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Difficulty: Very hardSkid Control and Recovery

You are navigating a commercial combination vehicle down a rain-slicked, 4% grade. To prevent service brake fade, you activate the engine retarder. Shortly after, the tractor's rear drive axles lose traction, causing the back of the cab to swing rapidly outward to the right, initiating a tractor jackknife. Which multi-step sequence represents the correct mechanical and procedural recovery for this specific crisis?

  1. Immediately turn off the engine retarder, depress the clutch pedal, and rapidly steer the front wheels to the right.Answer
  2. B
    Keep the retarder engaged, lightly apply the trailer hand valve to pull the combination straight, and steer to the left.
  3. C
    Downshift to maximize engine braking on the drive wheels, release all service brakes, and steer away from the swinging rear.
  4. D
    Apply firm pressure to the service brakes to drastically reduce your momentum before the upcoming curve, while locking the steering wheel straight ahead.

Answer

The correct recovery sequence is to immediately deactivate the engine retarder, push in the clutch, and steer to the right (into the direction of the skid).
This multi-step sequence directly addresses the mechanical root cause of the emergency and applies the proper physical recovery techniques. Turning off the retarder and depressing the clutch stops the drive wheels from braking, allowing them to roll and regain traction. Steering to the right (into the skid) counteracts the rear of the tractor swinging out, realigning the combination without inducing a secondary slide.

Step-by-Step Solution

1
Identify the root cause of the traction loss.
The engine retarder applied excessive braking force to the drive wheels on a slippery surface, causing them to lock or slip.
Engine retarders only slow the drive wheels, which can easily overcome the available traction on rain-slicked roads.
2
Remove the braking force from the drive axles.
Turn off the engine retarder and fully depress the clutch pedal.
Depressing the clutch disconnects the engine from the drivetrain, eliminating all engine compression drag and allowing the drive wheels to roll freely to regain lateral grip.
3
Counter-steer to realign the tractor with the trailer.
Steer quickly to the right.
Because the rear of the tractor is swinging to the right, the driver must steer to the right (into the skid) to bring the front of the vehicle back into alignment with the swinging rear.

Key Concept

Drive-Wheel Skid Recovery and Engine Drag Management
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Topics

Skid Control and Recovery

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