What is a Leaf Spring ?
It is a narrow board-shaped spring which comprises part of the suspension. It is an important component which supports the vehicle body and becomes stronger when several layers are added, making them suitable for trucks, trailers and buses.
Leaf Springs Made by Nakano Spring Co., Ltd.
Our leaf springs are made from high quality, fully tempered spring steel, and manufactured in our own factory being strictly monitored from form working, assembly, coating up to final quality inspection. Visual inspection of each process is undertaken to maintain our high quality.
Consistent high quality and level of engineering built up over the years is behind our ability to supply many OEM products as well as manufacture various types of leaf springs.
A spring made up of several layers of leaf springs of different lengths. Basically, the thickness of each leaf is constant, but some leaves may be slightly thinner towards both ends (within 30mm from the edge) (short taper).
Usually called TLS. A leaf spring made of several layers of leaf, where the thickness of each individual leaf differs over its length. The weight is lighter and there is a gap between the leaves. There is hardly any difference in the length of the leaves, and the center and edges of each leaf is in the same position as the leaves above and below.
No.1 leaf has an eye with a bush inserted. From the top, it is called leaf No.1,2,3..
A form of spring mainly used in single rear axle type middle and small sized trucks. The lower, longer spring is called the main, and the upper shorter spring is called the sub (or helper or assist). Both main and sub leaves are called No.1,2,3… starting from the top leaf.
A form of spring mainly used in double rear axle type large trucks. It is sometimes called a reverse spring due to its being installed with the arch of the spring in the reverse of the usual direction, and the leaves are called No.1,2,3…starting from the bottom. While other springs are placed on each axle, this is installed in the center between the two rear axles.
There are two types of double rear axle vehicles, where both rear axles are drive shafts (double differential gear) and other only one rear axle is powered (single differential gear). For double differential gear vehicles, the center bolt is located at the center, but for single differential gear vehicles the center bolt is shifted to one side (spring shown here is for single differential gear type).
The know-how and experience which we have accumulated over the years making products for many kinds of vehicles and for various uses at our safe and reliable factory enables us to offer quality products which meets our customer’s high standards.
What kind of materials are leaf springs made from ?
It is made from a type of steel called Spring Steel. Spring steel differs slightly from pure iron as it contains about 0.5% of Carbon and trace amounts of other elements such as Manganese, Chromium and Silicon, and is called low-alloy steel.
What is the important factor in spring steel ?
If the steel material contains impurities such as Phosphorus or Sulphur or non-metallic items like brick particles, it means bad quality. Material which has not been properly tempered is also low quality. It is like sword steel which has not been properly forged by hammer. NSK uses only high quality material which have been fully tempered.
What other points are important regarding the material ?
Material with scratched surface or which have been exposed to high temperature for too long during the manufacturing process causing Carbon loss at the surface (decarbonization) also means low quality. Material which has been over-decarbonized will not harden when quenched and so cannot be made into high quality spring. NSK materials are visually inspected at every step of the production process to maintain high quality.
The leaf broke at the center bolt hole ?
If the U-bolt is properly tightened, the leaf spring between the U-bolt does not function as a spring. Which means pressure is not applied repeatedly in the area between the U-bolts. When the U-bolt becomes loose while running and load is applied between the U-bolts where it shouldn’t, and as the center bolt hole is the weakest point it breaks at that spot. This is not the fault of the leaf spring itself, and checking the U-bolt whether it is properly tightened should be done regularly. If the U-bolt does not tighten properly even when power is applied, it could be that the U-bolt has stretched. Bolts which have been properly heat treated should be used.
Should the whole assembly be replaced in case of leaf springs ?
Yes. Leaf springs last longer when whole assembly is replaced. Of course, when considering the cost you may want to replace only one leaf, but even in such case we recommend to replace at least three leaves, the one broken and those above and below it. The reason is these leaves may be scratched when the leaf between them is broken, which makes them weaker and prone to damage. Scratches increase surface fatigue considerably, so although assembly replacement may seem expensive, in the long run the total cost may not be so much.
Purchased just one leaf for replacement, but the camber doesn’t fit properly ?
When manufacturing the leaf spring at the factory, NSK makes sure the product is quality controlled with all measurements within the margins allowed in the drawing. Of course some margin is allowed, so those completed with minimum limit of allowance and those finished with maximum limit of allowance could end up with a small difference. This might cause a slight difference in camber. NSK is sensitive to such problems and does its best to avoid interchangeability problems before products are shipped out from the factory.