Many people believe the myth that power from the engine will be directed to both drive wheels, and all four on a four-wheel drive vehicle. While to some extent there is truth to this, the power is never there when it is needed. Under normal driving circumstances, power can indeed go to both rear wheels and all four wheels on a four-wheel drive. However, if things get slippery or traction is not present, only the wheel with the least amount of traction will continue to spin. Obviously, trail drivers or race car operators do not like this scenario. This behavior is the reason they are sometimes referred to as "differentials," because they split the power or can operate independently. For this reason, especially in race car or trail truck applications, folks will install a locker into the differential(s).
Now that we understand how factory differentials work, let's see how the addition of a locker will change things. Both the right and left axles connect to the ring and pinion gears, which are turned by the driveshaft. In this manner, the vehicle is able to move forward and backward under power. While a stock carrier allows slippage between the right and left wheel to make turning and daily driving comfortable, a locker will literally "lock" the two axles together. Because of this design, the left and right wheels are always moving at the same speed and with equal power distribution between them. Power to each tire equally results in more rubber surface area on the ground and no slipping, which means far more traction whether on the street or off-road.
There are spring packs in the locker carrier which do allow for slight slippage at low speeds for turning, but the axles are locked together again the second power is applied, so driving a locked axle set on the street definitely takes some practice. Also, realize that because the axles are not allowed to turn at different speeds, tire chirping is a byproduct of implementing a locker. For this reason, tire wear will increase quite a bit if the vehicle is driven on the street very much. Although locked rear ends in street car applications will provide more traction in normal conditions, be aware that in wet weather conditions a locker can actually hurt performance, and cause the car to sway badly if traction is lost while giving it gas (burnouts). Unless you know your way around ring and pinions and how to set backlash when redoing axle gearing, it is recommended to let a professional install the locker for you.
