The reason why Sachs Ergo levers don't work with Shimano rear derailleurs has nothing to do with cog spacing. It is because the design of the Sachs New Success rear derailleur is fundamentally different than a Shimano derailleur in terms of mechanical advantage.Sachs New Success, or at least the 2 that I have, have a mechanical advantage of 1.43:1. Shimano from that era are 1.67:1.