The operational coupling reliability level attained with the smaller couplers is determined by how accurately the couplers can be, and are centered/aligned at the moment when the couplers meet. The smaller gathering range of the smaller couplers reduces the room for error in this regard, requiring the operator choosing these couplers to pay even more attention to the biggest endemic culprit in the allowing of any given car to be off center: excessive axle/wheel-set end play. The usual excessive coupler shank length offers even more opportunity for poor centering.

Coupler droop is a big problem with any coupler using the standard "Athearn" or Kadee boxes, and IMHO is one of the biggest root problems with uncouplings/derailments, i.e. couplers pulled into distortion, allowing their draft angles to work into an over-ride; or more catastrophically, a coupler magnetic glad hand pulled down to snag the next closure rail. The droop in the proprietary #78 box is also excessive.

That except for the short shank #153 semi scale couplers, the other Kadee semi scale couplers (58, 78) are on prototypically excessively- long shanks. The weight of the heads sticking on the ends of these long lever arms do nothing but exacerbate the drooping problem. IMHO, from a prototypical point of view, seeing a coupler head sticking out like akin to a head on the end of a pole destroys any advantage that a small coupler head might otherwise provide. In this regard, if short shanks are not a choice, you are better off sticking to regular sized couplers, where the large heads pretty much hides the fact that the shank is too long, and that it is in fact sticking out of a grossly oversized coupler box.

Personally, I see no visual advantage at all to using semi scale couplers of any variety unless the shanks are short.

Denny


Denny S. Anspach MD
Sacramento