The problem wasn’t just finding an 8-lug rear axle. This truck needed to stay on the factory 180 mm bolt pattern, work with a custom chassis, and leave room for the bracketry that comes with a Watt’s-link setup. A conventional flanged axle wasn’t the answer because the flange size wouldn’t support that bolt circle, and that style of axle also has to carry both bending load from the wheel and torsional load from the drivetrain. The fix is a custom full-floating rear axle built around a 9-inch housing. In a floater setup, the spindle and hub carry the wheel load through tapered bearings, so the housing takes the bending load and the axle shaft mainly transmits torque. That’s a stronger, safer way to handle big tire load and diesel power. To make it all work, the spindle is being built as a hybrid: factory-style on the outside to retain the stock bolt pattern and brakes, and Strange-style on the inboard side so it can weld into the 9-inch housing like a race floater. Inside, the plan uses a 35-spline axle with an Eaton Truetrac differential. That gives a broad range of differential options in the 9-inch platform, along with quiet operation and solid traction without clutch packs to wear out. The result is an 8-lug rear end that keeps the truck’s heavy-duty identity while solving the packaging and strength problems a standard axle couldn’t touch.
The episode centers on an unusual hot-rod requirement: building an eight-lug axle package for a custom chassis being planned with Roadster Shop. Because eight-lug hardware is uncommon in the hot-rod world, the team travels to Strange Engineering in Morton Grove, Illinois, to work through the rear-axle challenges before moving on to the front suspension.
Strange Engineering has deep roots in racing hardware. Founder Bob Stange began more than 60 years ago building drag-race parts for Chicago racers out of his mother's two-car garage. A printing error in the 1960s changed the company name from Stange Engineering to Strange Engineering, and the name remained. Today the company operates from a 120,000-square-foot manufacturing facility led by Bob's son Jeff, producing high-performance axles, housings, floater kits, differentials, ring-and-pinion gear sets, driveshafts, suspension and brake systems, steering components, and related racing parts.
The main engineering obstacle is the factory 180 mm bolt pattern. Strange explained that its traditional axle forgings use a flange that is not large enough to support a bolt circle that big. In a conventional flanged axle arrangement, the wheel bolts directly to the axle flange, so the flange size becomes the limiting factor.
That constraint forced the project away from a standard flanged axle and toward a full-floater design. Rather than trying to stretch a conventional axle beyond its intended geometry, Strange proposed adapting one of its proven racing floater concepts to a custom housing that could still work with the factory-style eight-lug hardware.
Strange demonstrated a floater spindle used in Pro Mod applications, where cars can produce 3,000 to 4,000 horsepower. The idea was to adapt that level of hardware quality to this custom rear housing. The company emphasized that the floater approach is especially attractive when large tires and high torque are involved.
With a flanged axle, wheel loads create bending forces at the axle flange. Those bending loads act on the same shaft that is also transmitting torsional load from the engine, which can become a problem in a high-power diesel application. In a floater setup, the spindle is fixed into the axle tube, so the housing absorbs the bending loads. The axle shaft then primarily sees torsional load instead of both bending and twist.
Strange also pointed out the safety benefit. In a floater arrangement, the wheel is supported by the hub and spindle assembly on the outside of the housing. If an axle-related failure occurs, the outer assembly remains retained. By contrast, if a conventional axle flange fails, there is a risk of losing the wheel, which could be catastrophic.
The company walked through the difference between the two architectures. In a traditional housing, a bearing is installed on the axle, the axle sits in the housing, and the wheel bolts directly to the axle flange. In the floater version, a spindle supports a drive hub that slips over it. That hub is the part the wheel bolts to.
The hub rides on tapered bearings, and a drive plate on the outside connects the hub assembly to the axle shaft. In this arrangement, the spindle and housing carry the bending load while the axle shaft transmits torque. That separation of duties is the core reason a floater setup is preferred for severe service and high horsepower.
Because the build is moving to a Ford 9-inch-style housing instead of the factory differential, the spline arrangement changes on the inboard side. Strange specified a 35-spline axle interface for the 9-inch platform. The company noted that the 9-inch offers many differential choices, including Eaton Truetrac and Eaton locker options, allowing the final selection to be matched to horsepower and intended use.
