North Carolina CDL: Air Brakes Practice Test

Not quite. The answer is that you are applying to the brakes.

If your vehicle is so equipped, the application pressure gauge will show how much air pressure you are applying to the brakes. If you have to apply more pressure than before to achieve the same braking effect, your brakes are fading (becoming less effective).

Not quite. The answer is the brake shoes.

In an S-cam drum brake, the brake spider serves as the main mounting base for the brake shoes. One end of each brake shoe is connected to the brake spider with an anchor pin. The anchor pin allows the brake shoe to pivot as the brake shoes are applied to the brake drum.

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 Safety valve

Drum brakes are on each of your vehicle's axles and contain about 10 different parts, including the axle, slack adjuster, and brake drum itself. While a safety valve is part of the air brake system, it is not part of the drum brake.

Not quite. The answer is brake in a straight line.

In controlled braking, you brake as hard as you can without locking the wheels. As you do this, keep your vehicle going relatively straight.

Not quite. The answer is They help maintain correct pushrod stroke.

An automatic slack adjuster automatically compensates for normal brake lining wear by adjusting pushrod stroke. Automatic slack adjusters should not normally require manual adjustment of pushrod stroke. However, they still require lubrication at regular intervals.

Not quite. The answer is yellow

If your vehicle has ABS, there will be a yellow ABS malfunction lamp on the instrument panel. When you start the engine, the ABS malfunction lamp will come on momentarily to show that the lamp works. But if the lamp comes on and stays on, it means there is a problem with the ABS.

Not quite. The answer is Before driving

Air compressors are either belt driven or (as is more often the case these days) gear driven directly from the engine. Most modern compressors are cooled by the engine cooling system and are lubricated by engine oil. However, some compressors may still be self lubricated or air cooled. If the compressor has its own oil supply, check the oil level before you drive.

Not quite. The answer is hazardous in direct exposure.

The compressed air that is used in air brake systems can be hazardous if you get near it when it is being exhausted from the vehicle. Compressed air leaving the vehicle travels at a very high speed and carries moisture, oil, dirt, and dust. To avoid exposing yourself to it, learn about all the places where the compressed air can be exhausted from your vehicle (such as the exhaust ports of brake valves).

Not quite. The answer is parts of the service brakes and parking brakes

Spring brakes use powerful springs to apply the brakes. Normally, air pressure in the brake chambers holds back the springs. Should air pressure drop too low because of a leak, the springs will apply the brakes and stop the vehicle. To apply the parking brakes, you release air from the brake chambers manually.

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 Stop.

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 the service brake valve and the parking brake valve.

A spring parking brake can exert a force of up to 2,000 pounds, and a Type 30 service brake chamber can exert a force of 3,000 pounds or more. If both forces were applied at the same time (which is called compounding the service and parking brakes), the combined force could damage parts of the braking system. To prevent this, most modern commercial vehicles employ an anti-compounding valve. One input port of this valve is connected to the service brake valve (foot valve), and another input port is connected to the parking brake valve (yellow knob). Suppose you set the parking brakes by pulling out the yellow knob. That valve will send air to the anti-compounding valve. If you also press the brake pedal, the foot valve will also send air to the anti-compounding valve. Then the anti-compounding valve will partially release the parking brakes by the same amount of force that the foot valve has applied.

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 Do all of the above.

To ensure that your vehicle will be safe when you leave it unattended, apply the parking brakes and chock the wheels. Removing the keys is a simple safety tip for any vehicle, even a passenger car.

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 In the first tank to which the air compressor pumps air

A safety relief valve is installed in the first tank that the air compressor pumps air to. This tank is known as the supply or "wet" tank. The safety valve protects the tank and the rest of the system from too much pressure. The valve is usually set to open at 150 psi.

Not quite. The answer is To show how much pressure is in the air tanks.

The air supply pressure gauge is connected to the air tank (or possibly to both tanks in a dual air tank system). It shows how much air pressure is in the air tanks.

Not quite. The answer is 20 to 45 psi.

An air leak in your brake system can cause your air brakes to fail. If the air pressure drops to the manufacturer's specification (typically 20–45 psi), your spring brakes will come on automatically. You can avoid this by pulling over and checking the air brakes if the low pressure warning light ever comes on.

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.