in the heavy steam lorries, means are provided for throwing the differential gear out of action.
On many cars the bevel wheels of differential gear were too small in diameter, and hence there was insufficient room to get in pins of sufficient size to carry the pinions h, and rapid wear and breakage took place. In any case it is necessary to have ample diameter for these parts, and to see that they are kept well oiled, not only at the pins and gear teeth but at the centre of the axle, where the two parts are joined by means which allow them to rotate differentially on a centre pin and in the bearings in the differential gear-box which surrounds the wheel j. This box is not shown in the diagram, fig 4. The dotted lines at m indicate the bevel pinion on the spindle l., which is driven through a jointed rod by the motor. The means of transmission of the power to this spindle have been described in other chapters. The automobilist should occasionally jack up the rear of the car so that both drivers are free of the ground, so as to see that the wheels run equally free when either wheel is held, thus testing the free working of the differential gear, finding slack if it exists, and testing generally the condition of the gear and connections.
Steering Gear.—The loss of a ship's rudder is a small loss comparatively with that of the breakage or carrying away of an essential part of the steering gear of a motor carriage, especially of a high-speed car. The ship will continue to float and in most cases the stopping of the engines removes immediate danger from collision. With a broken steering arm or connecting-rod a car with its occupants may be hurled into a ditch, or ravine, or river before the driver has realised what has happened, and long before the brakes could do any good. The first provision against the helplessness that must, and the disaster that probably would, follow broken or disconnected steering gear, is sufficient strength in the parts. It should be as direct and simple in arrangement as possible, because least liable to disarrangement and because gear with chains and short rods and connections through springs have so many
