In the recentlly posted kingpin shimming video, the upper arm on the car that's being used for illustration is clearly too tight. In order for the front suspension to function at its best, the upper arm should pivot on its hingepin freely enough so that it will drop down just by its own weight. Possible (and typical) causes for the upper arm binding are: the hingpin itself often fits too tightly in the upper arm. Either that or else the stack of caster shims may be slightly too thick. Both are common problems on 1/12th scale cars, but thankfully both are fairly easy to address. To free up the hingpin, just run the appropriate size reamer or pin-vise drill bit thru the plastic upper arm, opening up the hingpin holes just enough to allow the hingpin itself to slide thru freely but still without any slop. To eliminate binding from the caster shims, you can rub just one of the little shims per side on an emory board or fine sandpaper to reduce it's thickness slightly. Remove only enough thickness so that the stack of caster shims can slide into place without binding the upper arm. Once the hingpin fits nice and the caster shim stack has been adjusted to yield the correct dimension, the assembled upper arm should drop nice and free, without any binding, and also without any slop or excessive play.