Leaf Springs - Semi Trucks

What Is A Semi Truck Leaf Spring?

A semi truck suspension leaf spring is individual steel slates that are bolted together, arched and have the ability to flex. Leaf springs are located in-between the axle and the frame of a vehicle and provide the vehicle with carrying capacity, ride height, axle location and tire alignment. The leaf spring is also partially responsible for absorbing road shock and creating a smooth ride. Leaf springs can be found on all makes of big rigs including Hendrickson, Ford, International, Peterbilt, Kenworth and more.

How To Tell If Semi Truck Leaf Springs Are Worn

There are multiple signs to know if your semi truck leaf springs are worn. The most obvious is direct damage to the leaf spring. For example cracks in the spring, a broken spring, a crooked or a twisted spring. Another sign that a leaf spring may be worn is sagging. If the front or rear of the vehicle is leaning or sagging that may be a sign of spring failure. There are also other components in the leaf spring that can wear which can cause the spring to wear pre maturely. For instance the leaf spring bushings, the mounting bolt can wear through the bushing then into the spring eye causing damage. There are also the spring tip inserts which are on the end of each individual leaf. If those wear that can cause the spring on top of another to wear into the one below. So it is just as important to inspect your leaf springs annually along with the bushings and tip inserts.

What Causes Semi Truck Suspension Leaf Springs To Wear?

Here we will will go over a few different reasons why semi truck leaf springs wear. The most common reason leaf springs fail is overloading. Some people may overload their vehicle not knowing how much weight that they are hauling or how much weight their vehicle can carry safely. Overloading your leaf springs can cause them to fatigue prematurely flattening them or breaking them. Corrosion is another common cause of wear. Big rigs in harsh elements can begin to rust on the spring which will greatly decrease the life span of the spring. The last common way suspension leaf springs wear is age. Leaf springs can last for decades but eventually will give out. Expect a vehicle with 30-40 years or more of age to need leaf springs in the near future especially if towing and hauling was something that was frequently done.

What Is The Difference Between Heavy Duty And OEM Leaf Springs?

For some vehicles there are two options of semi truck leaf springs that you can use, original equipment (OEM) and heavy duty. First we will start with original equipment leaf springs. A OEM replacement leaf spring is going to be a exact replica of the leaf spring that was first installed on the vehicle from the manufacture. This replica will either come from the original manufacture (Hendrickson, Peterbilt, International) or a aftermarket leaf spring production company. This option is typically for people who don't want to increase the stiffness of the vehicle and don't do any type of frequent heavy hauling or towing. Heavy duty leaf springs on the other hand will have a increased carrying capacity than the OEM spring. This means a stronger spring but the down side is due to the increase in capacity the spring will be stiffer and the vehicle will ride rougher.

When Replacing Leaf Springs What Else Should I Replace?

If you are doing a semi truck leaf spring replacement there are connecting parts that we do recommend replacing at the same time.

  • Leaf Spring U-bolts - The U-bolts connect the leaf springs to the axle housing and as a rule of thumb should always be replaced if they are removed.
  • Leaf Spring Spring Eye And Frame Bushings - Eye bushings and frame bushings are the insulators so the mounting bolts do not rub directly into the frame or spring eye. We do not recommend reusing bushings due to the inexpensive cost of most bushings and short amount of time HB bushings take to install as well.
  • Leaf Spring Shackles - The shackle is the pivot point for the leaf spring allowing it to flatten. The shackle will have to be removed while replacing your leaf spring anyways so to save on time we recommend the shackle being replaced as well.

How To Measure A Semi Truck Leaf Spring

Below is a diagram of how to measure a leaf spring. You will need the eye to center bolt measurements (A and B) which must be taken along the surface of the leaf spring. The arch height (C) which is measured by drawing a line from the spring eye to spring eye or spring end then another from the top of the center bolt to the middle of the first line measured. Last is the leaf spring stack height (D) which is the measurement from the top of the leaf spring to the bottom of the spring. With those four measurements you should be able to match up the leaf spring properly.

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