This paper presents results of an SAE #2 Machine study of several factors influencing wet friction material operation. By adjusting test condition, it is shown how plate deflection, spacer roughness, power loading, energy loading, etc. can produce mechanical and/or thermal distress of the friction material. In comparative testing, it is also shown how these problems can be reduced or eliminated by proper selection of friction material, groove, assembly and spacer plate geometries, oil type and flow, etc. The purpose of this work is to contribute to understanding of wet friction couples to permit identification of the mode of failure (1) to provide corrective action in present designs and (2) to optimize future design.