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The leaf spring acts as a flexible beam on self-propelled vehicles and transmits the driving and breaking forces to the frame from the axle assembly. Leaf springs are semi-elliptical in shape and are made of high quality alloy steel. There are two types of leaf springs- single leaf and multileaf (fig. 8-11). The single leaf spring, or monoleaf, is a single layer spring that is thick in the center and tapers down at each end. Single leaf springs are used in lighter suspension systems that do not carry great loads. A multileaf spring is made up of a single leaf with additional leaves. The additional leaves make the spring stiffer, allowing it to carry greater loads. The most common type is the multileaf spring (fig. 8-12) that consists of a single leaf with a number of additional leaves attached to it using spring clips. Spring clips, also known as rebound clips, surround the leaves at intervals along the spring to keep the leaves from separating on the rebound after the spring has been depressed. The clips allow the springs to slide, but prevent them from separating and causing the entire rebound stress to act on the master leaf. The multileaf spring uses an insulator (frictional material) between the leaves to reduce wear and eliminate any squeaks that might develop. To keep the leaves equally spaced lengthwise, use a center bolt for the multileaf spring. The center bolt rigidly holds the leaves together in the middle of the spring, preventing the leaves from moving off center. Each end of the largest leaf is rolled into an eye, which serves as a means of attaching the spring to the vehicle. Leaf springs are attached to the vehicle using a spring hanger that is rigidly mounted to the frame in the front and the spring shackle in the rear, which allows the spring to expand and contract without binding as it moves through its arc. Bushings and pins provide the bearing or support points for the vehicle. Spring bushings may be made of bronze or rubber and are pressed into the spring eye. The pins that pass
Figure 8-10.- Coil springs.
through the bushings may be plain or threaded. Threaded bushings and pins offer a greater bearing surface and are equipped with lubrication fittings. Leaf springs are used on the front and rear of heavy-duty trucks and the rear of passenger vehicles and light trucks. Trucks that carry a wide variety of loads use an auxiliary or overload spring. This auxiliary spring (fig. 8-13) may be mounted on top of the rear springs and clamped together with long U-bolts, or it may be located under the axle separate
Figure 8-13.- Auxiliary spring. from the main spring. In either case, the ends of the spring has it own support brackets. When the truck is under a load, the auxiliary spring assumes part of the load when its ends contact the bearing plates or special brackets attached to the frame side rails. A large portion of six-wheel drive vehicles utilize a bogie suspension (fig. 8-14) which uses leaf springs. This suspension is a unit consisting of two axles joined by torque rods. A trunnion axle acts as a pivot for the drive axles and is supported by bearings that are part of the spring seat. The ends of each spring rest in the guide brackets bolted to the axle housings. Mounting the springs on central pivots enable them to distribute half of the rear load onto each axle. As a result, this type of suspension allows the vehicle to carry a much heavier load than a single axle without losing its ability to move over unimproved terrain. When one wheel of a bogie suspension is moved up or down because of an irregularity in the road, the spring pivots on the trunnion shaft and both ends of the spring deflect to absorb the road shock. This causes the load to be placed on the center of the spring resulting in equal distribution of the load to both axles. The torque rods ensure proper spacing and alignment of the axles and transmit the driving and braking forces to the frame. |
 
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