I mounted the rear sway bar in a previous post and the next step was to attach it to the bellcranks. The adjustable sway bar blade accepts a 3/8” rod end. However, the other side of rear sway bar link is attached to the same 1/2” bolt that affixes the shock absorber to the bellcrank. While it would be easy to fabricate a link with a 3/8” rod end on one side and a 1/2” rod end on the other side, that would be overkill. 1/8” might not seem like a big difference, but a 1/2” rod end dwarfs a 3/8” one.
1/2” rod end (left) and 3/8” rod end (right)
It also requires a larger tube-end weld nut, jam nut and tube which adds weight and bulk making it more difficult to clear the shock absorber spring. I spent a couple of nights scouring the Internet for a unicorn — a rod end with a 1/2” bore and a 3/8” male thread. If it exists, I couldn’t find it.
I considered machining a 3/8” shoulder and a 3/8” thread on the tip of a 1/2” Grade 8 screw, but I’m not comfortable machining threads yet. I then realized that a shoulder screw would be a better starting point. They are comparable in strength to a Grade 8 screw and McMaster offers 1/2” shoulder screws with a 3/8”-16 thread with grip lengths in 1/4” increments. I purchased two with a 4” grip which was long enough to allow the link to clear the shock absorber. All I needed to do was turn 1/8” off of the last 1” of the grip in the lathe.
That should be easy, right? Nope! No matter what I tried I couldn’t get a good finish. I had purchased an indexable carbide tool set because I didn’t want to learn how to grind High-Speed Steel (HSS) tools. Apparently, carbide likes much higher speed and feed rates than my lathe can do (think CNC). It worked fine on aluminum, but it wasn’t working on this grade of steel. After doing a little research, I discovered Arthur R. Warner Co. who offers indexable HSS inserts. I purchased one of their tool sets and they provided an excellent finish.
Shoulder screws are more difficult than normal screws to install through suspension parts because the shoulder has a 90-degree edge that gets hung up on anything that isn’t perfectly aligned (e.g., safety washers, rod end’s mono ball, etc.). To mitigate this issue I chamfered the 90-degree edge.
Stock shoulder screw (top) and modified shoulder screw (bottom)
The next step was to design and fabricate a bracket to position the link 1.3”from the bellcrank and to put the shoulder screw in double shear.
I laser cut a plate from 1/8” 4130 that attaches to the underside of the bellcrank via the existing 1/2” bolt holes. Using the lathe, I machined a spacer to fit between the bellcrank and the misalignment washer. It’s critical that the misalignment washer binds on the bellcrank (via the spacer) and not the face of the shoulder screw. I used 1”4130 rod to match the OD of the misalignment washer and drilled a 1/2” through hole. To reduce the weight of the piece I machined the all but the last 0.4” of the ID to 3/4”. The lathe would have been ideal for this, but my Jacob’s chuck maxes out at 1/2”.
Instead, I mounted a three-jaw chuck to the mill and used a 3/4” 4-flute end mill. Given the hard alloy steel and cheap end mill I was worried about chatter, but using the online speed/feed calculator (460 RPM) and the quill (as opposed to the z-axis handle) allowed me to cut it like butter. I assume that this was due to the 1/2” hole already being drilled. I had to stop the mill several times to remove the swarf which is as sharp as shit… yeah, I managed to cut my finger which wasn’t a big deal because the mill was off. I had become comfortable dealing with aluminum and this was one of those important lessons which could have been much worst. After employing a Band-Aide, I used a 3/4” countersink to chamfer the spacer’s internal face to make it easier to feed the shoulder screw through it.
1” 4130 rod, 3/4” 4-flute end mill and sharp-as-shit swarf
4 laser cut parts; base plates and double-shear plates. 4 machined parts; from left to right, spacer (top view), spacer (bottom view), post (top view), and post (bottom view)
I machined a post to support the double shear plate from 3/4” 4130 rod. One end was drilled and tapped for 3/8”-16 and, similar to the spacer, the other end was machined with a 1/2” end mill to reduce weight.
Because all of the welding was going to be done at one end, I fabricated a simple welding jig from consisting of a plate and two spacers. I used aluminum because it’s an excellent heat sink. ER70S rod to add some large tacks that were structurally strong enough, but minimized the chances of warping. I wanted the full circumference welded so he used silicon bronze rod because we didn’t need the strength and it requires half as much current which equates to a lot less heat.
Abe welding on the jig
The custom parts; bellcrank bracket, double shear plate and modified shoulder screw
Exploded parts view
The links were fabricated from 4130 tube, 4130 tube-end weld nuts and stainless steel hex nuts. The aluminum tubes located between the sway bar link and chassis are for the front and right-rear air jacks.
The adjustable blade extends down from the top left corner
The next step is to run the control cable.