CDL Air Brake - Commercial Driver's License Air Brakes Using Service and Emergency Brakes Questions and Answers

Question 1

When making an emergency stop with a vehicle that has air brakes, what is the 'stab braking' method?

Accepted Answer

Applying the brakes fully until the wheels lock, then releasing them until the wheels start rolling and reapplying.

Answer

Applying the brakes as hard as possible without locking the wheels.

Answer

Pumping the brake pedal quickly and lightly to prevent overheating.

Answer

Alternately applying the service brake and the parking brake to bring the vehicle to a stop.

Question 2

You are driving a vehicle with a dual air brake system. The low air pressure warning light and buzzer come on. What is the safest course of action?

Accepted Answer

Stop and safely park the vehicle as soon as possible.

Answer

Continue driving to the nearest service station while monitoring the gauges.

Answer

Downshift and use the engine brake to slow down, preserving the remaining air pressure.

Answer

Increase your following distance and avoid using the brakes unless absolutely necessary.

Question 3

What is 'brake lag' in a vehicle with air brakes?

Accepted Answer

The time it takes for the air to flow through the lines and apply the brakes after the pedal is pushed.

Answer

The distance the vehicle travels after the driver decides to brake but before they physically apply the pedal.

Answer

The fading of brakes due to excessive heat from overuse on a downgrade.

Answer

The delay caused by wet brake linings, which reduces braking efficiency.

Question 4

A driver is descending a long, steep grade. Which of the following is the correct method for using the service brakes?

Accepted Answer

When speed increases to the 'safe speed', apply the brakes firmly to reduce speed to approximately 5 mph below the safe speed, then release.

Answer

Apply light, steady pressure on the brake pedal all the way down the grade.

Answer

Pump the brakes on and off every few seconds to keep them cool.

Answer

Use the hand-operated trailer brake exclusively to save the tractor's service brakes.

Question 5

The emergency brake system in a vehicle with air brakes uses parts of which two other systems?

Accepted Answer

The service brake and the parking brake systems.

Answer

The service brake and the engine retarder systems.

Answer

The parking brake and the hydraulic brake systems.

Answer

The anti-lock brake and the traction control systems.

Question 6

During a pre-trip inspection, you notice that the spring brakes do not automatically apply when the air pressure drops to the 20-45 PSI range. This indicates a problem with the:

Accepted Answer

Parking brake control valve.

Answer

Air compressor governor.

Answer

Brake drum temperature.

Answer

Service brake pedal.