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Question

Difficulty: MediumBrake Failure

A transit bus driver navigating a multi-lane suburban boulevard steps on the hydraulic brake pedal to slow down for an upcoming intersection, but the pedal drops entirely to the floor with no deceleration. What action should the driver immediately take to regain control and bring the vehicle to a halt?

  1. A
    Activate the driveline retarder at maximum intensity immediately, regardless of whether the pavement is wet or slippery.
  2. Pump the brake pedal rapidly to generate fluid pressure, downshift to a lower gear, and modulate the parking brake carefully if stopping power is not restored.Answer
  3. C
    Hold the brake pedal lightly and continuously against the floorboard to allow friction surfaces to cool down through steady contact.
  4. D
    Rely entirely on perception and reaction distance calculations to coast to a natural stop without downshifting or applying mechanical brakes.

Answer

Pump the brake pedal rapidly to generate fluid pressure, downshift to a lower gear, and modulate the parking brake carefully if stopping power is not restored.
In vehicles equipped with hydraulic brakes, a pedal sinking directly to the floorboard typically signifies a pressure drop or partial fluid loss. Rapidly pumping the brake pedal can generate sufficient hydraulic pressure to activate the wheel brakes. Concurrently downshifting harnesses engine compression to slow the vehicle, and cautiously modulating the parking brake provides secondary mechanical deceleration without causing a rear-wheel lockup.

Step-by-Step Solution

1
Diagnose the hydraulic brake failure symptom
Recognize that a pedal sinking to the floor indicates loss of hydraulic line pressure rather than air brake thermal fade.
Hydraulic systems operate on trapped fluid pressure, which may temporarily rebuild when pumped.
2
Execute the emergency hydraulic recovery sequence
Rapidly pumping the brake pedal creates immediate pressure cycles to push brake pads or shoes against drums/rotors.
Three to four rapid pumps often generate enough pressure to stop or significantly slow the vehicle.
3
Apply auxiliary stopping and vehicle control techniques
Downshift the transmission into lower gears to maximize engine braking, and apply the parking brake progressively to avoid wheel lockup.
Combining engine compression braking with mechanical parking brake friction brings the vehicle to a safe stop if hydraulic pressure cannot be rebuilt.

Key Concept

Hydraulic Brake Failure Recovery Procedure
Estimated Time:1m 0s
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Topics

Brake Failure

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