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Difficulty: HardRetarders Usage and Cautions

As rain begins to coat the roadway surface during a haul, what immediate adjustment must be made to the vehicle's retarder system, and what hazard does this prevent?

  1. A
    Reduce the retarder to its lowest power stage, preventing service brake overheating while keeping auxiliary braking torque within safe traction limits.
  2. B
    Keep the retarder fully engaged, because retarder braking torque is distributed evenly across all tractor and trailer axles to prevent jackknifing.
  3. Turn the retarder completely off, because retarder braking force applies only to the drive wheels and can cause them to lose traction, resulting in a drive-wheel skid.Answer
  4. D
    Maintain retarder engagement while manually feathering the trailer hand brake to balance deceleration forces across the combination vehicle.

Answer

Turn the retarder completely off, because retarder braking force applies only to the drive wheels and can cause them to lose traction, resulting in a drive-wheel skid.
When road surfaces are wet, icy, or covered with snow, retarders must be turned completely off. Because retarders apply braking power only to the drive wheels, any auxiliary drag on low-friction pavement can cause the drive wheels to lose traction, leading to an immediate drive-wheel skid or jackknife.

Step-by-Step Solution

1
Identify the vehicle's current road condition and auxiliary braking configuration.
The roadway is becoming wet and slick due to rain, significantly reducing available tire-to-road friction.
Available road friction dictates the maximum braking force drive wheels can sustain before slipping.
2
Analyze how retarders apply deceleration force to the vehicle.
Retarders apply supplemental braking torque exclusively to the drive axle wheels rather than across all tractor and trailer axles.
Concentrating auxiliary retarding force on drive axles when road friction is low easily exceeds tire grip limits.
3
Determine the required driver action and safety outcome.
The driver must switch the retarder completely off on wet, icy, or snow-covered roads.
Eliminating unmodulated auxiliary drag on drive tires preserves lateral traction and prevents drive-wheel skids or jackknifing.

Key Concept

Retarder disengagement on low-traction road surfaces to prevent drive-wheel skids
Estimated Time:1m 30s
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Topics

Retarders Usage and Cautions

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