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Difficulty: MediumRetarders Usage and Cautions

During a haul on a rain-slicked highway, a driver notices the vehicle's drive wheels begin to slip every time the accelerator pedal is fully released. What action should the driver take regarding the retarder?

  1. A
    Increase the retarder setting to maximum to reduce foundation brake wear.
  2. Switch off the retarder completely to prevent a drive-wheel skid.Answer
  3. C
    Keep the retarder engaged while applying steady, continuous service brake pressure.
  4. D
    Leave the retarder engaged and downshift to a lower gear to increase engine drag.

Answer

Switch off the retarder completely to prevent a drive-wheel skid.
Retarders apply significant braking resistance exclusively to the drive axle whenever the throttle is released. On wet, icy, or snow-covered roads where tire traction is reduced, this resistance can cause the drive wheels to skid or slide, potentially causing a jackknife. Drivers must always turn off retarders in wet or slippery weather.

Step-by-Step Solution

1
Identify the operating condition and mechanism triggering the wheel slip.
The road is slippery from rain, and releasing the throttle automatically engages the auxiliary retarder, applying braking force exclusively to the drive wheels.
Retarders apply mechanical, hydraulic, or electrical resistance to the drive axle as soon as the throttle pedal is released.
2
Evaluate the safety hazard of auxiliary retarding on poor traction surfaces.
When drive wheels have limited traction, auxiliary retarding force easily overcomes available tire grip, locking or slipping the drive wheels into a skid or jackknife.
Commercial vehicle safety regulations require turning off retarders on wet, icy, or snow-covered roads.
3
Determine the required corrective driving action.
Turn off the retarder switch so the drive wheels can roll freely without unintended deceleration drag.
Switching off the system prevents drive-wheel lockup and restores directional stability.

Key Concept

Retarders must be switched off whenever road surfaces are wet, icy, or snow-covered because auxiliary drive-axle braking can induce a drive-wheel skid.
Estimated Time:1m 0s
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Topics

Retarders Usage and Cautions

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