An M.G. Locost Build

October 24, 2011

We spent almost all day Saturday filing control arm tubes to fit our new and improved UCA jig, and we got some amazingly good results, at least based on our own definition of good. And results. Unfortunately, after consulting the plans, we think we might have to make some changes. The finished upper control arms are 9-3/8” long with the rod ends screwed in just about as far as they'll go. There's only two threads showing, which means we might be able to adjust the arms as short as 9-5/16”, without jam nuts. But that’s it. And that’s a problem.

  UCA locked in the jig
click to enlarge

After checking and rechecking the plans, we're pretty confident that with the lower control arms at 12-1/2” and the upper arms at 9-3/8”, we’ll end up with zero degrees of camber, which is okay but not perfect. To adjust the camber to -1 degrees, which is preferred, we'd need to shorten the UCAs to 9-3/16”. Which is about an eighth of an inch shorter than they’ll go right now. To set the camber at a more aggressive -2 degrees, we'd need to shorten the UCA to 9". Which is impossible. So it's not looking too good right now.

You might think we could just chop half an inch off the threaded tubes to shorten the A-arms, but that won't work because the rod ends are almost bottomed out already. We think there needs to be a minimum number of rod end threads engaged in the control arm, probably at least half, or 15, which means the range of adjustment should be the remaining 15 threads. This works out to 3/4", which gives us a camber range of of about four degrees. I don’t think we'll need all of that—we plan to start at -1.5 degrees and probably won't vary from that by more than half a degree either way—but that assumes we get everything built very close to the plans, and what are the odds of that happening?

Plans for new sleeker UCA  
click to enlarge

All things considered, we think the starting length for our upper control arms should be right at 9-1/4”, with at least eight threads showing. According to our new calculations, which probably shouldn't be trusted since that's what got us into this mess in the first place, a 9-1/4"-long control arm with eight threads showing would get us to -1 degree of camber with five threads showing, and we would then have those five threads for fabrication tolerance, or even a jam nut if we got lucky, which we certainly wouldn't expect but there's always a first time.

The control arm in the jig is now 9-3/8” long with two threads showing. To get it down to a length of 9-1/4" with eight threads showing, we would need to shave everything down until we have at least ten threads showing. We should be able to do this by shaving the threaded tubes down another 1/8”, and the main tubes by about a quarter inch, and if you didn't follow all of that, don't worry, I'm not sure we did either, but rest assured we'll figure it out the same way we always do, in PowerPoint.

In better news, we were at our local hardware store the other day and found a small half-round file with a 3/4" diameter on the round side, perfect for filing those 3/4" fish-mouth ends just right. Up to now we've been sort of faking it with the other files, and we were a little concerned about it. No more. This may not seem like such a big deal to you, but it's these little things that keep us going.


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