New Jersey CDL: Air Brakes Practice Test

Not quite. The answer is does all of the above.

The tractor protection valve protects your air brake system by providing the air supply, closing automatically if the air supply drops too low, and closing if you apply the parking brakes.

Not quite. The answer is check the alcohol level

Alcohol vapor from the alcohol evaporator helps keep ice from forming in the lines and valves of the air brake system. Check the alcohol level daily and refill as needed.

Not quite. The answer is activates when your wheels are about to lock up.

ABS does not have much effect on your everyday driving. It does not affect your braking capability or necessarily shorten your stopping distance. It just helps you keep control of your vehicle by activating when your wheels are about to lock up.

Not quite. The answer is It disables the spring brake.

If your vehicle's service brakes fail, the emergency (spring) brakes will activate and stop your vehicle. Then to tow your vehicle for repairs, it will be necessary to disable the spring brakes. A technician can manually compress or "cage" the spring in each spring brake chamber. Obviously, the vehicle will be undrivable at this point because it will have no working brakes at all.

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 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 a supply pressure gauge.

A supply pressure gauge is connected to a service tank (or possibly to both service tanks in a dual air brake system). It shows the amount of air pressure in the service tank.

Not quite. The answer is forces the brake shoes against the inside of the brake drum.

When the S-cam rotates, it forces the brake shoes apart and against the inside of the brake drum. Friction will slow the rotation of the wheel.

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 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 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 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 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 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 10

A CMV has two foundation brakes per axle (one on each side). A typical 18-wheeler has five axles: the steering axle, the two tandem drive axles, and the two tandem semi-trailer axles. Therefore, there are 5 × 2 = 10 foundation brakes on the vehicle. Note: According to FMCSA, even a lift axle must have brakes when it is in contact with the roadway.

Not quite. The answer is 2 psi per minute.

To test the static air leakage rate, turn off the engine, release the parking brake (i.e., push the parking brake control knob in), and see how fast the air pressure drops. The air pressure should drop less than 2 psi in one minute for a single vehicle and less than 3 psi in one minute for a combination vehicle.

Not quite. The answer is It depends on the adjustment of the service brakes.

The braking power of spring brakes depends on the brakes being in adjustment. If the brakes are not adjusted properly, neither the service brakes nor the emergency or parking brakes will work right.

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 Yes, but only if the alcohol evaporator is located downstream from the air dryer.

The air dryer contains a desiccant pack. A desiccant is a chemical agent designed to remove moisture. However, alcohol vapor from the alcohol evaporator (injector) can damage the desiccant. Hence, if an alcohol evaporator is installed, it must be located downstream from the air dryer.

Not quite. The answer is compressed air

Air brakes use compressed air to make the brakes work.