South Dakota CDL: Air Brakes Practice Test

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 are correct.

On both tractor-trailers and single vehicles, to test whether the spring brakes will come on automatically, use the same method you use for testing the low air pressure warning signal: Step on and off the brake pedal, this time until you reach an even lower psi reading and the parking brake valve closes or pops out.

Not quite. The answer is Drive normally until the ABS is repaired.

Losing the ABS function does not change the basic parts of your truck, so you will still have the same brakes that you have always had. Simply use them and get the ABS repaired as soon as possible.

Not quite. The answer is park on level ground, chock the wheels, and release the parking brakes.

Chock the wheels so you can release the parking brakes safely. Then put on gloves and pull hard on each slack adjuster you can reach. If it moves more than about one inch, it needs to be adjusted.

Not quite. The answer is one-half

During your walk-around inspection, check the brake drums to be sure that no cracks are longer than half the width of the friction area.

Not quite. The answer is 125 psi.

A typical air brake system will be fully charged at 125 psi. Check the manufacturer's specifications for the actual figure for your vehicle. The air compressor should stop pumping air at that point.

Not quite. The answer is They are springs that apply the brakes if air pressure drops too low.

Spring brakes are an important backup system: powerful springs that automatically apply the brakes if they sense that air pressure has dropped too low for effective braking. The spring brakes are also used as parking brakes.

Not quite. The answer is release the spring brakes.

When main air pressure is lost, the spring brakes come on and stop your vehicle. Some vehicles such as buses have a separate air tank with enough air to release the spring brakes in case the vehicle must be moved temporarily in an emergency. (The tank holds only enough air to do this a few times, however.) You control this action with the dual parking control valve.

Not quite. The answer is Check if the vehicle was manufactured after 1998.

Vehicles manufactured after 1998 are required to have antilock brakes. They also have a yellow ABS malfunction lamp.

Not quite. The answer is the air pressure may drop too low during driving.

The manufacturer's specifications should state how fast the air pressure should build up once the engine has reached normal operating speed. If the air pressure does not build up fast enough during your final air brake check, the air pressure may not replenish quickly enough during normal braking either. Don't drive the vehicle until the cause has been found and corrected.

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 150 psi

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

Not quite. The answer is braking effect of the engine.

Going down a hill, you should keep your engine in a low gear to keep your speed low, and use the air brakes as a supplemental tool to slow down.

Not quite. The answer is brake drum.

In North America, the most common type of foundation brake is the S-cam drum brake. The brake shoes and linings press against the inside of the brake drum, which causes friction to slow the wheel.

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 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 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 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 It carries air from the foot brake or the trailer hand brake.

Every vehicle equipped with air brakes has two air lines, the service line and the emergency line. The service line (also called the control line or signal line) carries air, which is controlled by the foot brake or the trailer hand brake. The harder you press the foot brake or pull the hand brake, the greater the pressure in the service line.

Not quite. The answer is compressed air enters the brake chambers.

Pressing down on the brake pedal lets air into each brake chamber, forcing the brake pads against the inside of the drum (or the rotor for disc brakes).