Ohio CDL: Air Brakes Practice Test

Not quite. The answer is expansion of the brake drums.

Overusing the service brakes can cause overheating and expansion of the brake drums. The brake shoes will have to move farther to contact the brake drums, making braking harder or eventually impossible (brake fade).

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 lets the air out of the brake chambers.

When you apply the parking brake control, air is released from the brake chambers, causing the springs to apply the brakes and hold your vehicle in place.

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.

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 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 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 all of the above.

Slack adjusters are an important part of your air brake system that allows you to adjust the brakes to ensure that they are safe. They are located in different places, depending on the type of brakes that you have.

Not quite. The answer is spring pressure.

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

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 your brakes may fail because of water freezing.

Your air tanks hold a mixture of water and compressor oil. If left inside to collect at the bottom, the water may freeze and cause brake failure.

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 the brakes to fade.

Excessive heat caused by overuse of the brakes can expand the brake drums away from the brake pads or shoes and affect the brake linings, reducing friction. The brakes will fade (lose their effectiveness). On a long or steep downgrade, rely on engine braking more than the service brakes.

Not quite. The answer is Never

It used to be thought that applying the steering axle brakes on a slippery surface might cause a front-wheel skid. However, more recent tests have shown that front-wheel braking is good under all driving conditions. Front-wheel skids from braking are unlikely even on ice. Therefore, always have front-wheel braking available. If you're driving an old truck equipped with a front brake limiting valve, leave the control set at "normal" to have normal stopping power. The front-wheel brakes provide about 12% of the total stopping power of a loaded combination vehicle.

Not quite. The answer is one-half

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

Not quite. The answer is Stop and park safely.

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 All weather conditions

Front wheel brakes have been shown to be ideal under all weather and driving conditions. Front wheel braking is unlikely to cause a skid even on icy roads.

Not quite. The answer is brake normally.

Antilock brakes will automatically keep your wheels from locking so you can brake normally.

Not quite. The answer is Whenever your vehicle is parked

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 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.