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Portal Axle Evolution: Lift Kit and Lower Gearing All Wrapped Into One

Posted in How To: Suspension Brakes on March 12, 2018
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Several years ago 4x4 enthusiast interest in portal axles had been piqued, and rightly so. No other modification offers the same increase in ground clearance, lift, and the low gearing needed for bigger tires all wrapped up into one convenient component. Early adopters made use of aged existing parts, and some even developed complete portal assemblies and knuckles, but the limitations ultimately dampened portal axle enthusiasm. Overall strength, packaging, available wheel lug patterns, steering scrub radius, and parts availability were some of the portal problems that needed to be overcome.

Portal axles are not new to 74Weld. The company was one of the early adopters that made use of stock Unimog 404 portal gears and loaded them into custom-machined billet aluminum boxes and steering knuckles. Today, 74Weld has pushed the envelope with the development and production of its second-generation portal boxes, gears, and hubs. The only parts in the gen-two boxes that remain the same as the aged Unimog 404 axles are the bearings and seals. Everything else has been redesigned, improved on, and made out of newer and stronger materials. The result is a portal axle box that provides 4.25 inches of lift, 1.55:1 ratio gearing, and enough ground clearance under a Ford 9-inch on 40-inch tires to drive over a 5-gallon paint bucket. Lots of options and different backing plates and knuckles are available to adapt the 74Weld portal boxes to solid axles or independent suspension applications. The company is also in the process of developing direct bolt-on portal boxes for Jeep JK and JL Wranglers. Keep an eye out for more info on these when they become available.

The factory Unimog 404 portal boxes (left) are made from cast iron and are known to crack around the bottom circumference in abusive conditions. The 74Weld portal boxes (right) are machined out of 6061 billet aluminum. Normally, the use of aluminum would result in some weight savings. However, the 74Weld portal boxes have been significantly beefed up with more material in critical areas, so they weigh the same as the factory cast-iron part but are much stronger.
The factory Unimog 404 portal box (left) and The 74Weld portal box (right).
The original Unimog portal gears (left) are 1.75 inches wide and have a reduction ratio of 2.19:1, which can make ring-and-pinion gear selection for higher speeds very limited. The 74Weld portal gears (right) are 2 inches wide with a more useable 1.55:1 reduction ratio. Unlike the original helical-cut Unimog gears, which are right and left side–specific, the straight-cut 74Weld gears can be used on either side of the axle. The straight-cut gears also allow for much easier assembly, have more tooth contact than stock, and are good for up to 1,000 hp. A 40-spline portal pinion gear is available for extreme heavy-duty and race applications.
On steering axle and independent suspension applications the 74Weld portal boxes are available with either a CV joint or a Dana 60–sized yoke machined from 4340 chromoly. The U-jointed stubs are designed and clearanced to turn to 50 degrees. The company says 300M yokes are available, but not needed because the gear reduction in the portal box reduces steering U-joint, axleshaft, ring-and-pinion, driveshaft, transfer case, and transmission stress by 55 percent. This allows you to use smaller, lighter, and less expensive drivetrain components upstream from the portal boxes.
The 74Weld portal box features a two-gear design. This requires the axlehousing to be built with a flipped over differential so the tires drive the correct direction. However, the bolt-on Jeep JK and JL Wrangler portal boxes will have a four-gear design to make use of the factory axlehousings.
The portal boxes can be adapted to a solid axle with either a machined billet 7075 aluminum knuckle (left) or with a much less expensive 4130 chromoly TIG-welded knuckle (not shown). For non-steering applications, a weld-on housing flange (upper right) and a matching aluminum portal box backing plate (lower right) are available.
Factory Unimog hubs (left) are made of steel and have a nearly unusable 6-on-205mm lug pattern. They have 1/2-inch-thick flanges that can bend under load. The 74Weld gen-one hubs (center) are machined from 6061 aluminum. The flange thickness has been increased to 3/4-inch. A built-in rotor hat lip increases rigidity and allows for the use of a 14-inch-diameter brake rotor and six-piston caliper. Gen-two hubs (right) utilize an adapter to attach the 14-inch rotor.
Rather than splines, you’ll find hardened alloy pins that drive the gen-two 74Weld wheel hubs. These hubs feature a 6-on-6.5 bolt pattern and 5/8-inch heavy-duty wheel studs to make use of relatively inexpensive used Trophy Truck wheels, but the hubs are available in almost any lug pattern, including the popular 8-on-6.5 bolt circle.
In place of the huge, clunky, and heavy steel factory Unimog hub bolt, 74Weld designed and machined a locking hub bolt mechanism for the gen-two hubs. A trick anodized billet aluminum cap covers the assembly and protects it from the elements.
There is a lot of attention to detail that goes into the 74Weld portal box assemblies. The billet aluminum knuckles receive pressed-in, heat-treated, hardened seats to keep the steering hardware from marring the assembly.
Tubeworks partnered up with 74Weld and manufactures the plate-style axlehousings for the portal knuckles. Each housing features massive 4-inch-diameter, 0.250-inch-wall chromoly tubes and allows for a Ford 9- or 10-inch centersection. Complete turnkey, ready-to-run portal axle assemblies with brakes are available from 74Weld.
Mating the 74Weld portal boxes to the Tubeworks housing allows for wheels with up to 7 inches of backspacing, substantially decreasing the scrub radius normally associated with portal axles. The 4.25-inch drop of the portal boxes provides massive amounts of ground clearance under the differential. Each knuckle is attached with double-shear mounts that house 1-inch uniballs, so no shims or adjustments are needed during assembly.
One of the many 74Weld portal box mounting options include heat-treated chromoly independent suspension uprights (knuckles). This set of portal boxes was integrated into an Ultra4 race car with long-travel four-wheel independent suspension.



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