AUTOMATIC TRANSMISSION – ZF HP 44-2-14 DESCRIPTION AND OPERATION The converter housing cover has four threaded bosses which provide for attachment of the engine drive plate which is connected to the engine crankshaft. The threaded bosses also provide for location of special tools which are required to removed the torque converter from the bell housing. With the impeller welded to the converter housing cover, the impeller is therefore driven at engine crankshaft speed. Impeller The impeller outer body has a boss with two machined slots. The boss locates over the transmission input shaft and the slots engage with two tangs on the fluid pump. This arrangement allows the fluid pump to be driven at engine speed. The impeller comprises a row of blades attached to the outer body. The root of the blades collect fluid which flows by centrifugal force around the curved outer surface of the impeller to the tip of the blades.