The bevel drive pinion, connected to the pinion shaft, drives the bevel drive gear and the differential case to which it is attached. Therefore, the entire, differential case always rotates with the bevel drive gear whenever the pinion shaft is transmitting rotary motion. These trunnions are attached to the walls of the differential case. The differential pinions mesh with the side gears, as did the spider and side gears in the differential described in chapter 11. The axle shafts are splined to the differential side gears and keyed to the wheels.
Power is transmitted to the axle shafts through the differential pinions and the side gears.
When resistance is equal on each rear wheel, the differential pinions, side gears, and axle shafts all rotate as one unit with the bevel drive gear. In this case, there is no relative motion between the pinions and the side gears in the differential case. That is, the pinions do not turn on the trunnions, and their teeth will not move over the teeth of the side gears. When the vehicle turns a comer, one wheel must turn faster than the other. The side gear driving the outside wheel will run faster than the side gear connected to the axle shaft of the inside wheel.