The leaf spring suspension was the first to be used because of its simplicity and robustness. Usually linked to a rigid axle, the springs consist of several spring steel leaves mounted one above the other and secured by means of riveted collars. The top blade, or the larger master blade, has anchor points at each end. The length of the other blades decreases. The axle attachment point is in the middle of the spring, which has a semi-elliptical shape. The suspension by two rigid axles mounted on semi-elliptical leaf springs practically saw the light of day with the automobile itself, at the end of the XlXth century, to end its career some fifty years later.
Before World War I, cars did not have shock absorbers. The weight of the vehicle compensated to some extent for the relaxing movement of the springs. The first shock absorbers were friction. The most sophisticated were adjustable in hardness from the dashboard. Hydraulic shock absorbers with casings and levers, invented by Houdaille, then appeared in the early 1930s. They constituted a clear advance prior to the appearance of telescopic shock absorbers.
The rigid axle
If the rigid axle system! leaf springs have been used for so long, it is mainly because of its great robustness (the roads of the time were far from being worth those we have today) and of an obvious simplicity of manufacture resulting in a modest cost price.
Its main drawback is the high weight of the unsprung masses, which is detrimental to good road holding. The slightest shock recorded by one of the wheels of the same axle is immediately transmitted to the opposite wheel due to the rigidity of the axle; if it is a front wheel, the impact will be felt at the steering wheel by the driver. It is this set of defects inherent in this type of suspension that has led manufacturers to turn to other solutions.
By the 1950s, independent front wheels began to become widespread, with leaf springs only being retained for the rear axle which remained rigid. On some cars, however, a transversely mounted leaf spring was used to provide independent front suspension (Ford Panhard), with the spring also acting as wishbones.
Replacing the leaf springs
Despite its great strength, a leaf spring can end up sagging and gradually losing its resilience. One or more blades can break under a sudden shock, or under the effect of very strong corrosion. On this subject, it is interesting to note that the manufacturers of high-end cars mounted laced leather sleeves fitted with grease nipples around their leaf springs, until the late 1950s. These sleeves, stuffed with grease, prevent the spring from rusting and thus ensure a longer service life. We notice that a leaf spring is tired or broken when taking the heights of the car’s shell from the ground. If they are significantly lower than those indicated by the manufacturer, remove the wheels after mounting the car on jack stands using a floor jack: you will then have the leaf springs under your eyes and you will be able to see if one or more blades are broken. If so, they must be replaced. You can click here to find the kind of replacement options that there are.
Although out of fashion, this type of suspension still equips a few cars: the Japanese in particular, but also the small Fiat Panda. The rigid rear axle of this popular automobile is carried by single leaf springs, sufficient for the little weight they have to carry.