rear axle failure

A locking differential is a mechanical component, commonly used in off-road vehicles, that is designed to overcome the limitations of normal differentials by selectively locking the rotation of the wheels on an axle relative to one another, as if on a common shaft. In contrast to open differentials or limited-slip differentials found in many roadgoing cars, a locked differential forces both wheels to turn at the same speed, regardless of the traction (or lack thereof) available to each wheel individually.
When a differential is unlocked, each wheel is allowed to rotate at different speeds, which is desirable for negotiating turns, as the outside wheel travels a longer distance than the inside wheel. An open differential always provides the same torque to each wheel. Therefore, although the wheels may rotate at different speeds, they apply the same rotational force, even if one is entirely stationary, and the other rotating.
In contrast, a locked differential forces both wheels on a given axle to rotate at the same speed, regardless of the tractional conditions under either wheel. As such, each wheel can apply as much rotational force as the traction under it will allow, and the torques on each side-shaft will be unequal. A locked differential can therefore provide a significant traction advantage over an open differential, especially when the traction under each wheel differs significantly.
Differential locks may be engaged by an operator mechanically (via a lever or cable), hydraulically (fluid pressure moving a locking collar), or electrically (switch energizing a solenoid or actuator). They may also be activated automatically based on torque and speed thresholds.
Central differentials, which are found between the front and rear axles of many full-time four-wheel-drive vehicles, may also be locking differentials, providing similar tractional benefits.

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