Axle Truss

Why truss an axle

An axle housing is a steel tube with a cast or fabricated center section, and under enough load it bends. Big tires add leverage, lockers and low gears add torque, and a hard landing can put the whole weight of the vehicle through one wheel. The result is tubes that bow upward at the ends, which puts the pinion out of alignment, chews axle seals and bearings, and in bad cases cracks the center section welds. A truss welded along the top of the housing adds a tall section that resists that bending. It also happens to be the right place to put new link, track bar and shock brackets, which is why so many trusses here are sold as swap kits with brackets built in.

Trusses, swap kits and brackets

• Plain truss: a 1/8 or 1/4 inch steel structure cut to the housing profile. Examples are the Artec APEX truss for the JL Rubicon Dana 44 front and the Trail Gear Rock Assault trusses for Toyota rear axles. These reinforce a stock or built axle that keeps its factory brackets.
• Swap kit: a truss with link, anti-sway bar, track bar and shock brackets attached, so a donor axle such as a JK Dana 44 or a Ford Dana 60 can be installed under a TJ or JK. Steering ram mounts are usually not included.
• Add-on brackets: upper link mounts and adjustable panhard mounts that bolt or weld to a specific truss, with multiple hole positions for tuning geometry. These are sold for one truss and one tube diameter.

Getting the fit right

Trusses are cut for one axle type and tube diameter. A Dana 44 has 3 1/8 inch tubes on a JK, a Dana 35 has 2.625 inch tubes, a Dana 60 commonly 3 or 3.5 inch, and Toyota housings have their own profile. Front and rear trusses differ because of the differential offset and the steering. Check the axle model, the tube diameter and whether the truss is for the high pinion or low pinion version. Dana 60 swaps also change the wheel bolt pattern to 8 lug and require new brakes and steering, which the kits do not include. Thickness matters too: 1/4 inch trusses are heavier and stiffer for one-ton builds, while a 1/8 inch APEX style truss adds rigidity to a stock JL axle with less weight.

Welding a truss without warping the housing

Welding puts a lot of heat into one side of the tube, and the tube pulls toward the weld as it cools. A truss welded in one long pass will bend the housing. Fixture the housing so the ends are held in alignment, or install the axle shafts and check that they turn freely as you go. Weld in short stitches, alternating ends and sides, and let the housing cool between passes. Many fabricators preheat cast center sections and use a nickel rod or a MIG process suited to cast iron where the truss meets a cast housing. Grind paint and scale to bare steel first. When the truss is done, check pinion alignment and axle shaft runout before putting the axle under weight.

If you have not welded structural steel on a vehicle before, this is a job for a fabrication shop. A poorly welded truss can crack at the welds, which is worse than no truss.

Other details

Trusses raise the top of the housing, so check clearance to the fuel tank, floor, exhaust and upper links at full bump; Artec notes a minimum 1.5 inch lift and extended bump stops for its JL truss. Trusses arrive bare and must be painted or coated after welding. Plan the link bracket positions with your lift and tire size in mind, since cutting a bracket off later is far harder than placing it right once.