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Question

Difficulty: HardBrake Failure

In the event of a sudden loss of service braking power at highway speeds, an operator should immediately pull the parking brake control valve to full lockup to achieve maximum emergency deceleration.

Answer: Answer

Answer

False
The statement is false because abruptly applying the parking brake valve at highway speeds causes the drive wheels to lock up completely. Sliding tires eliminate cornering and lateral stability, creating an extreme risk of jackknifing and rollover. Safe emergency procedure requires downshifting to utilize engine braking, locating an escape path, and applying secondary braking smoothly to prevent wheel lockup.

Step-by-Step Solution

1
Analyze the mechanical consequences of pulling the parking brake control valve at high speed.
Full application of the parking/emergency brake valve releases air pressure, allowing the heavy mechanical spring brakes to clamp the drive axle wheels with maximum force.
Spring brakes are designed for holding a parked vehicle or extreme emergency stopping, not modulated service braking.
2
Evaluate the directional stability and dynamics of the commercial vehicle.
Locking the drive axle wheels at highway speeds destroys directional stability and immediately causes a severe skid or jackknife.
Tires that are sliding lose their ability to provide lateral steering stability.
3
Determine the proper procedural sequence during a brake failure emergency.
The correct response is to downshift sequentially to utilize engine compression braking, search for an escape route or runaway ramp, and carefully modulate emergency braking without locking the drive wheels.
Vehicle control must be maintained while reducing speed safely.

Key Concept

Emergency Brake Application and Skid Prevention During Brake Failure
Estimated Time:1m 30s
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Topics

Brake Failure

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