When Strength Counts
Have you ever tried to sit down with a representative from an axleshaft manufacturer and talk steel? We suggest you bring a notebook, pocket recorder, a sandwich, and an open mind. Not only do many opinions vary in the land of steel, but often you will run into engineering minds that will slam more information onto your noggin than you ever thought possible.
For most of us, when the time comes to replace a broken axleshaft, we simply hit the forums, search for what others have done, and follow suit. Then, the age-old saying, “If your friend jumps off a bridge, would you?” comes to mind. So, we distill some of the knowledge a few experts gave us to help you the next time your axleshaft needs replacing.
First, what is an axleshaft and what does it do? An axleshaft is a central shaft that is used to turn a set of wheels. These axles transmit torque to the wheels and maintain the position of the wheels relative to each other and the vehicle body. The easiest way to put it is, power is made in the engine, sent through the transmission, pushed through the driveline, into the gear cluster, and out to the axles.
The two most common reasons axleshafts break are due to too much load from big engines and oversized tires. Both cause huge amounts of stress, applying it all through the axleshafts.
For all things load bearing, strength is the first thing that comes to mind. More specifically, how strong is the material being used to create the axle, does the size and profile of the shaft make a difference, and do the number and shape of the splines count.
Steel is the best choice for making axleshafts because it is strong, very stiff, and is elastic in nature. You can heat treat steel in many different ways, including induction hardening and through hardening. The process which aftermarket axleshaft companies harden the steel is what sets them apart from the typical OEM axles, which cannot be through hardened.
To save on cost, OEMs will use SAE 1055 or 1541 steel, which work fine for most of us, but the extreme wheelers among us that overly modify our toys require a little more strength, such as SAE 4340 or 300M steel.
Let’s use an example all of us can understand: You are out wheeling with your buddies and get stuck trying to tackle a huge boulder in your way. Your tires are wedged against the rocks and you slam your gas pedal to the floor, hoping that power will overcome your lack of driving skills. This is the No. 1 place 4x4 guys break axleshafts. This is where the type of steel your axleshafts are made from comes into play.
All axles, given the same size and profile shape, will twist exactly the same amount under the same load. However, an axle made from 1030 carbon steel will have exceeded its maximum strength and will most likely break. Your stock OEM 1541 axles may not have passed their maximum strength point, but will most likely never fully return to their original shape. The far stronger 4340 axle has much higher yield strength and will not have reached its maximum strength point, which will allow it to return to its original size and shape allowing you to continue on the trail.