A site dedicated to the Ford N Series Tractor. The Sherman brothers soon built the Sherman auxiliary transmission. The unit was a runaway success, and more than 100,000 units were sold by the late 1940s. Overdrive or Underdrive. The transmission is designed to fit into the housing between the engine and the factory transmission.
Installation is simple, and the only exterior evidence is a shift lever.
There were a limited number of transmissions that were designed to use a cable to shift. These models were not popular because the cable would rust and seize. The tractor is split between the engine and the transmission, the input shaft is removed, and the Sherman is installed in it's place. The Sherman makes the standard Ford transmission a multi-range unit. The step-down model gave the operator the choice of using the standard gear, or flipping the lever of the Sherman to activate a low range useful for heavy pulling or fieldwork.