Wyoming CDL: Air Brakes Practice Test

Not quite. The answer is turn off the engine, release the parking brake, and let the system settle.

To test for an air leak, 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 for a combination vehicle.

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 either (a) or (b).

If you need to stop quickly, use either the "controlled braking" method or the "stab braking" method. However, if your vehicle has antilock brakes, stab braking won't work because the wheels won't lock. Use controlled braking instead.

Not quite. The answer is at all wheels.

Foundation brakes are found at each wheel. The most common type of foundation brake is the S-cam drum brake.

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 your brakes may fail because of water freezing.

Oil and water can start to collect at the bottom of an air tank, which can lead to brake failure. Unless your vehicle automatically drains the air tanks, you should drain them at the end of each working day so the moisture and oil will not freeze or coagulate and cause your brakes to fail.

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 S-cam drum brake.

Foundation brakes are present on each wheel. In North America as of this writing, S-cam drum brakes are much more common than wedge or disc brakes.

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 Every time you leave your vehicle, with a few exceptions

You should always use your parking brake except when the brakes are very hot or they are wet and at risk of freezing.

Not quite. The answer is Don't lock the wheels for longer than an instant.

When braking hard, don't lock the wheels for longer than an instant (which is done in stab braking). If the wheels stay locked, they will lose the grip of the road and your vehicle may skid or even jackknife.

Not quite. The answer is Overheating, low air pressure, and not relying on the engine braking effect

Brake fade and failure are usually due to incorrect use of the brakes that causes overheating. 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. Air brakes will also fail if air pressure drops too low.

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 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 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 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 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).

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 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 controls the air pressure to operate the brakes.

When you press the brake pedal in a CMV equipped with air brakes, the foot valve underneath the pedal opens to allow compressed air to flow to the brake chambers. The brake chambers exert mechanical force to operate the foundation brakes.