New Mexico CDL: Air Brakes Practice Test

Not quite. The answer is depends on whether the service brakes are in proper adjustment.

The braking power of the spring brakes depends on whether the service brakes are in proper adjustment. If they are not, neither the service brakes nor the emergency/parking brakes will work properly.

Not quite. The answer is Radio signal system

The air brakes are made up of three systems: the service brake, the parking brake, and the emergency brake. Before your knowledge test, review the New Mexico Commercial Driver License Manual to familiarize yourself with what each one does.

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 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 reduce air pressure at the front wheels.

Most modern tractors are equipped with an automatic front axle ratio valve, which supersedes the manual front brake limiting valve in older tractors. In light-to-moderate braking, the ratio valve automatically reduces air pressure (and hence braking force) to the front wheels to reduce the chance of front-wheel lockup (which could result in a skid) on slippery roads.

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 Brake firmly while slowly moving forward on level ground.

To test the service brakes, wait to build up normal air pressure. Then move your vehicle forward slowly (at about 5 mph) and brake hard. Check whether your vehicle stops promptly without pulling to one side or the other.

Not quite. The answer is all of the above.

Spring brakes are an important backup system: powerful springs that automatically apply the brakes if they sense that air pressure has been lost for some reason, such as a leak. They will also apply the brakes if the psi gets too low, although ideally, you should take control of your brakes before that happens.

Not quite. The answer is At the end of each working day

Unless your vehicle automatically drains the air tanks, you should drain them at the end of each working day so that the moisture and oil will not freeze or coagulate and cause your brakes to fail.

Not quite. The answer is the brakes when you depress the brake pedal during normal driving.

Air brakes are actually three braking systems in one: the emergency brake, the parking brake, and the service brake. As these terms 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 the braking effect of the engine.

When you drive down long, steep downgrades, the braking effect of your engine is what's most important, and your service 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 Never

Never leave your vehicle unattended without first applying the parking brakes or chocking the wheels. Your vehicle might roll away and hit something – or someone.

Not quite. The answer is to drain moisture and oil out of the tanks.

Water and oil from the compressor can collect at the bottoms of the air tanks. If the air tanks are not drained, the water and oil can freeze or coagulate and cause brake failure.

Not quite. The answer is They are not as strong as service brakes.

Spring brakes start to drag as pressure drops to about 60 psi, and they release as pressure rises to about 60 psi. Yet a full service brake application can be 100 psi. The coil spring in most spring parking brake chambers can exert a force of between 1,500 and 2,000 pounds. With a full service brake application of 100 psi, a typical Type 30 brake chamber can produce a force of 30 × 100 = 3,000 pounds.

Not quite. The answer is glad hands

As part of your vehicle inspection test, if your vehicle is equipped with air brakes and has a trailer, you will inspect the air connections between the truck or tractor and the trailer. These connections are made with hose couplers (commonly called "glad hands" because they vaguely resemble shaking hands). These glad hands have rubber seals to form a tight connection and prevent air from escaping. Make sure that the glad hands are locked in place and free of damage or air leaks.

Not quite. The answer is All vehicles with air brakes currently in operation must have low air pressure warning signals.

All vehicles on the road that have air brakes must have low air pressure warning signals.

Not quite. The answer is Check if the vehicle was manufactured after 1998.

Vehicles manufactured after 1998 are required to have antilock brakes. They also have a yellow ABS malfunction lamp.

Not quite. The answer is All of the above are true.

A dual air brake system is a system designed for safety and used on most heavy-duty vehicles. It uses one set of controls. Typically, the "primary" system operates the regular brakes on the rear axle, and the "secondary" system operates the regular brakes on the front axle.

Not quite. The answer is More than 400 feet

The stopping distance equals the sum of the perception distance, reaction distance, brake lag distance, and braking distance. Under ideal conditions, the average driver of a bus or large truck equipped with air brakes and traveling at 55 mph would require about 451 feet to come to a complete stop. The length of a football field including the two end zones is 360 feet.

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).