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Difficulty: MediumBrake Failure

A commercial driver approaching a signalized intersection in a truck equipped with hydraulic brakes presses the brake pedal and feels zero resistance as it sinks directly to the floor. Which action should the driver take first to attempt to restore braking pressure?

  1. A
    Engage the auxiliary retarder system to maximum power to replace the lost service braking capability.
  2. Rapidly pump the brake pedal several times in quick succession to generate fluid pressure.Answer
  3. C
    Shift into neutral and rely on natural rolling resistance to cover the remaining stopping distance.
  4. D
    Hold the pedal down firmly against the floorboard to allow automatic slack adjusters to reset pushrod travel.

Answer

Rapidly pumping the brake pedal several times in quick succession to generate fluid pressure.
When a hydraulic brake pedal drops to the floor with zero resistance, the driver should immediately pump the brake pedal rapidly. Pumping can compress air pockets or redistribute remaining brake fluid in the master cylinder to generate enough hydraulic pressure to slow or stop the commercial vehicle.

Step-by-Step Solution

1
Recognize the specific failure mode of a hydraulic brake system when pedal resistance collapses.
Identified that the pedal sinking to the floor indicates sudden hydraulic pressure loss or fluid displacement.
Commercial driving emergency procedures dictate distinct initial responses for hydraulic systems versus air brake systems.
2
Execute the primary recovery procedure for hydraulic brake systems.
Pumping the pedal rapidly acts upon the master cylinder to build up remaining fluid pressure in the braking lines.
Pumping often creates sufficient pressure to bring the vehicle to a safe halt before secondary emergency measures (downshifting or parking brake) are necessary.

Key Concept

Hydraulic Brake Failure Immediate Response Protocol
Estimated Time:1m 0s
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Topics

Brake Failure

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