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Question

Difficulty: MediumBrake Failure

A commercial motor vehicle driver navigating a secondary highway approaches a work zone and discovers that the hydraulic brake pedal drops straight to the floorboard without slowing the truck. Which action should the driver take first to attempt restoring braking pressure?

  1. A
    Activate the auxiliary engine retarder to full power to forcefully lock the drive axles regardless of road surface conditions.
  2. Pump the brake pedal rapidly multiple times to build up necessary hydraulic system pressure.Answer
  3. C
    Maintain steady, continuous pressure on the floorboard to allow automatic slack adjusters to mechanically compensate for excessive pushrod travel.
  4. D
    Rely solely on vehicle coasting distance under the assumption that total stopping distance excludes driver perception and reaction delays.

Answer

Pump the brake pedal rapidly multiple times to build up necessary hydraulic system pressure.
When a hydraulic brake pedal drops straight to the floorboard, rapidly pumping the pedal is the proven emergency technique to rebuild hydraulic line pressure. This action, combined with downshifting, gives the driver the best chance of restoring operational braking force before resorting to the parking brake.

Step-by-Step Solution

1
Diagnose the symptom of a hydraulic brake pedal dropping to the floorboard with zero resistance.
Recognizes a critical loss of hydraulic fluid pressure in the service brake circuit.
Immediate identification is essential to initiate hydraulic emergency recovery procedures.
2
Pump the brake pedal rapidly several times.
Compresses remaining fluid in the lines to restore sufficient operating pressure to stop the vehicle.
Pumping is the primary method to generate hydraulic pressure during sudden pedal drop.
3
Shift the transmission into a lower gear and prepare the parking brake as secondary measures.
Engages engine braking assistance and readies the mechanical parking brake if hydraulic pressure fails to build.
Provides layered redundancy to bring the commercial vehicle to a controlled standstill.

Key Concept

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

Brake Failure

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