By Michael Murguia – 11/30/16
Photos Credit: Barry J. Holmes
There is no doubt, lockers can transform even the mildly built rig into the equivalent of a mechanized off road tank, or if you prefer, “billy goat mode”.
While maneuvering and turning a vehicle, all four wheels want to have different turn rates. This is how a stock drivetrain is set up. Unfortunately, it allows all power to be transferred to the wheel with least resistance. If a tire comes off the ground or becomes “light”, it is going to spin while the other tires stop. You are stuck.
For the unindoctrinated, locking differentials are just that. They have many applications from drag strip racers, heavy equipment, and overland of road vehicles. If your “diff” is “locked”, it means both wheels on that axle are locked together and must turn at the same time. There are front, rear, and center lockers. In some vehicles (ehem FJ80), you have independent control of each locker.
Differential mechanics have been a part of automobiles since the beginning, and if you want bit of retrospective fun and a basic explanation of how differential systems work, this 1937 Chevrolet Motor Company film actually explains it nicely!
Do you NEED lockers for overlanding? Let’s look at three applications.
Headed to Ski-Mountain – Center Diff Lock
Lockers are not required in this scenario. Standard four wheel drive will do a great job at increasing traction. In this case you are on the freeway, on pavement and the road is probably slick, especially if it is icy-cold. You are probably going slower than the speed limit and want extra traction. In this case, the center diff lock will require your front and rear axles to receive the same amount of power, but all four wheels will still be independent, allowing them to turn at different rates while cornering. It provides added traction, without over-stressing the front and rear drivetrain, diff, and axels by locking those wheels on pavement.
Baja – Rear Diff Lock
If you are in the sand, speed is king. You need to keep your speed up to keep from getting bogged down. With higher speed comes higher risk, and ideally you have visibility. In combination with airing down to 10 or 12 psi, speed and traction will get you through the soft stuff. Why rear? You will be going at speed and turning in tight radius, and you don’t want to grind and stress the front. axel in tight radius. Also, you are not pulling or crawling over rocks, and your front tires are really acting as rudders. Rudders with traction mind you, but rudders. We like to say, you need the room to “suggest” where the vehicle should go, because you are going to slide a bit, even at low speeds. Lastly, and perhaps in more extreme cases, locked rear wheels are used for steering under power, or “drifting”. On soft surfaces, you can steer your vehicle by applying power to the rear when locked. It will cause your rear end to “slide out” and point the nose where you want to go. This does not work if your front is pulling at the same rate.
Rubicon – Front and Rear Locks
Here is where the terrain is more technical. If you are in four low, your center diff is most likely locked automatically by your system. That means, you are choosing between your front and rear diff locks. In principle, your choice is dictated for you. If a front tire is spinning, lock the front diff. Front and rear lockers are especially effective pulling or pushing out of a cross-axle stuck. Cross axle means a front and rear tire is able to slip. With normal 4WD, you are stuck. By locking the front or rear, you will move forward as long as you have traction. So why would you have to ever go “fully locked”? Usually, locking one differential will move you forward, however, if traction characteristics change significantly as you are moving forward, like when crawling up a shale slope, or moving over a number of basketball-sized rocks, you may want to be fully locked. A steep dirt incline with a combination of soft and hard pack also responds very well to being fully locked, allowing you to crawl up a hill slowly instead of using speed to get up the hill.
So, Do you NEED Lockers for Overlanding?
Just looking at the examples above, in the first case, lockers are not required. It will provide increased traction in some cases, but standard 4WD goes a long way toward keeping your vehicle on the road. In the next two cases, though “normal” for some, they are pretty extreme cases for most who are engaged in vehicle dependent travel. Even if you are going through the jungle, you are going slow and may be using your winch regardless of how much traction you do or don’t have.
Before embarking on a journey, you need to evaluate the requirements of your trip. What will you be asking your vehicle to do? One of our core principles with Overland Bound is that is doesn’t matter what you drive, HOWEVER, your vehicle needs to be equipped and capable for what you are asking it to do. It needs to be safe. Even so, we can’t think of any case where a locker is required. Without a locker, it means you may be digging out or winching out instead of driving out, and that means your journey will be slower, but not required. Many people overland in rigs similar to the 2WD Westfalia Vanagons and live in their rigs doing so. Lockers not included.
You DO NOT need lockers for Overlanding