Most heavy trucks use a multi-speed manual transmission, sometimes with a range selector that doubles the number of gears available.
- Match the gear to the load and the grade: a heavier load or a steeper hill needs a lower gear.
- Start in a low gear so the engine has enough power to get a loaded truck rolling without straining.
- Going downhill, select a low gear before you start the descent and let engine compression help control speed. Trying to shift down partway down a steep grade can leave the truck out of gear and accelerating.
Some trucks have a differential lock that ties the drive wheels together for traction on slippery ground. Use it only at low speed and turn it off once back on good pavement.
Common mistake: relying on the service brakes alone to control speed on a long downgrade. Continuous braking overheats the brakes, use a low gear and engine braking instead.
Recall: Why should you choose a low gear before starting down a steep hill rather than partway down?