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Difficulty: HardBrake Failure

An urban delivery truck equipped with hydraulic brakes is approaching an active railway crossing at 35 mph when the driver depresses the brake pedal and feels it sink directly to the floor with zero deceleration. After an immediate attempt to pump the pedal generates no braking pressure, what is the most appropriate course of action to stop the vehicle safely?

  1. A
    Shift the gearbox into neutral and coast until natural rolling resistance stops the vehicle before the tracks.
  2. B
    Rely on automatic slack adjusters to take up excess pushrod stroke by repeatedly feathering the service brake treadle until mechanical contact is restored.
  3. Downshift sequentially through the transmission gears, modulate the parking brake while holding the release mechanism, and steer toward an open escape path.Answer
  4. D
    Activate the driveline retarder at maximum setting and steer onto wet roadway shoulders to scrub speed through tire friction.

Answer

Downshift sequentially through the transmission gears, modulate the parking brake while holding the release mechanism, and steer toward an open escape path.
When hydraulic brakes fail and pumping the pedal produces no pressure, the driver must step through emergency procedures: downshift through lower transmission gears to harness engine braking, apply the parking brake progressively while holding the release mechanism to avoid wheel lockup, and locate an escape route or open runoff area.

Step-by-Step Solution

1
Diagnose total hydraulic pressure loss after pedal pumping fails.
The driver confirms that primary hydraulic service braking is entirely unavailable.
When pumping the pedal fails to generate hydraulic line pressure, alternate slowing and stopping mechanisms must be deployed immediately.
2
Downshift progressively into lower gears.
Engine compression braking slows the vehicle driveline substantially.
Utilizing powertrain drag is the primary method to scrub kinetic energy when friction service brakes fail.
3
Apply the parking brake cautiously while keeping the release catch held open.
Emergency braking friction is applied to the wheels without locking them into an uncontrolled skid.
Modulating the parking brake lever prevents wheel lockup and preserves directional stability.
4
Scan for and steer toward an open escape route or soft ground.
The vehicle is directed away from hazardous obstacles, other vehicles, and active rail lines.
Finding an open runoff or soft roadside embankment allows the vehicle to come to a halt safely if friction braking alone is insufficient.

Key Concept

Emergency response procedures for total hydraulic service brake failure
Estimated Time:1m 30s
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Topics

Brake Failure

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