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Driveline Tech Tips

AXLES
You might think that all axles are essentially the same in material, design and manufacturing ˜but you'd be quite wrong. There are actually important differences in the materials used, how they are heat treated, the machining processes employed and even how the axle order is taken. And these differences separate axles capable of providing years of reliable service under the most demanding of conditions to those likely to cause driveline failure. The question begs asking, “Why do some axles cost more than others?” The obvious answer is for the racer to compare them and make note of the differences.

There are essentially two “classes” of axles; those made from a high grade steel alloy and heat treated throughout, and those made from lesser materials and induction hardened. And between the two there are other key differences, depending on the manufacturer.

One way that manufacturers can cut corners is to gang-run axles with the shaft diameter the same as the spline needed. When an order comes in, they simply chop the end off the generic axle to the desired length, typically cut about 4" of spline and ship it. While this sounds like a good way to save money, there are several serious compromises taking place. The biggest problem if axle lengths are not calculated and machined specifically for the application, as they are at Mark Williams Enterprises, is that it is not possible to build them with the proper spline length and incorporate the needed under cut. The problem with axles built without an undercut (smaller than the major spline diameter) is that the torque applied to the axle is concentrated in the splined area resulting first in a twisted spline and then eventually a total failure. Optimized axle lengths will improve torsional ductility and prevent the axle from taking a permanent set.

Spline count also plays an important role in axle durability, since the pitch of most common axle splines is the same, there is a direct correlation between the number of splines and the diameter of an axle. More splines equate to larger diameter axles, with 40 splines being the maximum. For lower horsepower, lighter vehicles 35 splines are adequate. For the record, 40-spline axles are 1.708" in diameter and 35-spline axles are 1.500" diameter. You should also know that all splines are not the same and spools/differentials/axles with similar counts may not be 100% compatible. Mark Williams Enterprises utilizes what's known as a true involute spline design, which has a slight crown, and 45-degree pressure angle. An OEM Dana has a 30-degree pressure angle. So even though both have 35 splines, they are not interchangeable. Some lesser quality axles have splines that are cut individually making it impossible to control the tooth profile and concentricity. All splines at Mark Williams are cut on a machine called a hob, which is the only way to create the true involute spline profile.

Last but certainly not least is the heat treating process. It is important to note that, Mark Williams Enterprises is the only axle manufacturer to perform all heat-treating (Austempering and induction hardening) in-house to assure quality control. M-W's popular Hi-Torque axles are made from a nickel-chromium-molybdenum alloy and heat treated using the Austempering process for superior strength and ductility.

For the racer who desires the strongest possible axle at the lightest possible weight, M-W offers its “Ultimate Hi-Torque” axles utilizing 300M material, lightened flanges and a 1" gun-drilled bore thru the entire shaft.

Mark Williams Enterprises also offers an economical street/strip axle known as Masterline. Masterline axles are also built to customers specs but utilize material and heat treating best suited for street/strip applications.

For more info on Hi-Torque or Masterline axles or for assistance in selecting the optimum axle/spool combination for any application racers can speak with the most knowledgeable tech staff in the industry at 866- 508-3374 or visit www.markwilliams.com.