CDL Air Brakes TestUsing Air BrakesEasy
A driver is attempting to stop a commercial vehicle with air brakes and notices a significant delay between pressing the brake pedal and the brakes actually engaging. This phenomenon is known as:
- AHydroplaning.
- BCompressor inefficiency.
- CBrake fade.
- DBrake lag.
Show answer & explanationAnswer & explanation
Correct answer: D. Brake lag.
The delay between the driver pressing the brake pedal and the brakes engaging is called brake lag. It is an inherent characteristic of air brake systems due to the time it takes for air pressure to travel through the lines and apply the brake chambers.
Why the other options are wrong
- A. Hydroplaning is when tires lose contact with the road due to water, unrelated to brake system response time.
- B. Compressor inefficiency would affect the system's ability to build and maintain pressure, not the immediate response time once pressure is available.
- C. Brake fade is the loss of braking power due to overheating, not a delay in initial application.
Brake Lag
The inherent time delay in an air brake system between when the driver presses the brake pedal and when the brakes actually begin to apply.
- Characteristic of air brake systems.
- Caused by air travel time.
- Increases stopping distance.
- Must be accounted for by drivers.
Memory trick: Lag is the wait, fade is the heat.