Abstract Improving vehicle fuel efficiency is a key market driver in the automotive industry. Typically lubricant chemists focus on reducing viscosity and friction to reduce parasitic energy losses in order to improve automotive fuel efficiency. However, in a transmission other factors may be more important. If an engine can operate at high torque levels the conversion of chemical energy in the fuel to mechanical energy is dramatically increased. However high torque levels in transmissions may cause NVH to occur. The proper combination of friction material and fluid can be used to address this issue. Friction in clutches is controlled by asperity friction and hydrodynamic friction. Asperity friction can be controlled with friction modifiers in the ATF. Hydrodynamic friction control is more complex because it involves the flow characteristics of friction materials and complex viscosity properties of the fluid. This paper shows how NVH and torque capacity can be controlled by optimizing the flow characteristics of friction materials and the complex viscosity of fluids. Introduction There is a continuing need to improve vehicle fuel efficiency and reduce vehicle emissions. There are many new hardware technologies being considered to meet these needs including improvements to engine technology and changes to the structure and operation of transmissions. Changes to engine technology to improve efficiency and emissions can result in an increase in torque input into the transmission. In the transmission, aggressive shift logic and an increase in gear settings are also being implemented and these af fect torque control through the transmission [ 1, 2, 3]. 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 can lead to NVH (noise, vibration and harshness). Considerable research has been performed to understand torque fluctuation or NVH control in clutches [ 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42]. 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 torque fluctuations is quite complicated [ 4, 5, 6, 7]. Equation 21 of reference 4 describes the torque conditions required to reduce fluctuations: the gradient of torque with respect to slip speed, dT f/dωslip, must be positive to eliminate torque instabilities. The first term in Equation 21 is always positive. The last two terms relate to changes in film thickness in the clutch with changes in slip speed. These last two terms can be positive or negative depending upon whether a clutch is being engaged or disengaged, therefore these terms will fluctuate between having a positive or negative sign during normal operation of a transmission. This leaves the second two terms in Equation 21 as a means to control torque fluctuations and NVH. The second term describes torque controlled by flow of fluid in the clutch (hydrodynamic torque/friction) [ 8, 9, 10, 11 , 12, 13, 14, 15, 19 , 21, 26, 28, 29, 33]. The third term describes torque controlled by interacting surfaces (asperity torque/friction) [ 8, 9, 10, 11 , 12, 13, 14, 15, 19, 21, 26, 29, 33, 35]. Equation 21 [4] The material, operational and fluid properties that affect hydrodynamic and asperity torque are more explicitly described in Equations 23 and 24 of reference 4. The values inside the parentheses in these equations are always positive. This leaves the familiar friction versus speed terms (dλ/dv and dμ/dv) as the Effect of Fluid Flow through Cl