Technical Articles Relating To Off-Road Vehicle Development

Not Signed in ( Sign In )

Ultimate Toyota-Based Axles: Part 2

Published by Trails Less Traveled on December 29th, 2004


Animation of Axle Being MadeSuperior Axle & Gear is well known as a manufacturer of top-quality aftermarket axle-shafts and gear-sets. Recently, we had an opportunity to tour the Superior facility in Los Angeles with Mike Denton Jr., who talked with us about what goes into designing an axle-shaft and then walked us through the steps involved in the manufacturing process. That’s convenient since axle-shafts are the subject of this installment in our ‘Ultimate Toyota-Based Rear Axle’ build-up.

All Toyota 8” and Non-TRD Tacoma/T-100/Tundra axles use 1.3” (major) diameter, 45° 30-spline axle-shafts. We are working with these stock dimensions to ensure that our axle-shafts remain compatible with stock aftermarket carriers/lockers. It’s entirely possible to broach-out the side-gears in a Toyota ARB locker to accept a larger diameter axle, but Mike pointed out that a pair of his 30-spline axles would probably exceed the ultimate strength of something in the third member (meaning that the ring & pinion, carrier or drive flanges would fail before the axle-shafts).

Superior custom-made a set of 4340 full-floating axle-shafts for our Front Range Off-Road axle-housing and full-floating conversion kit. Because our axles use splines on both ends (at the differential and the drive-flange), we had a very straightforward profile (changes in axle diameter). Each axle has one seal-surface at the wheel-hub, which features smooth radii to reduce stress risers. Some people are making a big deal about rolled splines, but the truth is that properly hobbed splines (especially if cut before heat-treating) will offer comparable strength in most real-world applications. Very few custom axles actually feature rolled splines because of the tooling, additional setup time and expense associated with this step. It’s really only practical for production runs.

The ultimate strength of an axle is a result of proper design, material selection and the manufacturing process. There have been some fantastic technical articles related to axle technology and material selection published recently. We would encourage readers to check out the following articles for more information about materials and axleshaft design/strength.

Steel and Material Strength by Billavista on Pirate4×4.Com

Axle Shaft Technology by Billavista on Pirate4×4.Com

‘Axles 101’, Four Wheeler Magazine (January ’05, Author: Jim Allen)


Some of Superior ProductsThe countertops of the Superior offices are covered with all types of product samples.
Examining the design limitations of stock components is the first step towards improving (strengthening) any axle-shaft.

Destructive Testing SampleBroken parts make better parts. How’s that? Broken parts reveal flaws that can be addressed with improvements in design, materials and the manufacturing process. Mike explained to us how the nature of this failure indicates that there might not have been adequate spline-engagement because the break occurred halfway down the splined area of the shaft and the splines are straight on the broken axle-stub. Cracks running lengthwise down the shaft from several of the splines also indicate that the spline-root was an area of concentrated stress.

Strength Analysis SamplesThese samples parts are being analyzed to verify that proper penetration and Rockwell hardness has been achieved during the heat-treating process. Heat-treating is just as important as material selection or an axle’s profile design and must be performed by someone that is familiar with the material and desired characteristics. All of Superior’s heat-treating is performed in-house.

Mike Denton Jr Guiding TourRaw Steel BilletsHere you can see the various lengths of raw billets they keep on hand. Superior processes over 300,000 lbs of steel to make more than 10,000 axle-shafts each month. In addition to manufacturing their own line of performance products and private-label aftermarket products, Foote Axle (Superior’s parent company) also produces axle-shafts for OEM automotive and commercial/industrial applications.

Billets being cut to lengthBlueprints of Axle SpecsThe appropriate material is first cut to length in one of these huge hydraulic shears. Then the cut material is organized into manageable batches and processed according to the instructions/build-sheet that accompanies every batch of axles.

