Air Brake Test Basic 3 — Questions and Answers
Question 1: What holds a spring brake in the released position during normal driving?
- Air pressure (Correct answer)
- The slack adjuster
- Engine vacuum
- The governor
Correct answer: Air pressure
Air pressure compresses the power spring to keep spring brakes released.
Question 2: What happens to spring brakes if system air pressure drops too low?
- They automatically apply (Correct answer)
- They release completely
- They disable steering
- They speed up the vehicle
Correct answer: They automatically apply
Spring brakes apply automatically when air pressure falls too low.
Question 3: How should you test the service brakes during a pre-trip air brake check?
- Roll forward slowly and apply the brake pedal firmly (Correct answer)
- Pump the pedal 20 times while parked
- Rev the engine to build pressure
- Disconnect the trailer line
Correct answer: Roll forward slowly and apply the brake pedal firmly
Move forward at low speed and apply the brakes to confirm they stop the vehicle and do not pull.
Question 4: What is brake fade in an air brake system?
- Loss of braking power from overheated brakes (Correct answer)
- A drop in air pressure overnight
- A cracked brake chamber
- A frozen air line
Correct answer: Loss of braking power from overheated brakes
Brake fade is reduced stopping power caused by excessive heat from prolonged braking.
Question 5: What is the proper braking technique on a long, steep downgrade?
- Use a low gear and light, steady brake application (Correct answer)
- Ride the brakes continuously
- Shift to neutral and coast
- Pump the brakes rapidly the whole way
Correct answer: Use a low gear and light, steady brake application
Select a low gear for engine braking and use steady, controlled brake applications.
Question 6: What does the air pressure gauge in the cab show the driver?
- The amount of pressure in the air tanks (Correct answer)
- The speed of the compressor
- The temperature of the brakes
- The weight of the load
Correct answer: The amount of pressure in the air tanks
The gauge displays the air pressure available in the reservoir tanks.
Question 7: Why do air brakes have a slight time lag compared to hydraulic brakes?
- Air must travel through the lines before brakes apply (Correct answer)
- The pedal is heavier
- The driver must pump twice
- The compressor must restart each time
Correct answer: Air must travel through the lines before brakes apply
It takes a brief moment for air to move through the lines and apply the brakes.
Air Brake Test Basic 3
What holds a spring brake in the released position during normal driving?