Quick Adjust Control Arms

for Whippet and Locost

IMPORTANT NOTE: These control arms are not yet for sale. They have not been load tested, and structurally they are quite a departure from "the book" so significant testing is in order. The following article is to show you what we're working on, and to inspire our fellow Locosters.

UPDATE 10/29/06: test results are now posted, at
[Sage advice>Tests>Control Arm Tests (preliminary)]


We're working on improving our front suspension, starting with the upper control arms. We came up with this particular version partly so people won't mix up Kinetic 7s with CMC Locosts, but mostly it's to reduce the effort of suspension adjustment. On these, most adjustments can be made without removing the rod ends from the chassis pickup points. Also, we don't have to respace the rod ends when changing alignment. Here's a sample…

…and here's the CMC version of our other style, for comparison purposes.

The obvious difference is the tab welded to the front tube and the clevis threaded into the rear tube. The tab is laser cut from 1/4" mild steel plate. Another difference is, the spindle end of the front tube is one piece, rather than having a threaded slug butt welded to it.

Fabrication is a bit of a chore, but to quote Albert Einstein, "Everything must be made as simple as possible, but no simpler." To eliminate the slug, we start with a 1" OD, 1/2" ID DOM steel tube and bore all but the last 1-7/8" of it to 3/4" ID. A 3/4" insert is welded into the chassis end of the tube, which is drilled and tapped for a right thread 1/2"-20 rod end. The tab is welded to the outboard end, and then the unbored length of tube is drilled and tapped for a left thread 5/8"-18 rod end or track rod end. It probably doesn't make a difference, but if this way eliminates one more critical weld, I'm all for it.

Another complexity is, we use a lot of taps to make these control arms. On the old version, the arm had to be removed from the chassis or spindle for any adjustments (and removed from both for many adjustments), and on this version we use right and left threads (left thread inboard on the rear tube, left thread

outboard on the front tube), so the rear tube length can be adjusted by turning the tube, and the front tube length can be adjusted by turning the rear tube until it's free of its clevis and rod end (or removing the AN6 bolt holding the clevis to the tab) and turning the front tube. Each revolution of the front tube moves the rod end and ball joint together/apart by about 1/10"* which can put you within about half a degree of your target for camber, but once you break out the tire pyrometer, you'll be unbolting the front ball joint from the chassis to get exactly what you want.

Sheesh, I'm writing like it's a product already. I'm getting ahead of myself; the only problem I forsee is this part will be slightly less locost than the one piece weldment, but hey, if I could forsee all the possible problems, we wouldn't have to test at all. When it has passed its static tests, we'll be looking for a few good test drivers, and then we'll see if it's ready to add to our parts list.

or more

* 0.10555... to be exact; 0.050 for the rod end, 0.0555...for the track rod end. Since the tab has to come back to the same spot, one can only do whole turns of the forward tube. For fine adjustments, remove the bolt holding the rod end to the chassis; the rod end can then be adjusted in half turns (.025" per half turn).

For ridiculously fine adjustments, turn the inboard rod end in a turn and the outboard track rod end out a turn, which gives a net gain of 0.0055...