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Question

Difficulty: MediumBrake Failure

As a commercial motor vehicle descends a long mountain grade, the driver experiences severe thermal brake fade, causing the service brakes to lose all stopping capability. With no runaway truck ramp available ahead, what is the safest procedure to bring the runaway vehicle to a halt?

  1. A
    Shift the transmission into neutral and immediately pull the parking brake control fully to lock all drive axle wheels.
  2. Downshift to the lowest possible gear, look for an open escape path off the roadway, and carefully modulate the parking brake without locking the wheels.Answer
  3. C
    Maintain continuous, maximum foot pressure on the service brake pedal while waiting for the overheated brake pushrods and drums to cool down.
  4. D
    Rapidly pump the service brake pedal while engaging the engine retarder at maximum capacity on slippery or degraded shoulder surfaces.

Answer

Downshift to the lowest possible gear, look for an open escape path off the roadway, and carefully modulate the parking brake without locking the wheels.
When service brakes fail completely due to severe thermal fade on a downgrade and no runaway ramp exists, the driver must downshift into lower gears to exploit engine compression braking, scan for an off-road escape path (such as an open field or gentle uphill side slope), and smoothly apply the parking brake without causing wheel lockup.

Step-by-Step Solution

1
Identify brake failure and utilize engine retarding power
Downshifting through lower gears forces the engine compression to absorb vehicle momentum without relying on overheated friction linings.
Engine braking provides reliable retarding force when mechanical service brakes suffer complete thermal fade.
2
Locate an alternative stopping path or escape route
Scanning ahead identifies soft shoulders, ascending side terrain, or open fields that can safely dissipate kinetic energy.
When designated runaway ramps are absent, natural terrain features must be used to arrest vehicle forward motion.
3
Apply auxiliary mechanical braking judiciously
The parking/emergency brake is modulated smoothly to slow the vehicle without inducing drive-wheel lockup or directional loss.
Abrupt parking brake application at highway speeds locks the drive wheels, causing immediate jackknifing or skidding.

Key Concept

Emergency response sequence and vehicle control during total thermal brake fade
Estimated Time:1m 15s
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Topics

Brake Failure

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