LGV Braking Systems 2 — Questions and Answers
Question 1: What is the correct procedure if the low air pressure warning activates while driving?
- Pump the brake pedal rapidly to build up pressure
- Stop as soon as safely possible, do not continue driving until the fault is identified and fixed (Correct answer)
- Continue driving slowly
- Turn off the warning light and continue
Correct answer: Stop as soon as safely possible, do not continue driving until the fault is identified and fixed
If the low air pressure warning activates, the driver must stop as soon as safely possible. Continuing to drive with low air pressure risks total brake failure and the automatic application of spring brakes at speed, which could cause loss of control.
Question 2: What is anti-compound on a braking system?
- A cleaning fluid for brake components
- A mechanism that prevents the service brake and spring brake from being applied simultaneously on the same wheel (Correct answer)
- A type of brake pad material
- An anti-rust coating on brake drums
Correct answer: A mechanism that prevents the service brake and spring brake from being applied simultaneously on the same wheel
Anti-compound prevents the simultaneous application of both the service brake and spring brake on the same wheel, which could generate excessive force and damage brake components. When the parking brake is applied, the anti-compound device releases the service brake pressure.
Question 3: What should a driver check regarding brakes during a daily walkaround?
- Nothing — brakes are only checked during annual tests
- Air pressure build-up rate, warning devices, air leaks (listen), brake hose condition, and brake disc/drum condition (Correct answer)
- Only the colour of the brake fluid
- Only whether the brake pedal moves
Correct answer: Air pressure build-up rate, warning devices, air leaks (listen), brake hose condition, and brake disc/drum condition
During the daily check, the driver should verify that air pressure builds up correctly, warning devices function, there are no audible air leaks, brake hoses are not damaged or chafing, brake discs/drums are not excessively worn or cracked, and the handbrake holds the vehicle.
Question 4: What is the purpose of the trailer emergency line (red coupling)?
- To supply electrical power to the trailer
- To automatically apply the trailer brakes if the trailer separates from the tractor unit (Correct answer)
- To supply air for the trailer air suspension
- To provide heating to the trailer
Correct answer: To automatically apply the trailer brakes if the trailer separates from the tractor unit
The emergency line (red coupling head) maintains air pressure in the trailer's emergency relay valve. If the trailer separates from the tractor, this line loses pressure, causing the emergency relay valve to apply the trailer brakes automatically, bringing the trailer to a halt.
Question 5: What is brake hysteresis?
- The sound brakes make when applied
- The difference between braking force during application and release — important for smooth, controlled braking (Correct answer)
- A type of brake disc
- The time taken to replace brake pads
Correct answer: The difference between braking force during application and release — important for smooth, controlled braking
Brake hysteresis is the difference between the braking force during brake application and during brake release at the same pedal pressure. Good hysteresis provides smooth, progressive control. Poor hysteresis causes 'snatchy' brakes that are difficult to modulate.
Question 6: Why might brakes pull to one side during braking?
- This is normal behaviour for all HGVs
- Uneven brake adjustment, a seized caliper, or different brake pad materials on opposite sides can cause uneven braking (Correct answer)
- Because the steering wheel is on the right
- This only happens in wet weather
Correct answer: Uneven brake adjustment, a seized caliper, or different brake pad materials on opposite sides can cause uneven braking
Braking to one side (brake pull) is caused by uneven braking force across the axle. This can result from unequal brake adjustment, a seized or sticking caliper, contaminated brake pads, or different pad materials on opposite sides. It is a dangerous condition requiring immediate attention.
LGV Braking Systems 2
What is the correct procedure if the low air pressure warning activates while driving?