In Fig. 207 is shown the Mogul 6-ton rear spring, which is of the semi-elliptic double sweep type with plain ends. These ends fit between the webs of the frame bracket, which has a hardened steel plate resting on the spring. In this case the spring seat is also mounted on the axle spindle; however, in place of the usual box clip, four heavy holts with a T-shaped head are used. The bolts fit into grooves formed into the walls of the spring seat and the heads of the holts fit into rectangular holes cast into the seat. Two flat bars are used as a pressure block and are retained by washers and nuts. The front spring is connected to the frame at the forward end by an eve and a shackle bolt, while the rear end is plain and rests against a hardened plate on the bracket. The method of axle mounting is similar to the rear; however, clips are used in place of bolts, while the spring seat is a steel casting, which fits over the axle as shown in Fig. 208. The clips pass through holes in the seat proper which coincide with grooves cut into the upper flange of the axle. Tapered washers and nuts hold these together.
Fig. 208. Mogul 6-Ton Front Spring Mounting.
Fig. 209. Chase Underslung Spring Shackled at one End.
On the Chase worm-driven models, the rear springs (Fig. 209) pass under instead of over the axle, and also take both the torque and the driving thrust. For this reason it is necessary to rigidly connect the front end of the spring to the frame, while the rear end is shackled to compensate for elongation under load. Conditions are reversed in the axle mounting, as the pressure block is placed under the spring and the spring seat over it. These are held together by clips of U-shape which pass over the axle.
Fig. 210 depicts the full-elliptic front spring used on the I.H.C. 1.000-lb. vehicles. They are clipped to both the frame and the axle. This type of spring consists of two semi-elliptic members, one mounted above the other, and are connected at their ends by bolts. This type is also employed on the rear end of these vehicles; however, instead of rigidly connecting the upper member to the frame; this is pivoted on a shaft as shown in Fig. 211. A bracket is attached to the frame, through which the shaft passes. The upper spring seat pivots on this shaft and has the spring clipped to it as shown. The object of pivoting the upper end of the rear spring is to compensate for the spring play since the only connection between the axle and frame with this type of spring is through the radius rods.
Fig. 210. I.H.C. Full-Elliptic Front Spring.
Fig. 212 illustrates the three-quarter platform rear springs used on the heavy duty Mack trucks. The rear ends of the two side members are connected by double shackles consisting of two substantial U-shaped members which are hooked together, the same as on numerous horse-drawn vehicles.
Fig. 213 illustrates the overload or auxiliary spring which is usually a semi-elliptic member of the double sweep type. It is attached to a frame cross member at the center and the ends are free so that they may make connection with a separate spring when a predetermined load has been applied.
On the International Harvester Company's trucks, auxiliary springs are provided which take action at a time when the main springs are about to be overtaxed and prevent the load from coming in dead contact with the axle. These auxiliary springs are of the quarter-elliptic type and are attached to the brackets which take the driving strain at the front end of the spring. The rear ends of these auxiliary springs are. free to bear on the pressure blocks of the rear springs. This construction is illustrated in Fig. 214.
Fig. 211. Method of Mounting I.H.C. Full-Elliptic Rear Spring.
Fig. 212. Three-Quarter Platform Spring used on Mack Heavy-Duty Trucks.
Fig. 213. Overload Spring with Separate Seat.
The Knox Tractor employs an unusual method of suspension, Fig. 21"), which combines a cantilever and semi-elliptic spring at the rear end of the frame. Heavy semi-elliptic springs are attached to the rear axle with long clips and carry the fifth wheel of the trailer. There is no connection between these and the tractor frame, so that they carry the weight of trailer and load only. The tractor frame is mounted on a cantilever spring, having a pivot near its center and a shackle at the front end. The rear end bears on a seat clipped to the rear axle. This const ruction permits a flexible mounting for the tractor, and also the carrying of very heavy loads on the trailer. There is a great variety of methods of attaching the springs to the frame and rear axle. Several methods have been illustrated above, while the following gives an excellent idea of the attention that is being devoted to this vital point.
Fig. 214. I.H.C.Quarter Elliptic Overload Spring.
Fig. 215. Knox Tractor Cantilever Bear Spring.