First, what is a differential and why do I really need them. They are the gear assemblies connected between the driving wheels (or front and rear axle in case of 4WD or AWD) that permit the wheels to turn at different speeds. This is especially important when going around a corner since the inside wheels turn more slowly than the outside wheel and the front and rear wheels turn at different speeds. Have you ever tried driving on dry pavement with the center diff lock (CDL) engaged? This is almost impossible. Rear or front differential lockers are no different from the CDL when talking about turning and differentials and must have a way to dis-engage during cornering. There are basically two types of traction devices . Locking and limited slip.
I think the first question that comes to every ones mind is; do I need a traction device? My Land Rover is four-wheel drive and I have a center locking differential. Your Land Rover will do just great on most roads and trails with out rear or front traction devices. If you have a Rover with traction control you are better off than one with no locker or traction device. The Land Rover Traction control works in conjunction with the ABS brakes. When one wheel starts to spin, the ABS is applied in short rapid pulses to the spinning wheel. This forces some of the torque to be transferred to the wheel that is not spinning providing forward movement to the vehicle.
But, for those of us that do not have traction control there is a distinct advantage to having at least a rear traction device of sorts. Think of it this way, with ân open front and rear differentials, even with the CDL engaged in certain conditions such as when you get cross axled (one front and one back wheels loose traction), you basically have a two wheel drive vehicle with the power going to the two wheels with least resistance. The one front wheel and one rear wheel spinning receive the power allowing you to loose traction and possibly being stuck. Remember, power (torque) flows to the wheel with least resistance.
By adding a traction device to the rear differential in the same situation you have a three wheel drive truck. Torque is then transferred to both back wheels. The rear wheel that has resistance (traction) now can propel the truck. This does not how ever help the front wheel with resistance, as power is still flowing to the wheel of least resistance. Adding a traction device to the front will give you four-wheel drive. This does not mean if one wheel looses traction, that wheel will help get you going. It just means that the wheel(s) with resistance will receive power helping the vehicle move forward.
There are many types and brands of traction devices for all types of vehicles. This includes Land Rovers. They range from the “Lincoln locker” (using a Lincoln welder to lock the spider gears (not recommended)) which we used in my stock car racing days, to locking differentials like the Detroit Locker®. Types like Detroit Locker® keep the wheels continually locked together when going straight. This provides torque to the left and right wheels while the wheels are rotating at the same speed. They unlock when one wheel turns faster than the applied torque such as turning. This is done with spring loaded drivers and meshing teeth that lock the axles together while the wheels are turning at the same speed. They unlock when one wheel spins faster than the opposite while turning.
There is also the limited slip differential like the Detroit Truetrac® . They provide a controlled amount of resistance, using gears, rather than clutches (used in other makes). When one wheel looses traction and starts to spin, the other wheel (with traction) receives sufficient power to keep the vehicle moving. This is transparent to the driver. Then there are the types that require interaction from the driver to engage like the ARB Air Locker. These provide an open differential during normal driving and a locked differential when switched on.
ARB lockers are used by many Land Rover owners for off road, in the front and rear of their rigs. They how ever are more expensive and require adding wiring, switches and an air pump to actuate the locker. When additional traction is need, the driver engages a switch that routes air to the locking mechanism in the differential engaging the locking device. I chose the Detroit locker for the rear of my Discovery based on conversations with a lot of off roaders. I have to admit most were Jeep people, along with the Alan at North Texas Rovers in Dallas. It has worked well for me. An other choice used by members of the Texas Rovers has been the Truetrac in the front and rear. This has proven a successful combination also.
I have been happy with my Detroit locker in the rear. It has made it possible for me to go through bumper deep mud (with A/T tires) and up steep rock ledges with little or no trouble. Places that normally proved difficult or impassable. See the article on Airstrip. Some things to remember when using a full time locked differential, they must dis-engage during cornering. The trick is not to keep power to the rear wheels. Making sharp corners on paved streets, such as in housing areas, if power is applied during cornering some time causes a loud metallic clunk sound as the unit dis-engages due to the rear wheels turning at different rates. On loose soil , with the window rolled down you may hear the in side tire scrub on the ground as there is not enough traction to allow the differential to dis-engage. These are arguments against the use of them on the paved road. These can be over come by re learning how you corner. Limited slip differentials like the TrueTrac do not have these quirks. But, in extreme off road situations they may hesitate engaging.