Arkansas CDL: Air Brakes Practice Test

Not quite. The answer is Air pressure

Drivers behind you must be warned whenever you brake. The air brake system does this with an electric switch that works by air pressure. The switch turns on the brake lights when you apply the air brakes.

Not quite. The answer is The dashboard air pressure gauges won't drop when it's drained.

It may be difficult to visually identify the supply tank. Instead, remember that your dashboard air pressure gauges monitor the air pressure in the primary and secondary service tanks. (In some vehicles, there are two gauges, one for each service tank; in other vehicles, there is one gauge with two needles.) Draining the service tanks will cause the gauges to show a drop in air pressure in those tanks. The supply tank is the tank that does NOT drop the gauges when it's drained.

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 Stop.

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 Park on level ground. Chock the wheels. Release the parking brake when you have enough air pressure. Shut off the engine. Repeatedly press and release the brake pedal.

To test whether the spring brakes come on, release the parking brake (all vehicles), release the tractor protection valve control (on combination vehicles), and turn off the engine while leaving the electrical power on to power the instrument panel. Then step on and off the brake pedal. The low air pressure warning signal should come on when the pressure has fallen below 55 psi. Continue stepping on and off the brake pedal until you reach about 20–45 psi, at which point the parking brake valve should close or pop out.

Not quite. The answer is the emergency brake system.

The system that uses parts of the service and parking brake systems to stop the vehicle in a brake system failure is called the emergency brake system.

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 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 service

Air brakes are really three braking systems in one: the emergency brake, the parking brake, and the service brake. As these names suggest, when you depress the brake pedal in normal driving, it's the service brake system that applies the brakes.

Not quite. The answer is Between the air compressor and the supply ("wet") tank

The supply ("wet") tank tends to get most of the moisture because moisture condenses there as the hot air from the compressor cools. To help alleviate this situation, the air dryer dries the air from the compressor before it enters the supply tank. Note: Today's air dryer technology is so effective that a "wet" tank may not be needed anymore. In a modern Air Dryer Integrated System (ADIS), air from the air dryer goes directly into the primary and secondary service ("dry") tanks.

Not quite. The answer is With the engine off, step on and off the brake pedal to lower the air pressure below 60 psi.

The best way to test the low air pressure warning signal is to release the parking brake (all vehicles), release the tractor protection valve (on combination vehicles), and turn off the engine of your vehicle while leaving the electrical power on. Then step on and off the brake pedal. The low air pressure warning signal should come on when the pressure falls below 60 psi. You should never need to get down to 30 psi.

Not quite. The answer is With ABS, you do emergency braking differently than without ABS.

Without ABS, hard braking can lock the wheels, resulting in a skid. Therefore, to do emergency braking without ABS, you should use the "stab braking" method or the "controlled braking" method. With ABS, go ahead and brake hard; the ABS computer will prevent your wheels from locking.

Not quite. The answer is whenever you leave the vehicle unattended.

Because air pressure can leak when you're away from your vehicle, it should be set with the parking brake, to keep it from rolling. There is an exception to this rule: if the brakes are too hot or wet, use wheel chocks instead, to avoid brake damage or freezing.

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.

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 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 20 to 45 psi.

An air leak in your brake system can cause your air brakes to fail. If the air pressure drops to the manufacturer's specification (typically 20–45 psi), your spring brakes will come on automatically. You can avoid this by pulling over and checking the air brakes if the low pressure warning light ever comes on.

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 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 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.