ELDT Vehicle Systems and Malfunctions 3 — Questions and Answers
Question 1: What is the purpose of the spring brakes (parking brakes) in an air brake system?
- To provide extra stopping power at high speed
- To hold the vehicle in place using spring force when air is released (Correct answer)
- To cool the brake drums
- To power the trailer lights
Correct answer: To hold the vehicle in place using spring force when air is released
Spring brakes apply by spring force when air pressure is released, holding the vehicle.
Question 2: During the air brake test, how much air pressure loss per minute is acceptable for a single vehicle with the engine off and brakes released?
- No more than 1 psi
- No more than 2 psi (Correct answer)
- No more than 3 psi
- No more than 5 psi
Correct answer: No more than 2 psi
A single vehicle should not lose more than 2 psi per minute with brakes released.
Question 3: A driver notices the tractor's alternator gauge showing no charge while driving. What is the likely consequence if ignored?
- Tire blowout
- Battery drains and electrical systems fail (Correct answer)
- Brakes lock up
- Engine overheats instantly
Correct answer: Battery drains and electrical systems fail
A failed charging system drains the battery, eventually killing electrical and lighting systems.
Question 4: What should you check to detect a slack adjuster problem on air brakes?
- Excessive free travel when the push rod is pulled by hand (Correct answer)
- The color of the brake fluid
- The tread depth of the tires
- The tension of the fan belt
Correct answer: Excessive free travel when the push rod is pulled by hand
Excessive push-rod travel indicates brakes out of adjustment at the slack adjuster.
Question 5: A hissing sound of escaping air after you release the brake pedal most likely indicates what?
- Normal operation
- An air leak in the brake system (Correct answer)
- A worn tire
- Low engine oil
Correct answer: An air leak in the brake system
Continuous air escaping points to a leak that must be repaired before driving.
Question 6: Why must you drain moisture from the air tanks (unless equipped with an automatic drain)?
- To increase engine power
- To prevent water and oil from damaging the brake system (Correct answer)
- To improve fuel mileage
- To keep the tires inflated
Correct answer: To prevent water and oil from damaging the brake system
Draining tanks removes water and oil that can freeze or foul the brake system.
Question 7: The dual air brake system has separate air lines for the front and rear brakes primarily to provide what?
- Faster acceleration
- A backup so some braking remains if one system leaks (Correct answer)
- Better fuel economy
- Quieter operation
Correct answer: A backup so some braking remains if one system leaks
Dual systems ensure partial braking remains if one circuit loses air.
ELDT Vehicle Systems and Malfunctions 3
What is the purpose of the spring brakes (parking brakes) in an air brake system?