Air Brake Test Air Brake Maintenance & Troubleshooting 2 — Questions and Answers
Question 1: What causes glazed brake linings and how does glazing affect braking performance?
- Moisture exposure causing surface rust — temporarily reduces braking until rust wears off
- Overheating from excessive braking — creates a hardened, low-friction surface that reduces stopping power (Correct answer)
- Oil contamination from an axle seal leak — has minimal effect on brake performance
- Normal use over high mileage — slightly improves brake modulation and feel
Correct answer: Overheating from excessive braking — creates a hardened, low-friction surface that reduces stopping power
Overheated brake linings develop a glassy, hardened surface with significantly reduced friction coefficient, weakening braking force.
Question 2: What is the most common cause of air brake system failure?
- Air compressor overload from continuous heavy-duty braking
- Brake lining wear reaching minimum thickness specification
- Air leaks that allow system pressure to drop below safe operating levels (Correct answer)
- Governor valve malfunction causing uncontrolled pressure cycling
Correct answer: Air leaks that allow system pressure to drop below safe operating levels
Air leaks are the leading cause of air brake failure because even small leaks can eventually reduce pressure below the minimum needed for safe braking.
Question 3: How can you detect an air leak in the brake system during a pre-trip or static inspection?
- Listen for hissing sounds and watch the pressure gauge for unexplained drops with engine off (Correct answer)
- Check the air filter housing for moisture accumulation or visible water
- Inspect the compressor drive belt for cracking or tension loss
- Measure brake drum temperature immediately after driving to locate hot spots
Correct answer: Listen for hissing sounds and watch the pressure gauge for unexplained drops with engine off
Air leaks produce audible hissing sounds and cause measurable pressure drops visible on the dash gauge when the engine is not running.
Question 4: You notice the air pressure gauge dropping slowly while the vehicle is parked with the engine off. What does this indicate and what should you do?
- This is normal — small pressure losses while parked are expected and acceptable
- This indicates an air leak that must be found and repaired before the vehicle is operated (Correct answer)
- Start the engine immediately to rebuild pressure before the warning buzzer activates
- Drain and refill all air tanks to reset the system before departing
Correct answer: This indicates an air leak that must be found and repaired before the vehicle is operated
Pressure should hold steady when parked; a slow drop confirms air is escaping through a leak that must be repaired before safe operation.
Question 5: What problems does water accumulation in air tanks cause, and how is it prevented?
- Corrosion of internal components and freeze-ups in cold weather — prevented by draining tanks daily (Correct answer)
- Excess system pressure — prevented by more frequent governor pressure cycling
- Compressor overheating — prevented by replacing the inline air filter more often
- Brake fade on steep grades — prevented by installing ventilated brake drums
Correct answer: Corrosion of internal components and freeze-ups in cold weather — prevented by draining tanks daily
Water condenses in air tanks and causes internal corrosion and can freeze in cold weather, blocking air lines and valves.
Question 6: What is the function of the air dryer in the air brake system?
- To cool compressed air before it enters the storage tanks to reduce pressure
- To remove moisture and contaminants from compressed air before it reaches the tanks (Correct answer)
- To regulate maximum system pressure as a backup to the governor valve
- To prevent the air compressor from overloading during heavy brake use
Correct answer: To remove moisture and contaminants from compressed air before it reaches the tanks
The air dryer filters water vapor and contaminants from compressed air, protecting tanks, valves, and brake components from corrosion and freeze-ups.
Air Brake Test Air Brake Maintenance & Troubleshooting 2
What causes glazed brake linings and how does glazing affect braking performance?