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Difficulty: HardUpshifting and Double Clutching

A driver operating a heavy tractor-trailer equipped with a manual transmission reaches the shift point while accelerating on an on-ramp. After pushing the clutch pedal down and moving the gear shift lever into neutral, what exact sequence of actions must the driver complete to properly finish upshifting?

  1. A
    Keep the clutch pedal held firmly to the floor in neutral while waiting for engine RPM to drop, then push the shift lever directly into the higher gear slot and release the pedal.
  2. Release the clutch pedal, allow engine RPM to decrease to the speed required for the next gear ratio, push the clutch pedal down again, shift into the higher gear, and smoothly release the clutch pedal.Answer
  3. C
    Release the clutch pedal, depress the throttle pedal momentarily to raise engine speed above the shift point, push the clutch pedal down again, and move the shift lever into the higher gear.
  4. D
    Press the clutch pedal completely to the floorboard to apply the clutch brake, pull the shift lever firmly into the higher gear immediately, and let the clutch pedal return quickly.

Answer

Release the clutch pedal, allow engine RPM to decrease to the speed required for the next gear ratio, push the clutch pedal down again, shift into the higher gear, and smoothly release the clutch pedal.
In unsynchronized manual commercial transmissions, double clutching requires letting the clutch pedal out in neutral so the engine slows the input shaft down to the exact rotational speed of the higher gear. Once the RPM drops to the appropriate level, pressing the clutch down again allows effortless engagement of the higher gear.

Step-by-Step Solution

1
Release the clutch pedal while the transmission remains in neutral.
The input shaft and countershaft re-engage with the engine flywheel.
Connecting the transmission input shaft to the engine in neutral allows the transmission rotational speed to be governed by the decelerating engine.
2
Wait for the engine speed (RPM) to drop to the level matching the vehicle road speed in the target gear.
Transmission input shaft speed slows to match the road speed of the higher gear.
Because higher gears turn fewer engine revolutions per wheel revolution, the input shaft must slow down to align gear teeth without grinding.
3
Depress the clutch pedal a second time.
The engine is temporarily disconnected from the synchronized drivetrain.
This relieves tooth pressure and allows smooth engagement of the shift collar.
4
Move the gear shift lever into the next higher gear and release the clutch smoothly while reapplying power.
The higher gear engages cleanly and the vehicle accelerates smoothly.
Synchronized rotation speeds allow the gear dogs to lock together without resistance or mechanical stress.

Key Concept

Double-clutch upshifting sequence and rotational synchronization
Estimated Time:1m 30s
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Topics

Upshifting and Double Clutching

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