Utah CDL: Air Brakes Practice Test

Not quite. The answer is spring pressure.

Federal safety regulations require buses and trucks to have parking and emergency brakes that don't work on compressed air or hydraulic fluid (because these can leak away). Hence, the parking and emergency brakes rely on mechanical force, such as springs.

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 Never

Never try to apply the brake pedal when the spring brakes are on. The combined force of the springs and the air pressure could damage the brakes. However, the brake systems on some (but not all) vehicles are designed to prevent this from happening.

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 Pressure-protection valve

Various auxiliary air systems, such as air suspension and the driver and passenger air seats, usually get their air from the service tanks of the air braking system. To prevent the tanks from losing air in the event of a leak or failure in an auxiliary air system, a pressure-protection valve is installed between each auxiliary air system and the service tank. If tank pressure drops below a preset level, the pressure-protection valve will close to stop any more air from flowing to the auxiliary air system.

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 always keep it on the "normal" setting.

Some older vehicles have a manually controlled front brake limiting valve to reduce air pressure to the front brakes when traveling on slippery roads. However, tests have since shown that front wheel braking is unlikely to cause a skid even on slippery roads. And reducing the air pressure reduces the vehicle's stopping power. Keep the front brake limiting valve on the "normal" setting at all times.

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.

Not quite. The answer is so you only have to apply the brakes just hard enough to feel a definite slowdown.

When starting down a downgrade, shift into a low gear and use engine braking to slow your vehicle. Apply the brakes just enough to keep your vehicle near your safe speed.

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 brake firmly while slowly moving forward.

To test the service brakes, wait for normal air pressure. Then move your vehicle forward slowly (at about 5 mph) and brake hard. Check whether your vehicle stops promptly without pulling to one side or the other.

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 (b) or (c)

Before measuring pushrod stroke, chock the wheels of your vehicle. For an accurate measurement, make sure that tank air pressures are 90–100 psi. Here are two different methods for measuring pushrod stroke: (1) Make a mark on the pushrod where it exits the brake chamber, and see how far it moves from the brake chamber when the service brakes are applied. (2) Measure the length of the part of the pushrod from the brake chamber to the center of the clevis pin, and see how much it increases when the brakes are applied. To perform either method efficiently, two people may be needed: one to apply the service brakes, and one to make the appropriate measurements before and after the brakes are applied. There are also various pushrod stroke measuring tools available commercially that you can use.

Not quite. The answer is you will still have enough air in the storage tanks to apply the air brakes several times.

The air storage tanks hold enough air for you to apply the air brakes several times.

Not quite. The answer is You should drive faster so that you will be able to keep the trailer and tractor straight.

When driving a tractor-trailer combination vehicle that has ABS, drive the same way that you always have. Do not drive any differently just because of ABS. Only use the braking necessary to keep control, pay attention when you slow down, and brake the same way regardless of what you're driving. Never speed up unless it is part of the safe driving process already.

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 They are not as strong as service brakes.

Spring brakes start to drag as pressure drops to about 60 psi, and they release as pressure rises to about 60 psi. Yet a full service brake application can be 100 psi. The coil spring in most spring parking brake chambers can exert a force of between 1,500 and 2,000 pounds. With a full service brake application of 100 psi, a typical Type 30 brake chamber can produce a force of 30 × 100 = 3,000 pounds.

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 one-half

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

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.