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Difficulty: MediumBrake Failure

An operator driving a commercial straight truck equipped with hydraulic brakes approaches a downhill junction and presses the service brake pedal, only to discover that the pedal sinks completely to the floorboard with zero braking response. Which sequence of actions should the driver immediately take to regain control and safely stop the vehicle?

  1. A
    Shift the transmission into neutral to remove engine load, keep continuous light foot pressure on the floorboard, and wait for vehicle momentum to dissipate.
  2. Downshift to a lower gear, rapidly pump the brake pedal to rebuild hydraulic pressure, and modulate the parking brake while steering toward an open escape path.Answer
  3. C
    Maintain steady, light pressure on the depressed pedal without pumping, and apply periodic snub braking pulses to slowly bleed off highway speed.
  4. D
    Immediately pull the parking brake control fully to lock the drive wheels, while steering sharply away from the direction of any resulting vehicle skid.

Answer

Downshift to a lower gear, rapidly pump the brake pedal to rebuild hydraulic pressure, and modulate the parking brake while steering toward an open escape path.
When total hydraulic brake failure occurs (indicated by the pedal sinking to the floor), the standard CDL emergency procedure requires downshifting to harness engine braking, pumping the brake pedal repeatedly to rebuild hydraulic pressure, utilizing the independent parking brake to assist in deceleration, and seeking an escape path or ramp to bring the truck safely to rest.

Step-by-Step Solution

1
Downshift the transmission into a lower gear.
Harnesses engine compression braking to immediately slow the vehicle.
Lower gears utilize engine resistance to counteract vehicle momentum and downgrade acceleration.
2
Pump the brake pedal rapidly several times.
Generates and builds up residual hydraulic fluid pressure in the master cylinder and brake lines.
In hydraulic brake systems, pumping can often restore enough line pressure to actuate the wheel cylinders.
3
Apply the parking brake carefully while searching for an escape route or runaway truck ramp.
Applies a separate mechanical braking system to slow the vehicle to a complete stop off the main roadway.
The parking brake operates independently of the hydraulic fluid circuit and can stop the truck without risking a sudden lockup if applied with care.

Key Concept

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

Brake Failure

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