Up until the 1970s, leaf springs were a common feature on almost all vehicles. Since then, most passenger vehicles have switched over to coil spring suspensions. Yet leaf springs continue to be used on most semis and other heavy-duty commercial trucks. For that reason, anyone who regularly operates such vehicles should possess at least a basic understanding of leaf springs.
The more you understand leaf springs, the better you will be able to avoid suspension-related problems. If you own or operate a semi truck and would like to improve your knowledge of leaf springs, read on. This article will offer a useful introduction to this widely used feature of truck suspensions.
Leaf springs have a long history of use - one that goes way back before the advent of automobiles. Leaf springs were first used as a form of suspension on English carriages in the 1750s. For this reason, leaf springs are still sometimes referred to as cart springs. Leaf springs may also go by the more technical name of semi-elliptical springs.
A leaf spring consists of multiple metal strips - aka leaves - stacked on top of one another. Metal wires loosely bind the leaves together while allowing them to still slide against each other as they bend. Most leaf springs have a preformed arch that helps them to absorb and diffuse structural stress.
Like all suspension systems, leaf springs have two main goals. The first involves supporting the weight of the vehicle in a responsive, non-rigid way. The second goal involves absorbing the impact generated by imperfections in the roadway. These imperfections may include such things as potholes and bumps.
Leaf Versus Coil
As noted above, almost all passenger cars being manufactured today contain coil springs. This stems from the fact that coil springs allow for a greater range of suspension movement, which in turn allows the springs to better absorb shocks. Coil springs also permit cars a wider range of motion, making it easier for vehicles to negotiate tight turns.
With these advantages in mind, many people wonder why leaf springs continue to be used at all on semi trucks. Several good reasons exist for this. The first has to do with the relative load-bearing capacities of the two types of springs. Simply put, leaf springs can handle much heavier loads than a coil spring.
Coil springs simply don't have the strength or stability that a heavy-duty truck needs. Coil springs also tend to carry a much higher price tag. Even if a truck were equipped with coil springs, the cost of replacing them at the end of their serviceable life would be prohibitively high. The simplicity of a leaf spring helps to make them a more affordable option.
Leaf Spring Wear
Like all suspension springs, leaf springs wear out as time goes on. As noted above, leaf springs are manufactured to have a slight upward-pointing arch. Over years of service, this arch will sag downward. The lower it gets, the less effective the leaf spring will be at absorbing the bumps and shocks of driving.
The good news here is that sagging leaf springs don't have to be scrapped completely. Experienced mechanics can restore the ideal shape of a leaf spring through the process known as re-arching. Re-arching may be accomplished in one of two ways. The first, known as cold re-arching, involves the use of a hydraulic press to bend the leaves back into the correct shape.
The second method, known as hot re-arching, utilizes high temperatures to accomplish the shaping process. Both methods require that the leaf spring be taken apart into its constituent leaves. In either case, rearching represents a great way to extend the service life of a leaf spring.
For more information on getting the most from your truck's suspension, call the leaf spring experts at Odessa Spring Brake & Axle, Inc.