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Question

Difficulty: MediumBrake Failure

While approaching a signalized intersection on a two-lane rural highway, the operator of a hydraulic brake-equipped vehicle applies the service brake and feels the pedal sink entirely to the floorboard with no stopping resistance. Which of the following procedures should the operator perform to regain control and stop the vehicle safely?

  1. Downshift to a lower gear, pump the brake pedal rapidly to generate pressure, and carefully apply the parking brake if needed.Answer
  2. B
    Immediately activate the exhaust retarder to maximum power while shifting the transmission into neutral to prevent engine lugging.
  3. C
    Apply light, continuous snub braking using the trailer hand valve while maintaining cruising gear to cool the brake shoes.
  4. D
    Immediately lock the parking brake fully at highway speed and steer sharply toward the soft shoulder to initiate a controlled spin.

Answer

Downshift to a lower gear, pump the brake pedal rapidly to generate pressure, and carefully apply the parking brake if needed.
When hydraulic brakes fail and the pedal drops to the floorboard, downshifting uses engine compression to slow the vehicle, pumping the pedal three to four times can restore hydraulic pressure, and modulating the parking brake provides secondary mechanical stopping power.

Step-by-Step Solution

1
Recognize the specific failure mode as hydraulic loss rather than air brake fade.
Identifies that fluid pressure depletion requires physical displacement via the pedal.
Hydraulic systems can sometimes restore operational pressure through rapid pumping strokes.
2
Engage engine compression braking by downshifting into a lower gear.
The engine absorbs vehicle momentum and decreases road speed mechanically.
Engine braking functions independently of the wheel brake hydraulics.
3
Pump the brake pedal rapidly while preparing to modulate the parking brake.
Builds residual line pressure to apply the service shoes or provides a secondary mechanical friction source.
Careful application of the parking brake provides mechanical stopping power without locking the drive wheels.

Key Concept

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

Brake Failure

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