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Question

Difficulty: EasyBrake Failure

While descending a steep mountain grade in a commercial vehicle, the driver experiences severe brake fade and total service brake failure. Which of the following is the correct emergency procedure to safely slow and stop the vehicle?

  1. A
    Pump the air brake pedal repeatedly at high speed to mechanically readjust the slack adjusters and pushrods.
  2. B
    Shift the transmission into neutral and engage the driveline retarder at maximum setting on slippery road surfaces.
  3. Downshift to a lower gear to maximize engine braking and steer into an escape ramp if one is available.Answer
  4. D
    Apply continuous, light pressure to the service brake pedal down the remaining slope to maintain current vehicle speed.

Answer

Downshift to a lower gear to maximize engine braking and steer into an escape ramp if one is available.
When service brakes experience severe fade on a downgrade, the correct procedure is to immediately downshift to a lower gear to maximize engine compression braking and look for an escape ramp or runaway truck ramp to bring the vehicle to a controlled stop.

Step-by-Step Solution

1
Recognize the loss of service brake responsiveness caused by brake fade on the downgrade.
Identify that the vehicle cannot be slowed using standard service brakes.
Immediate recognition ensures the driver does not waste critical seconds relying on ineffective overheated brakes.
2
Downshift the transmission into a lower gear to utilize engine compression braking.
Harness engine braking resistance to slow or stabilize runaway vehicle acceleration.
Engine braking provides mechanical resistance to the drivetrain without depending on friction linings.
3
Locate and steer into an available runaway truck escape ramp.
Bring the commercial vehicle to a controlled stop using the designated gravel bed or incline.
Escape ramps are specifically engineered to stop runaway commercial vehicles safely without risking a high-speed collision.

Key Concept

Emergency response procedures for brake fade and service brake failure on steep downgrades.
Estimated Time:45s
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Topics

Brake Failure

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