Heating Shafts to form FlangesTransferring Red-Hot Shaft to Press For ShapingBecause of California’s ‘Energy Crisis’, the workday at Superior begins before 3am in order to avoid the peak electricity rate hours. These guys handle themselves casually as they work with the heated axles, but they move with amazing efficiency to ensure that the material stays hot and workable. The bar-stock for semi-floating axle-shafts is cut extra-long so that one end can be forged into the axle-flange.

Red-Hot Axle Placed in PressFlange Being PRessedFlange Shape FinishedThe bar-stock is forged into a semi-floating axle blank at red-hot temperatures and under extreme pressure.

Shaft Being Prepped for Final Hot-ShapingRe-Heated FlangesThe wheel flange is re-heated in the furnace between forgings. Careful control over the heating and cooling of the axles during manufacturing is a major part of their resulting strength.

Large Forging MachineThe final forging of the wheel flanges takes place at near room temperature. This is impressive to watch, but it made our heads ring. The hammering motion of this machine is so powerful that it breaks at least one of those huge Oak beams each month.

First Stage of MachiningCompleted forgings are then CNC machined to final tolerances, except for bearing & seal surfaces, which are machined after heat-treating.

CNC Lathe Removing MaterialAxle Finished in LatheThe tooling is incredible. These cutters are capable of removing up to 1/8” of 4340 in a single pass! Superior invests in the equipment and processes (like CNC lathes/mills & heat-treating equipment) that allow them to manufacture premium quality components in the US instead of manufacturing inexpensive parts overseas.

In-House ToolingSuperior also manufactures most of the tooling to keep their heavy equipment running in-house. Parts for many of their machines are so specialized that they can’t afford the downtime that it would take to order replacement parts from a manufacturer or tool-smith.

CNC Mill Drilling Bolt-Pattern onto FlangeFinished Drilled FlangesAxle flanges are drilled for wheel-studs in this specialized CNC mill.

Manually Removing Run-OutClose-UpStraightening the axles to eliminate run-out is impressive because it’s still all done free-hand. Francisco “Poncho” Garcia has been working at Superior straightening axles for many years. Each axle is rotated by hand, moving up and down the length of the shaft to measure the run-out and make any necessary adjustments.

Spline Rolling DiesSpline Rolling DiesThese images illustrate the variety of dies used to roll axle splines. Different dies are used according to the pressure angle of the splines and diametric pitch (the number of splines relative to the axle diameter).

Spline Rolling machineThis is the spline-rolling machine that is used to literally roll the axle over the dies. Rolled splines are so strong because no material is removed (the splines are essentially cold-forged). Unfortunately, we didn’t get an opportunity to check out the hobbing process.

Top View OF Shaft Being Through-HardenedShafts Ready for Last Stage of ManufacturingThese images show how alloy axles are through-hardened with an electro-magnetic charge, which heats an entire axle evenly in a matter of seconds, before it is quenched. The result is an axle that is heat-treated evenly all the way through the part, as opposed to plain carbon-steel axles which can only be induction-hardened. Induction-hardening only penetrates the surface of an axle, which is great for a ring & pinion set but is not ideal for heat-treating axles.

Through Hardening MachineFinished Axle Clode-UpAxles go through a final round of machining after heat-treating to ensure that the bearing and seal surfaces maintain accurate tolerances. Axle dimensions are then checked against the build-sheet again to ensure all the parts are 100% accurate.

Finished Batch of Shafts Ready to ShipThis batch of axles is ready to be packaged and shipped. Many of these axles are being delivered to other aftermarket manufacturers/vendors to sell as part of custom-built axle assemblies. Next month we’ll take a look at the FROR axle-housing and full-floating conversion components.

This Article was originally published on January 2005

Links to other articles in the Ultimate Toyota-based Axle build-up:

Introduction to Gearing
Part 1: Gearing and Locker Selection
Part 3: Diamond Axlehousing & Full-Floater Conversion


Have A Comment Or Question About This Article?

We would love to hear any questions or comments you have about this article. Please take a moment to fill out our feedback form.