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Difficulty: MediumRetarders Usage and Cautions

When operating a commercial vehicle on wet, icy, or snow-covered roads, why is a driver required to turn off the auxiliary retarder?

  1. A
    Water and road spray entering the wheel hub assemblies will cause the retarder mechanism to overheat.
  2. B
    Continuous retarder engagement on slippery surfaces depletes compressed air reserves required for the foundation service brakes.
  3. The retarder applies braking force only to the drive axles, which can cause the drive wheels to lose traction and initiate a serious skid.Answer
  4. D
    The retarder automatically cuts engine fuel delivery and stalls the motor whenever tire slippage is detected.

Answer

The retarder applies braking force only to the drive axles, which can cause the drive wheels to lose traction and initiate a serious skid.
Auxiliary retarders apply braking resistance exclusively to the drive wheels. When roadway friction is low due to rain, ice, or snow, this concentrated retarding torque can easily cause the drive wheels to lose grip, leading to a drive-wheel skid or jackknife. For this reason, drivers must switch off retarders whenever roads are wet or icy.

Step-by-Step Solution

1
Identify the operating principle and axle distribution of auxiliary retarders.
Auxiliary retarders provide deceleration power exclusively through the vehicle's drive axles rather than distributing force across all wheels.
Commercial vehicle retarders (engine, exhaust, hydraulic, or electric) work directly through the driveline connected to the drive wheels.
2
Evaluate the effect of concentrated retarding force on low-traction road surfaces (wet, icy, or snowy).
When tire-to-road friction is reduced, the retarding torque on the drive wheels can easily exceed available traction, causing the drive wheels to slip or lock up.
Commercial driver regulations mandate turning off retarders in wet or icy conditions to prevent drive-wheel skids and trailer jackknifing.

Key Concept

Drive-Axle Skid Hazards from Retarder Use on Slippery Surfaces
Estimated Time:1m 0s
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Topics

Retarders Usage and Cautions

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