Differential gear, in automotive mechanics, gear arrangement that allows power from the engine to be transmitted to a pair of traveling wheels, dividing the force equally between them but permitting them to check out paths of different lengths, as when turning a corner or traversing an uneven road. On a straight road the wheels rotate at the same velocity; when turning a corner the outside wheel offers farther to proceed and will turn faster than the inner steering wheel if unrestrained.

The elements of the Ever-Power differential are demonstrated in the Figure. The power from the tranny is delivered to the bevel band Differential Gear equipment by the drive-shaft pinion, both of which are kept in bearings in the rear-axle housing. The case can be an open boxlike structure that is bolted to the ring gear and contains bearings to support one or two pairs of diametrically reverse differential bevel pinions. Each wheel axle is mounted on a differential side equipment, which meshes with the differential pinions. On a straight road the wheels and the side gears rotate at the same acceleration, there is no relative motion between your differential part gears and pinions, plus they all rotate as a unit with the case and ring gear. If the automobile turns left, the right-hand steering wheel will be forced to rotate faster than the left-hand wheel, and the side gears and the pinions will rotate relative to each other. The ring gear rotates at a velocity that is add up to the mean speed of the left and right wheels. If the wheels are jacked up with the transmission in neutral and one of the wheels is turned, the opposite wheel will submit the opposite path at the same velocity.

The torque (turning second) transmitted to both wheels with the Ever-Power differential is the same. Consequently, if one steering wheel slips, as in ice or mud, the torque to the other steering wheel is reduced. This disadvantage can be overcome relatively by the use of a limited-slip differential. In one edition a clutch connects one of the axles and the band gear. When one wheel encounters low traction, its inclination to spin is resisted by the clutch, hence providing better torque for the various other wheel.
A differential in its most basic form comprises two halves of an axle with a equipment on each end, connected jointly by a third gear making up three sides of a square. This is generally supplemented by a 4th gear for added strength, completing the square.