Of the many automatic transmission components which are sensitive to the effects of the transmission fluid, the ones which possibly have the most complex interrelationship with the fluid are the clutches. Oil properties affect clutch performance, and clutch plate characteristics affect oil function.Several experiments designed to study fluid flow through a rotating clutch were conducted by the author. Fluid flow between a rotating grooved plate and a glass reaction plate was photographed. Viscous drag as a function of groove pattern was developed. And interface temperature as a function of flow was determined at various energy levels.From this information a general discussion is presented which shows that the static and dynamic coefficients of clutch friction can be altered by changing the fluid composition. From this, in turn, the main point is made-that is, as fluid properties must be considered in the design of automatic transmissions and their components, the transmission user must follow the manufacturer's fluid recommendation if optimum transmission performance is to be achieved.