Differential Repairs & Overhauls

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A differential is more than just a mechanism for letting one wheel spin faster and travel further than the other, as is necessary when a vehicle is cornering. In simplest terms, a differential is a "torque equalizer".

 "Equal Torque" is not always a good thing, however. When one tire is completely airborne (or on very low-friction ice), for example, it requires very LITTLE torque to spin that wheel. The remaining tire (the one with traction) will receive equally little torque (twisting force) -- not even enough to spin it, usually. The Result?  -- No "go". The traction-less tire will spin TWICE as fast as it normally would, and the tire that does have traction won't spin at all. This is the characteristic behavior of an un-limited slip differential -- the most common type.

A "limited slip" differential uses a mechanical device to allow UNEQUAL torque to be applied to the two axle shafts under certain specific circumstances. The "triggering circumstance" in most cases is an increasing DIFFERENCE in the rotational speed of the two axle shafts. As this difference increases, a mechanism of some type (often a set of friction clutches) begins to engage in order to increase the torque to the wheel with greater traction. The wheels will still turn at unequal speeds; but both wheels will always turn SOME. "Slipping" isn't eliminated; it's merely "limited". The "Trac-Lock" is the most common limited slip differential used in trucks. The "Power-Lock" is also used.

A "locker" is different from a limited slip differential and could be called a "zero-slip" differential. Lockers have different ways of assuring that both axle shafts turn at precisely the same rotational speed when required -- despite the fact that the torque or twisting force required to turn them might be grossly un-equal (as when one tire is wedged in rocks and the other is airborne). The "ARB Air Locker" is triggered into this mode with the flip of a switch under the dashboard. The "Detroit Locker" and "Lock-Rite" Locker both "sense" unequal axle shaft motion mechanically, and automatically engage their locking features.

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