[Ron Sutton]

Originally Posted by preston

Ron if you have time could you indulge one question from me -

Maybe its just a feature of the TA2 design, but it seems the arm design on this clip went out of the way to put the lower rod ends in a single axis. To me this is normally done on OEM style arms so that they can use bushings. With rod ends, it seems like it doesn't matter that much how you align the pivots (for example in your GT clip) since they will articulate. I'm also wondering if that's why the front pivot is skewed as it looks like there would be still be clearance if it came in straight from the ball joint along the FACL, or at least very close. Even though that arm is plenty stout, the amateur engineer in me just see's a big bend right in the load path.

Is there anything you're willing to share on why or why not one would want to keep rod end pivots on axis vs just putting them in the correct 3d space ? And was this skewing of the FLCA pivot mostly done for clearance ?

Hi Preston,

This might be one of the more technical questions I've received. You're correct about part of it & incorrect about parts of it.

Let's get the incorrect items (which I have bolded in your text above) out of the way ...
a. The front LCA mount & rod end is in the optimum location & is in line with the load forces better than if we had run the rod end straight out to the LBJ, like we do with my GT front end. On the GT front end, which uses 2-piece LCAs, I had to really be cognizant of the forces pulling on the rod end at an angle not true with the rod end design. I handled this with both design & material solutions. With the TA LCA here, the forces pulling on the front LCA rod end are closest to being in line with the front LCA rod end.

So you may have a skewed view of which direction the forces are actually pushing & pulling. The forces are not pulling straight out from the rod end to the LBJ. The forces are pulling out & forward on the front rod end, in an arc, based on the rear LCA rod end acting as a pivot location for the LCA ... like a sideways rocker arm. See the photos below.

b. I am not clear on what you mean by the "big bend right in the load path" ... as the front rod end & LCA receptacle for the rod end are very close to the load direction. *You can't be perfect with a non-articulating part (top view), as the load pulling on the front rod end is in an arc, not straight. The rod end in this LCA is at the optimum angle & the LCA design itself is triangulated & braced internally to handle the circular loading that occurs.

c. If by skewing, you mean why are the LCA pivots on the same plane as each other to form a true pivot axis? ... the answer is no, this wasn't done for clearance. It actually hurt clearance a bit & forced the rack forward a bit more then the GT. Is was done so the special adjusters & rod ends on the LCA would function properly over a wide range without binding.

Any time you have a 1-piece LCA, if you don't put the rod ends on the same pivot axis, you have a very small window or sweet spot the rod ends have to be to bolt up to the frame. There is less than a turn or two ... to adjust the rod ends without binding in a 1-piece L:CA if the rod ends aren't parallel. If the rod ends run at opposing angles on a 1-piece LCA ... if you adjust the rod ends to adjust camber, caster and/or track width ... we'd bind up the rod ends in the LCA frame buckets with very little adjustment. So I don't design 1-piece LCAs with the rod ends at opposing angles, only parallel.

The trick adjusters on this 1-piece LCA for my TA & TA2 front suspensions (you can see them as a Gold Hex on the frame side of the LCAs) have the rod ends screw into them, with a jam nut on the other side. The cool part about these is you can adjust track width, camber or caster, at the LCA quickly & easily. They have a wide range of adjustment because the rod ends are parallel. We couldn't achieve that if they were at opposing angles in a 1-piece LCA.

With most LCAs using rod ends, you have to unbolt the rod end from the frame bracket ... loosen the jam nut ... make an SWAG length adjustment by threading the rod end in or out either in half or full turns ... then bolt it back up & see if we hit the target on the camber, caster or track width changes we're looking for. With these special adjusters on the TA & TA2 LCAs, we can loosen the jam nut(s) and turn the gold hex adjuster ... to adjust camber, caster and/or track width .... without unbolting the LCA rod ends from the frame. Quick, easy & more precise.

To clarify, we can run the rod ends at opposing angles in a LCA. If it is a 1-piece LCA, you just don't have much rod end adjustment without binding. So on my GT cars where I do run the rod ends at opposing angles, the LCAs are 2-piece. There is a main LCA that comes straight out from the frame to the LBJ ... and a strut rod that comes from the chassis to the LCA mounting point. That mounting point is what allows us to adjust the rod ends without creating bind like a welded 1-piece control would. The bolt together design simply allows us to adjust the LCA rod end at the frame mount ... and/or the strut rod rod end at the frame ... a pretty good amount, without binding the rod ends.

As you can see from the photos, the load arc is more in line with the rod ends being parallel, and not when the rod ends are at opposing angles. So when we build 2-piece LCAs, we need to insure the design & materials are super strong, and the rod end is a wide body chromoly rod end, not the standard mild steel or even narrow body chromoly. The wide body provides more contact area & control of the monoball in the rod end body, which is critical, because this rod ends sees more side loading.

Make sense?

.