Shifting Gears
Shifting Gears tests manual-transmission control in a commercial vehicle. The exam expects smooth starts, correct gear selection, progressive shifting, double-clutching, and downshifting before a grade. Poor shifting causes driveline damage, loss of control on hills, and failed road tests.
Core rules
- Start in the lowest gear that moves the load smoothly; do not slip the clutch excessively.
- Shift progressively: upshift at the manufacturer's recommended rpm, not at the engine's maximum.
- Do not lug the engine or over-rev it. Both reduce control and increase wear.
- Double-clutch: clutch in, shift to neutral, clutch out, clutch in, shift to the next gear, clutch out. Match engine speed to road speed.
- Downshift before a downgrade. Select a gear that holds the load without continuous braking.
- Never coast in neutral. You need engine braking and immediate power.
- If you miss a gear, stop, reset, and start again rather than forcing it.
Worked example
A loaded tractor-trailer approaches a long 6% downgrade in high gear. The driver waits until the descent begins, then tries to downshift. Engine speed and road speed no longer match, the gear clashes, and the driver rides the brakes to control speed. The correct plan is to slow and downshift before the crest, choose a gear that holds the load, and use snub braking only as needed. Gear selection before the hill prevents brake fade.
Traps
- Coasting downhill in neutral to save fuel.
- Waiting until the downgrade starts to downshift.
- Upshifting at maximum rpm instead of progressive shift points.
- Holding the clutch down at a stop instead of using neutral and the brake.