Florida CDL: Air Brakes Practice Test

Not quite. The answer is the brake shoes.

In an S-cam drum brake, the brake spider serves as the main mounting base for the brake shoes. One end of each brake shoe is connected to the brake spider with an anchor pin. The anchor pin allows the brake shoe to pivot as the brake shoes are applied to the brake drum.

Not quite. The answer is turns on the brake lights when you brake.

The stop light switch is an electric switch triggered by air pressure. When you apply the service brakes, the stop light switch turns on the brake lights.

Not quite. The answer is 10

A CMV has two foundation brakes per axle (one on each side). A typical 18-wheeler has five axles: the steering axle, the two tandem drive axles, and the two tandem semi-trailer axles. Therefore, there are 5 × 2 = 10 foundation brakes on the vehicle. Note: According to FMCSA, even a lift axle must have brakes when it is in contact with the roadway.

Not quite. The answer is It disables the spring brake.

If your vehicle's service brakes fail, the emergency (spring) brakes will activate and stop your vehicle. Then to tow your vehicle for repairs, it will be necessary to disable the spring brakes. A technician can manually compress or "cage" the spring in each spring brake chamber. Obviously, the vehicle will be undrivable at this point because it will have no working brakes at all.

Not quite. The answer is It supplies compressed air from the service tank with the highest pressure.

A two-way check valve allows compressed air from two different sources to flow through the same air line. The valve will select the source with the higher pressure. In this case, a two-way check valve is connected to both the primary and secondary service tanks to always draw air from the tank with the higher pressure and send it to the parking brake control valve. This arrangement ensures that the higher pressure is available to release the spring parking brakes. It also ensures that the spring parking brakes will not activate if pressure is lost in just one of the two tanks.

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.

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 Never

It used to be thought that applying the steering axle brakes on a slippery surface might cause a front-wheel skid. However, more recent tests have shown that front-wheel braking is good under all driving conditions. Front-wheel skids from braking are unlikely even on ice. Therefore, always have front-wheel braking available. If you're driving an old truck equipped with a front brake limiting valve, leave the control set at "normal" to have normal stopping power. The front-wheel brakes provide about 12% of the total stopping power of a loaded combination vehicle.

Not quite. The answer is press the brake pedal as hard as you can, release the brakes when the wheels lock, and apply the brakes again when the wheels start to roll.

To stop with stab braking, brake hard, release the brakes once the wheels lock, and then brake hard once the wheels start to roll again. (Note that this method won't work if your vehicle has antilock brakes, because the wheels won't lock. Use controlled braking instead.)

Not quite. The answer is controls the air pressure applied to the service brakes.

The brake pedal controls the amount of air pressure applied to the service brakes. The harder the pedal is pushed, the more air pressure is applied to the brakes.

Not quite. The answer is Ice may form in the air storage tanks and cause the brakes to fail.

Moisture in the warm, compressed air from the air compressor will condense as the air cools. In below-freezing temperatures, this moisture can freeze. Ice in the tanks and air lines can cause the brakes to stop working. Whenever the air compressor runs, the alcohol evaporator puts alcohol vapor into the air brake system to help prevent water in the lines or valves from freezing. (Alcohol has a lower freezing point than water.)

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 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 Never

Never try to apply the brake pedal when the spring brakes are on. The combined force of the springs and the air pressure could damage the brakes. However, the brake systems on some (but not all) vehicles are designed to prevent this from happening.

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 to tell you how much air is in the tank.

The supply pressure gauge tells you how much air is in the tank at all times. In some vehicles, it may be connected to a warning bell or light.

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 2 psi per minute.

To test the static air leakage rate, 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 in one minute for a combination vehicle.

Not quite. The answer is a Class A CDL without an air brakes restriction.

To legally pull a trailer whose gross vehicle weight rating (GCWR) exceeds 10,000 pounds, you'll have to obtain a Class A CDL. If you don't pass a knowledge test on air brakes, your CDL will include a restriction limiting you to driving only vehicles without air brakes.

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.