There are several advantages to portal axles, where a geared hub is placed outboard on the axle assembly. More ground clearance is the most obvious advantage, but adding gearing at the end of the drivetrain reduces the torque on upstream components, allowing them to be smaller and lighter. If you have been following our ongoing Tracker project you will likely recognize that “smaller and lighter” is a mantra for Jesse Haines. Traditionally people have tried to utilize complete portal axles from Unimogs, or add portal outers to existing axlehousings, but the packaging can be difficult, particularly with the long pinion found on Unimog axles.
“Jesse Haines had an entirely different approach”
Haines, however, came up with an entirely different approach: Hummer portal boxes. Originally used on the independent suspension found under military HMMWV and civilian Hummer H1s, these portal boxes use two huge, straight-cut gears and inboard brakes. As a result, they change the direction of rotation of the drivetrain, but they are very strong and compact as well. Haines is not marketing these as bolt-on parts; he is focused on purpose-built rockcrawlers who are willing to build a tube chassis around these axles and the associated drivetrain.
As military HMMWVs are being decommissioned, parts become more available. Jesse Haines buys the knuckles in bulk and then disassembles, cleans, and inspects all components before giving them a new lease on life.
The inner knuckle is a fabricated piece with an offset cup to fit the end of a 3 1/2-inch axletube. Haines has the parts laser cut by Lasernut out of 1/4-inch-thick steel and fully welds the pieces together to box in each inner knuckle.
Instead of a typical ball joint or traditional kingpin, Haines uses a high-strength bronze bushing with a 7/8-inch through-bolt for the upper and lower pivot points. This systems is designed for maximum strength in low-speed rockcrawling and trail-only applications at the expense of the longevity that would be required for a daily driver.
The factory Hummer steering arms are tossed in favor of a 1-inch-thick, laser-cut plate fitted with a grease cap. Note how the steering location is moved up for increased ground clearance. Haines has designed the steering to utilize a double-ended ram for fully hydraulic steering.
Helical-cut gears are quiet, but that was low on the priority list for the military when they were spec’ing out the HMMWV. Straight-cut gears, like those used in the Hummer, are incredibly strong. These portal boxes offer a gear reduction of 1.92:1 through the two gears.
The stub shaft exiting the portal box is after the gear reduction, so a 2-inch, 32 spline stub is used to withstand the huge torque load. The bearings are off-the-shelf parts that are easy to find at any parts store in the country.
RCV 300M CV axles are used to connect the portal axle to the inner axleshaft. The 31-spline inner axles (factory Ford size) are plenty strong since they only experience half the torque load found in traditional axles.
Hummers use independent suspension with inboard brakes, but that would not work for a solid axle configuration. Haines uses outboard brakes with lightweight, nonvented cross-drilled rotors from Trail-Gear. He bolts them to the factory stub shaft, which is machined to change the bolt pattern from (in this case) 8-on-6 1/2 to 6-on-5 1/2. Other bolt patterns are available.
Haines uses superlight Wilwood drag racing calipers, but larger six-piston calipers are an option. This photo is of an early caliper mount, they now have mounting brackets on both sides of the caliper to resist any bending due to the added stresses of the portal boxes.
Haines welds his fabricated knuckles on to Trail-Gear Rock Assault fabricated axlehousings. The housings come bare and he cuts the tubes to the appropriate length for the required differential placement and axle width.
Yukon aluminum third members from Randy’s Ring & Pinion were chosen for their light weight and excellent strength. The case has increased rib thickness for rigidity and uses forged 6160 aluminum bearing caps. The third members also use a load bolt to prevent ring gear deflection under load.
Haines set up his own gears using a Yukon ring-and-pinion and Yukon install kit with Timken bearings. With the 1.8:1 reduction at the portal boxes, he runs a 5.13 gear ratio in the third members for a total of 9.84:1 in his competition rock buggy. Yukon offers inch gear ratios from 3.0 all the way to 5.13 for the 9-inch third member.
Yukon Zip Lockers were chosen for the ability to turn off and operate as open differentials. While this may seem like it would only be a benefit on the pavement, unlocking the different allows for increased maneuverability in competition, even with steering axles front and rear.
The steering arm mounting is tied into the plate on the inside of the portal box. Haines uses 3-inch doubled-ended hydraulic rams on his personal buggy, but the steering could be set up with a traditional tie rod as well. Rear, non-steering axles are also available.
The assembled third member uses an aluminum Yukon Daytona pinion support that accepts a larger inner pinion bearing to reduce gear deflection under load. With the torque multiplication downstream, Haines has been running 1350 drivelines from JE Reel without issue.
Like ground clearance, steering angle is another issue that is critical when dodging cones in rockcrawling competition. The added maneuverability provided by a tight turning radius is also a benefit on technical trails though as well. Jesse Haines’ portal axles turn 45 degrees. For comparison, a typical Dana 60 turns 32 degrees.
Haines is one of the first people to be running the new 42-inch tall Maxxis Trepador. With the portal axles on his buggy, Prickle, he has a whopping19 inches clearance under the differential and 23 inches of ground clearance under the axle tubes. The axletubes are actually higher than the belly on his buggy.