Abstract Good shift quality in automatic transmissions is important for fuel efficiency, driver comfort, and performance. Maintaining this performance over the life of the vehicle is also important. Typically lubricant development focuses on reducing viscosity and friction in order to reduce parasitic losses. In an automatic transmission other factors are also important for good performance, primarily due to the shifting clutches and the torque converter clutch. A high level of friction is desirable for torque capacity and a steady decrease in friction as sliding speed (rpm) decreases is necessary for both good shift feel and good friction system durability over the lifetime of the vehicle. Changes in the friction system over time that result in a lowering of the friction level, particularly at higher sliding speeds, compromise the performance of both types of clutches. In this paper , an experimental shifting clutch durability study demonstrates the impact of changes in friction materials on the mu-v curve and how small changes in a fluid can control these changes. Introduction Transmission designs are evolving to provide better efficiency through a larger number of ratios, faster shift times, and improved comfort during shifts. These new designs have put increased performance demands on shifting clutches, which in turn require advances in the materials used [ 1,2]. Among these materials are the automatic transmission fluid (ATF) and the clutch friction material. These two key elements of the transmission not only need to meet high performance requirements on their own, they also need to work well together to preserve the good performance of the transmission as a whole. For this reason we consider the friction system - the combined friction material, ATF, and testing conditions used - when evaluating performance. Changes in the interactions of these elements can be the difference between good and poor performance. Improper management of torque flow through a transmission can result in undesirable torque fluctuations often referred to as shudder or hunting. Shudder and hunting can cause noise and vibrations in a transmission and make shifts between gears harsh, so collectively these torque fluctuations are called NVH (noise, vibration and harshness). Considerable research has been performed to understand NVH control in clutches [ 3, 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25]. These studies focus on the effect of three main factors; friction material properties, operational conditions and automatic transmission fluid (ATF) properties. The interplay between material properties, operational conditions and fluid properties to control NVH is quite complicated [ 3,4]. Since an important factor in providing both high torque and good NVH characteristics is the roughness and porosity of the friction material [22], changes in these characteristics in performance testing may be correlated with changes in performance. Higher roughness and porosity inhibit the formation of a hydrodynamic film at high sliding speeds [ 8, 9, 16, 21], so that boundary friction dominates. The friction coefficient remains high at all speeds for good torque transfer. Conversely, the phenomenon commonly referred to as “glazing” suggests a loss of material porosity and smoothing of the surface. This low surface roughness results in a reflective or shiny appearance. Reduced porosity leads to lower friction levels at high sliding speeds [ 8, 22]. The durability of friction systems designed for automatic transmissions may be evaluated using a variety of industry-standard tests. There are two basic types of friction durability testing - continuous drag testing and repeated engagement cycling. In the former, a friction system is subjected to continuous sliding under pressure or continuous torque transfer in order to wear the system. In the latter, a high speed braking engagement cycle is