Fig. 67.—Driving Worm
The small gears that drive the bull gears are on the ends of the cross shaft, called the jack shaft, that carries the differential.
In the Fordson tractor the differential is built into the axle, as it is in an automobile, and power is applied by a worm. The worm is driven by the change speed gear, and is a screw meshing with a gear on the differential, whose teeth are cut at the proper angle to make them fit the threads of the worm. A worm, which is shown in [Figure 67], is always enclosed, and runs in oil.
CHAPTER IX
TRACTOR ARRANGEMENT
The uneven ground over which tractors must work requires the weight to be kept low, to prevent capsizing, and they are also built wide, for the narrower they are the more easily they tip over. They cannot be broad in front, however, for if they are the steering wheels cannot be swung enough to permit them to turn in the small circle that is desirable.
To give a small turning circle some tractors are built with the front of the frame raised enough to permit the wheels to cut under. Others use small steering wheels, but this is not desirable because small wheels will not run over rough ground as readily as large ones, and steering is difficult.
Fig. 68.—Tractor Arrangement
