Heres an exploded view of what makes a differential a differential. These parts allow your Mustang to turn right and left without tire scrub, so to speak. They allow the rear wheels to operate independently. The pinion shaft (A) supports the pinion gears (E). The tension pin (B) retains the pinion shaft. Side gears (C) are tied to the axle shafts. Thrust washers (D) are side bearings for the side gears. Thrust bearings for the pinion gears (F) give these gears something to bear against.