Off-RoadWeb Homepage Off-Road
Facebook Click here to find out more!

Making Off Road Trailing Arms

The Hard Way And The Easy Way

By Kevin Blumer, Photography by Kevin Blumer
Custom Trailing Arms Trailing Arms

Trailing arms (AKA lower links) are one of the most important suspension system components on a long-travel linked rear suspension. Trailing arms must withstand forces from three sources: the terrain acting upon the wheels, the weight of the chassis, and the shocks' damping. If your trailing arms aren't strong enough they'll bend, or worse, break.

There are four main factors to consider when designing trailing arms: length, geometry, strength, and ground clearance. Bigger, longer trucks will best use bigger, longer trailing arms. Geometry refers to the lateral (or fore and aft) location of the shock mounts between the front and rear mounting points, and the vertical location of the shock mounts relative to the plane (or centerline) between the front and rear trailing arm mounts. As to strength, more is better, but there's a fine line between weight and strength. Too much strength is almost never a bad thing, but too much weight creates problems. Finally, trailing arms hang down pretty low, so they should be designed with as much ground clearance as possible.

There are three ways to get a set of trailing arms: the super-hard way, the hard way, and the easy way. The super-hard way is to design and fabricate your trailing arms completely from scratch. The hard way is to use pre-cut, pre-designed materials and do the welding and assembly yourself. The easy way is to buy your trailing arms pre-made.

We'll cover the hard way and the easy way in this story.

Custom Trailing Arms Parts And Hardware
You're looking at the benefits of our day and age. The old way would have involved paper templates and a bandsaw, which is still a viable, albeit time-consuming, way to fabricate parts. Computer design work and CNC laser cutting streamlined the process. Both 0.125-inch and 0.090-inch sheet thicknesses were used to make these parts. Any thermal cutting process (laser, plasma, oxy-acetylene torch) leaves behind a burned edge (or "scale") that should be removed for optimal weld quality. I sanded the scale away before starting to weld. These trailing arms are 60 inches long and designed to use with a 125-inch wheelbase.
Custom Trailing Arms Parts And Hardware
You're looking at the benefits of our day and age. The old way would have involved paper t

The Hard Way
This set of trailing arms was designed by my friend Dan Barcroft, who has also designed an online four-link calculator that can be used by anyone to design a complete four-link system. The four-link calculator will help you figure out the geometry of your four-link, but it will not design the individual parts and pieces. Dan designed the trailing arms seen here using Solidworks software, the results of which were sent to Elite Laser Cutting. Elite turned Dan's .dxf files into finely-cut pieces of 4130 Chromoly plate. The assembly and welding were done in a home garage by yours truly.

  • Custom Trailing Arms Parts
    These parts were used to build a jig for the arms. They'll be welded to a heavy steel backbone.
    Custom Trailing Arms Parts
    These parts were used to build a jig for the arms. They'll be welded to a heavy steel back
  • Custom Trailing Arms Assembling Arms
    Building the jig required temporarily assembling the arms. The individual parts have tabs and slots, making assembly instinctual. These trailing arms were designed to be used with standard-length shock rod ends. This meant that the top needed to be fairly flat, and the shock pocket couldn't be too deep.
    Custom Trailing Arms Assembling Arms
    Building the jig required temporarily assembling the arms. The individual parts have tabs
  • Custom Trailing Arms Surplus Rectangular Tubing
    Surplus rectangular tubing 2 inches by 6 inches with a 0.250-inch wall thickness was used to make the jig's backbone. Our local metal yard sells surplus odds and ends by the pound instead of by the foot, so it will cost you less if you find what you need in the surplus corner. Stubs of 1.5-inch round tubing were welded to the ends so that the jig could be rotated rotisserie-style for easier welding. The jig was supported by an extra-tall jackstand at one end and a bicycle workstand at the other.
    Custom Trailing Arms Surplus Rectangular Tubing
    Surplus rectangular tubing 2 inches by 6 inches with a 0.250-inch wall thickness was used
  • Custom Trailing Arms Center Tab
    Here's the center tab for the jig, which bolts into the shock mounts.
  • Custom Trailing Arms Spherical Bearings
    Spherical bearings (a.k.a. uniballs) will be used at each end of these trailing arms, but only the uniball's outer cup will be used during the fabrication stage. HM Engineering, who made the uniballs and cups, made a set of steel slugs to be inserted into the uniball cups during fabrication. I welded a tube into the slugs' center bores, and then the complete assembly was ready to bolt on.
    Custom Trailing Arms Spherical Bearings
    Spherical bearings (a.k.a. uniballs) will be used at each end of these trailing arms, but
  • Custom Trailing Arms Partially Assembled
    Here's the partially-assembled trailing arm in place with the jig tabs ready to weld to the jig's 2x6 steel backbone. After the jig was ready, the cutting scale was ground off of the trailing arm pieces, the pieces were assembled and set into the jig, and the welding finally commenced.
    Custom Trailing Arms Partially Assembled
    Here's the partially-assembled trailing arm in place with the jig tabs ready to weld to th
  • Custom Trailing Arms Welding Trailing Arms
    We've skipped way, way ahead here. Suffice it to say that when welding trailing arms you should move around when welding in order to control warping. Weld a little here, move to a new spot, weld a little there, and then move on again. This is the outside of the shock mount pocket. A mid-build design change was needed. I originally asked Dan to design the shock mounts for long bolts that could be accessed from the outside with a conventional box-end wrench. It turned out that the long bolts were going to bind inside their sleeves because there's no way to eliminate the warping and pulling that happens when welds cool. You can control warping and you can minimize warping, but you can't eliminate it.
    Custom Trailing Arms Welding Trailing Arms
    We've skipped way, way ahead here. Suffice it to say that when welding trailing arms you s
  • Custom Trailing Arms New Side Plates
    New side plates had to be designed and cut to accommodate the shock mount change. The old one is on top, and the new on the bottom.
    Custom Trailing Arms New Side Plates
    New side plates had to be designed and cut to accommodate the shock mount change. The old
  • Custom Trailing Arms Shorter Bolts
    The new design involved much shorter bolts. Machined weld washers were welded onto the bolt holes to reinforce them.
    Custom Trailing Arms Shorter Bolts
    The new design involved much shorter bolts. Machined weld washers were welded onto the bol
  • Custom Trailing Arms Tubes Welded
    Tubes were then welded on over the weld washers. Socket wrenches will now be needed for the shock bolts, but at least the bolts won't bind inside the trailing arms.
    Custom Trailing Arms Tubes Welded
    Tubes were then welded on over the weld washers. Socket wrenches will now be needed for th
  • Custom Trailing Arms New Side Plates Welded
    The new side plates were welded on after the shock mount tubes were in place.
  • Custom Trailing Arms Tubes Shaved Down
    Here, the new side plates are tacked on, but final welding isn't finished. The tubes were shaved down after the welding was complete. It's important to note that the shock bolts are below the centerline between the front and rear trailing arm mounting points. Below-centerline mounting minimizes the arms' twisting back and forth during compression travel. Too much twist can damage both the shocks and the trailing arms.
    Custom Trailing Arms Tubes Shaved Down
    Here, the new side plates are tacked on, but final welding isn't finished. The tubes were
By Kevin Blumer
Enjoyed this Post? Subscribe to our RSS Feed, or use your favorite social media to recommend us to friends and colleagues!

*Please enter your username

*Please enter your password

*Please enter your comments
Comments:
Not Registered?Signup Here
(1024 character limit)
Off-Road