Nevada CDL: Air Brakes Practice Test

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 Use gloves and pull hard on each slack adjuster you can reach.

To check the slack adjusters, try to pull on them manually while wearing gloves. If there is an inch or more of "give," there is an issue and they should be fixed.

Not quite. The answer is 35 mph.

On a steep downgrade, continuous application of the service brakes 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. (In this case, with a "safe" speed of 40 mph, you should brake gently until your speed drops to 35 mph.) 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 brake drum.

In North America, the most common type of foundation brake is the S-cam drum brake. The brake shoes and linings press against the inside of the brake drum, which causes friction to slow the wheel.

Not quite. The answer is 100 psi.

In a typical air brake system, pumping by the air compressor should start at about 100 psi and stop at about 125 psi. (Check the manufacturer's specifications for the actual figures.)

Not quite. The answer is takes longer than hydraulic fluid to flow through the lines.

With hydraulic brakes, hydraulic fluid is always in the system, so the brakes will be applied instantly when you depress the brake pedal. With air brakes, the compressed air must flow through a complex series of lines, valves, etc., to reach and fill the brake chambers before the brakes can begin to slow your vehicle. This "brake lag" can take at least a half second.

Not quite. The answer is air pressure.

Spring brakes contain powerful springs that are normally held back by air pressure. If the pressure drops too low, the spring brakes will automatically kick in.

Not quite. The answer is 2 psi per minute.

Perform the first test of air leakage with the engine off and the brakes released. The air-loss rate should be less than 3 psi per minute for a combination vehicle and less than 2 psi per minute for a bus or straight truck. After you've tested this initial drop, now test air leakage with the engine off and the foot brake fully applied. This time, the air-loss rate should be less than 4 psi per minute for a combination vehicle and less than 3 psi per minute for a bus or straight truck.

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 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 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 when air is pumped into the air storage tanks.

The air compressor runs at all times while the engine is running. To keep the air pressure from eventually rising too high, the air compressor governor controls when the compressed air from the air compressor should flow into the air reservoirs. When air pressure drops to a certain level (typically 100 psi), the governor "cuts in" and routes the compressed air into the storage tanks. When air pressure rises to a certain level (typically 125 psi), the governor "cuts out" and routes the compressed air out of the system, into the atmosphere.

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 park on level ground, chock the wheels, and release the parking brakes.

Chock the wheels so you can release the parking brakes safely. Then put on gloves and pull hard on each slack adjuster you can reach. If it moves more than about one inch, it needs to be adjusted.

Not quite. The answer is They work as a supplement to the braking effect of your engine.

When you drive down long, steep downgrades, the braking effect of your engine is what's most important, and your brakes are only a supplement to being in the proper low gear. They cannot compensate for your vehicle being in an unsafe high gear without putting too much pressure on your brakes.

Not quite. The answer is In the first tank to which the air compressor pumps air

A safety relief valve is installed in the first tank that the air compressor pumps air to. This tank is known as the supply or "wet" tank. The safety valve protects the tank and the rest of the system from too much pressure. The valve is usually set to open at 150 psi.

Not quite. The answer is Clockwise until the bolt stops turning

Adjusting an automatic slack adjuster is an emergency procedure that you should perform only if your brakes have failed on the road. Most automatic slack adjusters have a hexagonal (six-sided) adjusting bolt. For this type of slack adjuster, first turn the bolt clockwise until it stops turning. If the slack adjuster has a square adjusting bolt, first turn the bolt counterclockwise until it stops turning. Then with either type of bolt, back it off about half a turn in the opposite direction.

Not quite. The answer is They are springs that apply the brakes if air pressure drops too low.

Spring brakes are an important backup system: powerful springs that automatically apply the brakes if they sense that air pressure has dropped too low for effective braking. The spring brakes are also used as parking brakes.

Not quite. The answer is Tap on the brake drums.

If a brake lining has gotten frozen to the brake drum, you should be able to free it by using a hammer to tap on the drum near the brake lining. Be careful not to hit the brake lining because you might damage it. Note that you may also need to free the other brake lining in that drum brake. If the valves or other parts of the air braking system are frozen, you may be able to get them unstuck by putting commercial air brake antifreeze (NOT pure methyl alcohol) into the trailer air supply (red) line. However, this will not free frozen brake linings.