This is a step by step guide to installing avis adjusters. I modeled the beam in Autodesk Inventor so it isn't exact. It is accually a narrowed beam so note the differences. The bump stops are missing and the sway bar and spindles are removed already. Feel free to add suggestions to it.
Your beam (bus thru 79, standard beetle, ghia and thing) is set up with two torsion tubes. The trailing arms on each end are held on by a set screw that is tightened into a dimple drilled in the torsion leaves. It then has a jam nut to hold it in place.
To remove the trailing arm you must use a 19mm or 3/4 wrench to loosen the jam nut and then using an 8mm allen wrench remove the set screw.
The trailing arm will then slide out of the tube. The upper arm may be harder to get out due to the pressure against the bump stops (not modeled)
Note the set screw dimple in the leaves. It is only on the front side for the trailing arms and in the rear for the center retainer (shown later)
I usually leave one trailing arm on so that I can pull the leaves out with it. Here you can see the basic anatomy of the beam with the center retainer and the bearings.
Next I remove the center retainer set screw. It also has a jam nut.
I then use the trailing arm to pull the leaves out of the beam.
Here is a close-up of the center retainer.
Repeat the step for the lower tube.
Take the adjuster large half and here is where it get more tricky. To use this on a bus beam you will need to work it to fit the 2.5 dia tube. Two ways of doing it are to grind the top and bottom inside edges so that the adjuster will lay flatter to the tube. Another way is to heat the adjuster and flatten it a little in a vise. If you are building a drop beam for a bus you line the bottom of the slot up with the original center hole and scribe or trace the slot onto the beam. If you are building a beetle beam the original hole should line up with the top of the slot. I also scribe the outside of the adjuster as a reference later.
Repeat for the bottom tube.
Using a grinder with a cut off wheel, cut the area for the slot out of the beam but don't go outside of the outer mark for the adjuster.
Next there are several options to loosening the center retainer. It is held in place by 3 dimples. You can either drill them out which is difficult on the lower tube due to the steer pivot bracket or you can use a pipe to hammer the retainer back a forth til it moves freely. (Jeff's idea)
Once it is loose put the large half of the adjuster back in position, lay the small half on top of that and put the new larger screw in to the retainer and hold it down in position using the jam nut. With it in the correct position weld only the large half down good.
Once it is welded back the set screw out enough to reinstall the torsion leaves and center the dimple. Then tighten down the set screw. The reason you leave the set screw in partially is to keep the now loose center retainer from sliding inside the beam as you install the leaves.
Reinstall the training arms and set screw and torque then to the spec and install the jam nuts.
Wala!! You have a adjustable beam.