Idaho CDL: Air Brakes Practice Test

Not quite. The answer is the service brake valve and the parking brake valve.

A spring parking brake can exert a force of up to 2,000 pounds, and a Type 30 service brake chamber can exert a force of 3,000 pounds or more. If both forces were applied at the same time (which is called compounding the service and parking brakes), the combined force could damage parts of the braking system. To prevent this, most modern commercial vehicles employ an anti-compounding valve. One input port of this valve is connected to the service brake valve (foot valve), and another input port is connected to the parking brake valve (yellow knob). Suppose you set the parking brakes by pulling out the yellow knob. That valve will send air to the anti-compounding valve. If you also press the brake pedal, the foot valve will also send air to the anti-compounding valve. Then the anti-compounding valve will partially release the parking brakes by the same amount of force that the foot valve has applied.

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).

Not quite. The answer is You will still have normal brake function and will just need to get the ABS repaired soon.

Losing the ABS function does not change the basic parts of your truck, so you will still have the same brakes that you have always had. Simply use them and get the ABS repaired as soon as possible. There is no need to panic, unless your system shows other and more serious warnings.

Not quite. The answer is The vehicle was manufactured after 1998.

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

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

Oil and water can start to collect in the bottom of an air tank and can cause brake failure if it's not drained. 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 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 All vehicles with air brakes currently in operation

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

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 If the brakes are very hot

If the brakes are too hot, avoid using the parking brakes because the heat may warp and damage the brakes. Also avoid using the parking brakes if they are wet and at risk of freezing. If the parking brakes freeze, your vehicle will be immobilized. In both of these situations, use wheel chocks instead.

Not quite. The answer is a supply pressure gauge.

Every vehicle equipped with air brakes must have a supply pressure gauge that shows how much air pressure is available for braking.

Not quite. The answer is that you are applying to the brakes.

If your vehicle is so equipped, the application pressure gauge will show how much air pressure you are applying to the brakes. If you have to apply more pressure than before to achieve the same braking effect, your brakes are fading (becoming less effective).

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 55 to 60 psi.

A low pressure warning signal visible to the driver must come on before the pressure in the service air tank falls below 55 psi (or one-half the air compressor governor cutout air pressure on older vehicles).

Not quite. The answer is release the spring brakes.

Even after loss of air pressure has caused the spring brakes to come on, you may need to move the vehicle again in an emergency. Some vehicles such as buses have a separate air tank that can be used to release the spring brakes. You can then move the vehicle, after which you can set the spring brakes again. This action is controlled by dual parking control valves: One valve lets air flow from this air tank to release the spring brakes, and the other valve sets them again.

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 3 psi in one minute.

When testing for an air leak, make sure the system is fully charged, turn off the engine, fully apply the foot (service) brake, and hold the brake for one minute. The air pressure should not drop more than 3 psi for a single vehicle or more than 4 psi for a combination vehicle. If it does, check for an air leak somewhere.

Not quite. The answer is let the air out of the brake chambers.

The parking brake control allows you to evacuate air from the brake chambers. With the air gone, the spring brakes will come on automatically and hold your vehicle in place.

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 1/4 inch

According to federal regulations on air brakes, the brake linings of non-steering-axle brakes must be at least 1/8 inch thick for disc brakes or at least 1/4 inch thick for drum brakes. The brake linings of steering-axle drum brakes can be thinner.

Not quite. The answer is turn off the engine, release the parking brake, and let the system settle.

To test for an air leak, turn off the engine, release the parking brake (i.e., push the parking brake control knob in), and see how fast the air pressure drops. The air pressure should drop less than 2 psi in one minute for a single vehicle and less than 3 psi for a combination vehicle.