Locked ‘n’ Loaded

The differential lock is the holy grail in off-road equipment. 

A four-wheel-drive vehicle is only as good as the power it can transmit from its power plant to the ground. Traversing rugged unmaintained trails requires all hands on deck when it comes to traction, and many people will be surprised to know that your four-wheel-drive vehicle, is not actually powering all four wheels.Differentials are placed in between the tires on an axle and allow for the inside and outside tires to move at different speeds while turning. All arcs in a circle are different lengths, so when you turn, all four tires on your vehicle are moving at different speeds and different distances. Without differentials, there would be a mechanical bind in the driveline that would cause unpredictable handling and potentially damage.This aid on the street presents a major difficulty off the beaten path as an open differential with no traction aid, means that really only one front tire and one rear tire are receiving traction. Modern vehicles use traction aids in the form of the ABS system to assist the torque transfer in the differentials by not giving a path of least resistance for the torque to travel. The computer modulates the individual brakes on tires that are spinning to try and shunt that power to the ones that are not.

Some vehicles use automatic mechanical traction aids like limited-slip differentials. These differentials have clutch packs or helical gears that operate on centrifugal force. If there is a large and sudden speed difference between the left and right axle shafts, the clutch packs will engage and lock the two sides together. But because this is only after a slip is detected, valuable energy is lost in that first few moments, and because the clutch packs are held together by friction, it is not a true mechanical lock and slippage can occur.

This is all solved by the holy grail of traction aids, the locker. A differential lock is exactly what it sounds like, it’s a mechanical lock of both sides of the axle. You remove the ability for the tires to move at different speeds within the circle during a turn. On vehicles with front and rear differential lockers, true four-wheel drive is achieved and you are transmitting 100 percent of the engine output to the tires.

This means that if you are traversing rough terrain that requires a high amount of articulation, and one of your tires leaves the ground, the locker will make sure that that power is being transmitted to the tire still on the ground. The same reason we want open differentials on the street—for predictive handling —is the same reason we want locked differentials off-road. Predictive handling that doesn’t require excessive force to achieve results.