4WD BASICS: DIFF LOCK & DRIVE MODES
9 min · Free lesson · written lesson, video in production
After this lesson you know what 4H, 4L and diff locks each do, and you choose the right one before the terrain demands it.
The Technique
- What a diff does: it lets wheels turn at different speeds through corners. Off road, an open diff sends drive to the wheel with the least grip - which is why one wheel spins uselessly while you go nowhere.
- 4H: higher speeds on low-traction surfaces - gravel, dirt roads, sand. On part-time systems, never on high-grip bitumen: transmission wind-up damages drivelines.
- 4L: low range multiplies torque and engine braking. It is your crawl control for steep, rocky and soft ground. Select it before the obstacle - most vehicles need a stop and neutral to engage.
- Lockers: a rear locker keeps drive when a wheel lifts or unloads; a front locker adds more but makes steering wide and heavy. Unlock as soon as grip returns.
- Traction control: modern electronics do a lot. Learn what your vehicle has and how it interacts with lockers - some systems switch off when a locker engages.
- The habit that matters: read the terrain ahead and set the drivetrain early. Changing modes in the middle of a bog is too late.
Common Mistakes
Part-time 4WD left in 4H on bitumen. Fix: sealed road, 2H, every time.
- Reaching for 4L halfway up the hill. Fix: drivetrain set at the bottom.
- Locker left in through grippy turns, straining axles. Fix: unlock the moment it has done its job.
The Drill
An empty gravel area. Practise every mode change your vehicle has, per the manual, until each takes seconds without thinking. Then drive a tight circle at walking pace on loose ground with the rear locker in, and feel what it does to the steering.
Engagement rules come from your vehicle's manual, not forums. Locked steering runs wide - learn it at walking pace. On slopes, low range is selected before the descent, never mid-slope.
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