CDL air brakes practice test

A: Service brake, parking brake, and emergency brake. The manual describes air brakes as three systems: the service brake for normal stops, the parking brake, and the emergency brake that stops the vehicle if the system fails. Commercial Driver's License Manual (CDL Driver's Manual): Section 5 Air Brakes (introduction), page 5-1.

C: It uses parts of the service and parking brake systems to stop the vehicle if the brake system fails. There is no separate set of emergency brakes: when the brake system fails, the emergency system borrows parts of the service and parking brake systems to bring the vehicle to a stop. Commercial Driver's License Manual (CDL Driver's Manual): Section 5 Air Brakes (introduction), page 5-1.

B: Water and compressor oil collect in them and can cause brake failure. Compressed air contains water and oil that collect at the bottom of the tanks; water can freeze in cold weather and cause the brakes to fail. Commercial Driver's License Manual (CDL Driver's Manual): 5.1.4 Air Tank Drains, page 5-1.

C: A yellow, diamond-shaped push-pull knob. Newer vehicles use a yellow, diamond-shaped push-pull knob to control the parking (spring) brakes. Commercial Driver's License Manual (CDL Driver's Manual): 5.1.15 Parking Brake Controls, page 5-3.

A: The time it takes for the brakes to work after you push the pedal, while air flows through the lines. Brake lag is the time the brakes need to work after the pedal is pushed, because air has to flow through the lines to the brakes. Commercial Driver's License Manual (CDL Driver's Manual): 5.4.4 Stopping Distance, page 5-8.

B: The service brake system. The service brake system is the one you work with the brake pedal during normal driving. Commercial Driver's License Manual (CDL Driver's Manual): Section 5 Air Brakes (introduction), page 5-1.

A: Enough air to use the brakes several times. The tanks hold enough compressed air to let you use the brakes several times even if the compressor stops working. Commercial Driver's License Manual (CDL Driver's Manual): 5.1.3 Air Storage Tanks, page 5-1.

D: To help keep the automatic drain from freezing in cold weather. Heating devices on automatic drains help prevent the drain from freezing in cold weather. Commercial Driver's License Manual (CDL Driver's Manual): 5.1.4 Air Tank Drains, page 5-1.

A: Pull the knob out. Pull the knob out to put the parking (spring) brakes on, and push it in to release them. Commercial Driver's License Manual (CDL Driver's Manual): 5.1.15 Parking Brake Controls, page 5-3.

B: One half second or more. Hydraulic brakes respond right away, but air has to travel through the lines first, which adds a delay of half a second or more. Commercial Driver's License Manual (CDL Driver's Manual): 5.4.4 Stopping Distance, page 5-8.

C: Pumps air into the air storage tanks (reservoirs). The air compressor's job is to pump air into the air storage tanks. Commercial Driver's License Manual (CDL Driver's Manual): 5.1.1 Air Compressor, page 5-1.

C: The brakes won't work. The manual warns that if pressure gets too low, the brakes won't work. Commercial Driver's License Manual (CDL Driver's Manual): 5.1.7 The Brake Pedal, page 5-2.

D: Puts alcohol into the air system to reduce the risk of ice in valves and other parts. An alcohol evaporator adds alcohol to the air to cut the risk of ice forming in brake valves and other parts in cold weather. Commercial Driver's License Manual (CDL Driver's Manual): 5.1.5 Alcohol Evaporator, page 5-2.

D: The combined forces of the springs and air pressure could damage the brakes. Pushing the pedal while the spring brakes are on can damage the brakes through the combined force of the springs and air pressure. Not all systems prevent this, so make it a habit not to do it. Commercial Driver's License Manual (CDL Driver's Manual): 5.1.15 Parking Brake Controls, page 5-3.

A: Perception distance + reaction distance + brake lag distance + braking distance. With air brakes, total stopping distance = perception distance + reaction distance + brake lag distance + braking distance. Commercial Driver's License Manual (CDL Driver's Manual): 5.4.4 Stopping Distance, page 5-8.

D: Through gears or a V-belt. The compressor is driven by the engine, either by gears or by a V-belt. Commercial Driver's License Manual (CDL Driver's Manual): 5.1.1 Air Compressor, page 5-1.

B: 20 to 45 psi (typically 20 to 30 psi). The manual says tractor and straight truck spring brakes come fully on when pressure drops to 20-45 psi, typically 20-30 psi. Commercial Driver's License Manual (CDL Driver's Manual): 5.1.14 Spring Brakes, page 5-3.

A: Daily air tank draining, plus checking and filling the alcohol container every day. In cold weather, check and top up the alcohol container every day. The evaporator does not remove water and oil, so tanks without automatic drains still need draining daily. Commercial Driver's License Manual (CDL Driver's Manual): 5.1.5 Alcohol Evaporator, page 5-2.

C: Move it as far as it will go and hold it there with the locking device. To park with a modulating valve, push the lever to the end of its travel and secure it with the locking device. Commercial Driver's License Manual (CDL Driver's Manual): 5.1.15 Parking Brake Controls, page 5-3.

B: About 32 feet. The manual says air brake lag at 55 mph on dry pavement adds about 32 feet. Commercial Driver's License Manual (CDL Driver's Manual): 5.4.4 Stopping Distance, page 5-8.

D: Check the oil level before driving. A compressor may be lubricated by engine oil or have its own oil supply; if it has its own supply, check that oil level before you drive. Commercial Driver's License Manual (CDL Driver's Manual): 5.1.1 Air Compressor, page 5-1.

B: Bring the vehicle to a safe stop right away, while you can still control the brakes. Don't wait for the spring brakes to come on by themselves. When the warning first comes on, stop safely right away while you can still control the brakes. Commercial Driver's License Manual (CDL Driver's Manual): 5.1.14 Spring Brakes, page 5-3.

B: How hard and how long the brakes are used. A drum's tolerance for heat depends on how hard the brakes are applied and for how long. Too much heat can cause the brakes to stop working. Commercial Driver's License Manual (CDL Driver's Manual): 5.1.8 Foundation Brakes, page 5-2.

C: Stop, put the parking brake on, and gently pull against it in a low gear. Stop the vehicle, set the parking brake, and gently pull against it in a low gear to make sure it holds. Commercial Driver's License Manual (CDL Driver's Manual): 5.3.3 Step 7 Final Air Brake Check, page 5-7.

C: Over 450 feet. At 55 mph under good traction and brake conditions, total stopping distance for an air-braked vehicle is over 450 feet. Commercial Driver's License Manual (CDL Driver's Manual): 5.4.4 Stopping Distance, page 5-8.