For this project, Strange recommended the Eaton Truetrac. The 35-spline configuration was described as capable of handling a tremendous amount of horsepower, making it a practical fit for a diesel-powered custom vehicle while still taking advantage of the broad aftermarket support available for the 9-inch platform.
Jeff from Strange Engineering then outlined the custom solution. Since a standard flanged axle could not accommodate the large bolt circle, the company proposed using a full-floating hub and spindle assembly with a custom spindle that would preserve the factory bolt pattern and brake compatibility while fitting a narrowed 9-inch housing.
The plan was to capture the dimensional data from the factory spindle and create a hybrid spindle. The outboard side would mimic the factory geometry so the build could retain the factory-style hub and bolt circle for the wheels and brakes. The inboard side would use Strange's own floater-spindle construction so it could engage properly with the housing tube in the same manner as the company's drag-racing floater systems.
Jeff said the spindle would be made from chromoly for weldability, strength, and toughness. Structurally, he described the concept as very similar to the rear axles Strange builds for roughly 2,000-horsepower applications. The difference here is that the outboard side must interface with factory components, while the inboard side remains an aftermarket 9-inch racing-style design.
The shop tour then shifted to manufacturing. At the spline machine, Strange explained that it performs NC hobbing and starts with a high-toughness axle forging. One of the company's key process choices is to complete machining operations before heat treatment. According to Strange, this helps maintain tighter tolerances and contributes to a better finished product.
From a forged blank to a finished axle, the part moves through roughly five or six stations. The process begins with initial turning, which is essentially a rough cut that prepares the axle for spline cutting while intentionally leaving extra material on the bearing journals and axle flange. That extra stock allows the company to true those surfaces during final machining.
After spline cutting, the bolt pattern is added. Once the machining steps are complete, the axles go out for heat treatment. Strange described the resulting through-hardening as making the axle very strong in torsion. When the parts return from heat treat, the bearing journals and axle flanges receive their finish turning operations, after which the axles are ready for assembly and use.
In the assembly area, Strange showed how a 9-inch center section is built from a range of available components. Customers can choose among different positraction units, gear ratios, case upgrades, pinion yokes, and other options depending on the intended application. Once the specification is set, the center section is assembled accordingly.
To illustrate the broader range of hardware the company builds, Strange also displayed a Top Fuel ring-and-pinion set rated for more than 10,000 horsepower. That was far beyond the needs of this Duramax-based project, but it underscored the company's experience with extreme driveline loads. For the custom truck build, Strange said the 9-inch setup would be more than strong enough.
The tour also included a 10.5-inch assembly described as the predecessor to the 12.25-inch unit used in alcohol funny cars. Strange said this type of rear assembly handles 3,000 to 4,000 horsepower routinely. In race use, service life depends on conditions, but in an alcohol car a unit like that may see roughly 50 to 100 passes before replacement or teardown, often for preventive maintenance rather than outright failure.
Strange returned to the differential choice and explained why the Eaton Truetrac suited the project. Unlike clutch-style or cone-style limited-slip units, the Truetrac uses a helical-gear design and does not rely on clutches or springs that wear out over time.
In normal street driving, the helical differential engages and disengages smoothly and quietly. Under power, the internal gears wedge together to create true positraction action. Strange described it as an excellent all-around differential for street driving, drag racing, and road racing because it combines drivability with strong performance behavior.
When the unit was opened for inspection, the internal helical gear arrangement was visible, with five gears on the top and five on the bottom interacting to allow differential action while still biasing torque when needed. That combination of smooth operation, durability, and traction made it the preferred choice for the custom 35-spline 9-inch rear.
By the end of the visit, the rear-axle direction was clear. Strange Engineering would build a custom eight-lug rear based on a 9-inch housing, a chromoly hybrid floater spindle, factory-compatible outboard geometry, and a 35-spline axle with an Eaton Truetrac differential. The design preserves the factory 180 mm bolt pattern and brake compatibility while moving the load path to a stronger full-floating architecture better suited to large tires and diesel torque.
With the rear solution defined, the project's next challenge became the front end. The team still needed matching eight-lug front spindles, which set up the next stop: a visit to Kibbe Tech Off-Road.