Overload springs may either be of the leaf or coil type, and so arranged as to act only when the load on the main springs reaches a certain amount. Below this load they do not contact with their seat or wear plate. The wear plate may be a separate platform, as illustrated in Fig. 213, or it may be formed integral with the pressure block. When coil springs are used, they are made of square section, attached either to a frame cross member or the axle. Two such springs arc used, one on each side.
The general desire to prevent breakage at the center is seen in the liberal proportion of the pressure blocks and spring clips. They represent the efforts of the various makers to provide a rigid connection between the spring and the sent. There is a growing tendency to employ the U-shaped spring clip which tends to exert an equal hold on each side of the spring, consequently the tension is equally distributed when the nuts are drawn up tight. They are made up of steel that will not easily become brittle under vibration.
Fig. 223. Fulton Three Point Front Shackle.
In most cases the spring eyes are bushed with phosphor-bronze or steel and shackle bolts are hardened and ground. The object of the bustling, of course, is to provide some means to renew the wearing surface. The bolts are Working continuously and will wear out quickly if they are allowed to remain dry. This lubrication is effected by grease cups which communicate with a hole in the bolt that permits the lubricant to reach the wearing surface.
Rear Spring and Shackle Assembly.
Front Spring and Shackle Assembly.
Fig. 224. Wick Oiling System on the La France 2-Ton Truck Spring Shackles.
In order to simplify maintenance some makers provide a wick oiling system for the spring shackles as illustrated in Fig. 224. This particular illustration depicts the La France construction, while the Fageol and Military class B vehicles are also provided with similar wick oiling systems. On the rear spring shackles oil reservoirs are cast integral with the shackles and wicks are inserted through drilled holes which feed the oil to the various bearings by capillary attraction. On the front springs the frame bracket carries the reservoir and a wick feeds oil to the upper pin which is hollow, thus permitting the oil to flow by gravity to the lower shackle pin or bolt.
Although friction between the spring leaves is desirable to an extent, yet it is necessary to keep the leaves lubricated when they bear against one another. This provision is usually made by the spring maker, and in most cases it is necessary to pry the leaves apart and introduce the lubricant with a knife.