Q: What is a leaf spring?

A leaf spring is a suspension support made up of long metal strips bent into an arc or elliptical shape with multiple pieces attached one on top of another as determined by the overall weight the spring is to support.

These type of springs have been used since medieval times and were known by many other names including carriage springs. These springs are used today in some automotive vehicles but are primarily used in truck and trailers. They support the weight of the assembly by allowing the load to be carried safely while traveling on or off road. Each individual spring element or leaf is combined in different lengths and the overall number of leaf components depend on the rated weight limit of the particular vehicle.

They are indexed or kept in alignment for assembly using a center bolt and bound together with clips that secure the leaves. The entire assembly is joined to the frame of the vehicle by bolts through metal brackets called shackles, which reside in hangers bolted or welded to the frame of the vehicle.

The main signs of spring failure include squeaking noise when the vehicle is going over bumps or cracking sounds if one or more leafs has broken. The rebound clips can rust out and allow the spring elements to shift, which can make them hit or contact on the frame of the vehicle. Also, inside the shackle ends are bushings which support the assembly. These bushings can wear, causing noise or shifting of the springs which can be felt when starting out or stopping. Like cylindrical springs they are exposed to repeated compression and relaxation which will weaken over time. This causes sagging on the side of the axle they are attached to as the resultant wear may not be even on each spring.

The proper repair for damaged or defective springs is to replace them as a set on whatever axle they are on. By doing so, the ride height, cushion, or stability they offer is evenly returned to factory specifications.