Hawaii CDL: Air Brakes Practice Test

Not quite. The answer is 60 psi.

A low pressure warning signal visible to the driver must come on before the pressure in the service air tank falls below 60 psi (or one-half the air compressor governor cutout air pressure on older vehicles).

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 a supply tank.

An Integrated Solution Air Dryer (AD-IS®) and Reservoir System provides an integrated air dryer, purge reservoir, governor, and a number of the charging valve components in a module. The air dryer is so efficient that a supply ("wet") tank is not needed. Instead, the AD-IS sends air directly to the primary and secondary service ("dry") 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 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 3 psi in one minute.

When testing for an air leak, make sure the system is fully charged, turn off the engine, fully apply the foot (service) brake, and hold the brake for one minute. The air pressure should not drop more than 3 psi for a single vehicle or more than 4 psi for a combination vehicle. If it does, check for an air leak somewhere.

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 1 inch

During the walk-around inspection, pull hard on each slack adjuster that you can reach. If it moves more than an inch, it probably needs adjustment.

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 125

The air compressor will start pumping air into the air tanks at about 100 psi and stop at about 125 psi. This action is controlled by the air compressor governor.

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 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 Apply the brakes as hard as you can without locking the wheels.

In controlled braking, you apply the brakes as hard as you can without locking the wheels. Keep steering wheel movements very small while doing this. This method of emergency braking does not require you to lock the wheels. Hence it is compatible with antilock brakes (ABS).

Not quite. The answer is apply the brakes as hard as you can without locking the wheels.

With controlled braking, you brake as hard as you can without locking the wheels, and keep steering to a minimum. If the wheels do lock or you need to steer more than this, release the brakes and reapply them as soon as you can.

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 Hawaii Commercial Driver License Manual does not discuss this topic.)

Source: 49 CFR § 571.121

Not quite. The answer is Ice may form in the air storage tanks and cause the brakes to fail.

Moisture in the warm, compressed air from the air compressor will condense as the air cools. In below-freezing temperatures, this moisture can freeze. Ice in the tanks and air lines can cause the brakes to stop working. Whenever the air compressor runs, the alcohol evaporator puts alcohol vapor into the air brake system to help prevent water in the lines or valves from freezing. (Alcohol has a lower freezing point than water.)

Not quite. The answer is depends on whether the service brakes are in proper adjustment.

The braking power of the spring brakes depends on whether the service brakes are in proper adjustment. If they are not, neither the service brakes nor the emergency/parking brakes will work properly.

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 Under or around the frame

Air from the compressor is stored in air tanks. Located under or around the frame of the vehicle, these tanks are usually made of steel and shaped like cylinders with domed ends.

Not quite. The answer is Between the air compressor and the supply ("wet") tank

The supply ("wet") tank tends to get most of the moisture because moisture condenses there as the hot air from the compressor cools. To help alleviate this situation, the air dryer dries the air from the compressor before it enters the supply tank. Note: Today's air dryer technology is so effective that a "wet" tank may not be needed anymore. In a modern Air Dryer Integrated System (ADIS), air from the air dryer goes directly into the primary and secondary service ("dry") tanks.