Certain differentials are set up so that they limit the ability and tendency of sending power to any wheel that does not have traction in an open differential type of setup. Limited slip differentials (LSDs) help to direct the engine power away from the traction-less wheel and toward the other wheel on the same axle. Also known as a positraction differential, power is distributed evenly between both wheels on the axle when both have traction and the vehicle is traveling in a straight line. If one wheel starts to lose traction, the LSD will automatically increase power to the wheel that still has traction. This type of differential limits the torque loss which occurs when one of the wheels loses traction.
Another type of differential is set up to engage automatically whenever torque is being applied to that axle; both wheels are automatically engaged so that both provide power under torque. Called an automatic locking differential, it’s disengaged when torque is not present to an axle, such as when the clutch pedal is depressed. This allows for variance in wheel speeds when turns are being negotiated. While useful, automatic locking differentials may result in unusual or odd handling. Automatic lockers can require a bit of patience as you’re learning how the characteristics change during street driving as the differential locks and unlocks.
This differential, called an on-command locker, provides the benefits of both locking and open differentials. This differential is switch-operated and turns on a vacuum diaphragm or electric motor or by a cable or lever which operates the locker. If unengaged, an on-command locker performs exactly like an open differential. It lacks the unusual handling that may be present with automatic lockers. When engaged, on-command lockers lock the shafts of the axle and makes them act more like a spool which has no speed differential between the wheels on that axle.
Some vehicles have spools which lock the axle’s wheels together constantly and do not employ differentials at all. This type of setup is typically employed in vehicles intended for racing and harsh off-road use. Spools are generally only used in vehicles that have need of a strong, light rear-end setup.
E-locker differentials act like open differential until the situation calls for additional traction. With the push of a single button, the e-locker engages to solve nearly any traction issue. This type of differential is designed especially for 4WD vehicles to provide the ability to lock or unlock differentials as needed. The e-locker can perform as a full-lock and direct all available torque to each end of the axle evenly.
The last type of differential discussed here is the selectable locking differential, also known as an air locker. It’s engaged through a pneumatic switch operated by the driver. Air lockers provide the smooth street operation found with open differentials, as well as full-lock traction in situations where it’s needed. The number-one differential choice for rock crawling vehicles, air lockers can be employed in more than 100 differential functions.