PCV Braking Systems and Technique 2 — Questions and Answers
Question 1: What is the purpose of an anti-lock braking system (ABS) on a PCV?
- To stop the vehicle more quickly
- To prevent the wheels from locking under heavy braking, allowing the driver to maintain steering control (Correct answer)
- To automatically apply the brakes in an emergency
- To reduce brake pad wear
Correct answer: To prevent the wheels from locking under heavy braking, allowing the driver to maintain steering control
ABS prevents wheel lock-up during heavy braking, allowing the driver to continue steering the vehicle.
ABS uses sensors on each wheel to detect when a wheel is about to lock. The system rapidly pulses brake pressure to maintain grip. The key benefit is retained steering control during emergency braking.
Question 2: When descending a long steep hill in a coach, you should primarily use:
- The footbrake continuously
- A lower gear and engine braking, supplemented by the exhaust brake or retarder (Correct answer)
- Neutral gear to save fuel
- The handbrake to control speed
Correct answer: A lower gear and engine braking, supplemented by the exhaust brake or retarder
Engine braking through a lower gear, combined with an exhaust brake or retarder, controls speed on descents without overheating the service brakes.
Continuous footbrake use on a long descent generates excessive heat, leading to brake fade. Select a low gear before the descent, use the exhaust brake or retarder, and only use the footbrake intermittently.
Question 3: What is brake fade?
- When brake pads wear out completely
- A reduction in braking efficiency caused by excessive heat in the braking system (Correct answer)
- When the brake fluid freezes in cold weather
- A gradual softening of the brake pedal over time
Correct answer: A reduction in braking efficiency caused by excessive heat in the braking system
Brake fade occurs when brakes overheat from prolonged use, reducing their ability to slow the vehicle.
Brake fade is caused by overheating from prolonged or heavy braking. Friction material becomes less effective, drums can expand, and brake fluid can boil creating gas bubbles.
Question 4: How does an exhaust brake work on a diesel PCV?
- It applies friction to the exhaust pipe
- It restricts exhaust gas flow, creating back pressure that slows the engine and drivetrain (Correct answer)
- It cuts fuel to the engine
- It diverts exhaust gases to the brakes
Correct answer: It restricts exhaust gas flow, creating back pressure that slows the engine and drivetrain
An exhaust brake restricts exhaust gas flow, creating back pressure that resists engine rotation.
An exhaust brake uses a valve in the exhaust system to restrict gas flow, creating back pressure that slows the engine. It works best in lower gears at higher RPMs.
Question 5: You notice the brake warning light illuminates while driving your bus. What should you do?
- Continue to the depot at the end of your shift
- Stop in a safe place as soon as possible and do not drive until the fault is investigated (Correct answer)
- Pump the brake pedal to build pressure
- Only stop if you notice reduced braking performance
Correct answer: Stop in a safe place as soon as possible and do not drive until the fault is investigated
A brake warning light indicates a potentially serious fault. You must stop safely and have the issue investigated.
The brake warning light can indicate low brake fluid, excessive pad wear, ABS malfunction, or air pressure loss. Stop at the nearest safe location and report the fault.
Question 6: What should you check about the air brake system during your daily walk-around check?
- Only that the air pressure gauge reads correctly
- Air pressure build-up rate, any audible air leaks, brake operation, and warning device function (Correct answer)
- Nothing - air brakes are maintenance-free
- Only the brake pedal feel
Correct answer: Air pressure build-up rate, any audible air leaks, brake operation, and warning device function
A thorough air brake check includes verifying pressure build-up, listening for leaks, testing brake operation, and checking warning devices.
Daily air brake checks should include: full pressure build-up, listening for air leaks, low-pressure warning device operation, footbrake firmness, and parking brake hold.
PCV Braking Systems and Technique 2
What is the purpose of an anti-lock braking system (ABS) on a PCV?