brakes again when the wheels start to roll.

To stop with stab braking, brake hard, release the brakes once the wheels lock, and then brake hard once the wheels start to roll again. (Note that this method won't work if your vehicle has antilock brakes, because the wheels won't lock. Use controlled braking instead.)

Not quite. The answer is the brakes to fade.

Excessive heat caused by overuse of the brakes can expand the brake drums away from the brake pads or shoes and affect the brake linings, reducing friction. The brakes will fade (lose their effectiveness). On a long or steep downgrade, rely on engine braking more than the service brakes.

Not quite. The answer is All of the above

A modern Air Dryer Integrated System (AD-IS) combines the governor, air dryer, and safety valve into one system. Compressed air from the air compressor goes to the AD-IS, which removes moisture and contaminants from the air. The clean, dry air then goes to fill the primary and secondary service tanks.

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 about 250 °C.

Brakes are designed to withstand quite a lot of heat. The brake components can withstand temperatures up to about 250° C (482 °F) under hard braking.

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 Leaky glad hand seals

Glad hands have rubber or urethane seals to form a tight connection and prevent air from escaping. The glad hands are constantly being connected and disconnected, so the seals tend to wear out over time. Leaky seals can cause loss of air pressure.

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 by increasing and decreasing the air pressure.

The air compressor governor should cut in when a lower air pressure is reached and cut out when a higher air pressure is reached. (Check your manufacturer's specifications for these pressures.) To test this, run the engine at a fast idle to raise the air pressure until the air compressor governor cuts out. Then keep stepping on and off the brake pedal to reduce the air pressure until the air compressor governor cuts in.

Not quite. The answer is 3 psi for single vehicles and 4 psi for combination vehicles.

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

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 All weather conditions

Front wheel brakes have been shown to be ideal under all weather and driving conditions. Front wheel braking is unlikely to cause a skid even on icy roads.

Not quite. The answer is 150 psi

The safety valve, which protects the system from excessive pressure, is usually set to open when the system reaches 150 psi.