/unif02aNow at RJ Lee, Pittsburgh, PA /unif02a/unif02aNow at Daimler, Auburn H ills, MIABSTRACT One of the most common failure modes for a friction interface is the accumulation of glaze on the frictionmaterial surface. Until recently, our analysis of glazechemistry has always been consistent with thedegradation of detergent, antiwear and extremepressure additives in the oil. These additivedegradation products are readily identified by thepresence of Ca, P, S and Zn in an EDS analysis. Inthese cases the loss of friction performance,characterized by a gradual fade in friction coefficientand the concomitant development of a negative friction-speed gradient, is directly related to the loss of surfaceporosity due to the accumulation of glaze on the frictionmaterial surface. Over the past few years, the drive for better fuel economy in passenger cars has led to the introduction oflower viscosity oils possessing high viscosity index andshear stability. We have observed that these fluids alsocan lead to glaze accumulation on the friction surface.However, for these new oils, under certain conditions,the glaze is a consequence of the viscosity modifieradditives. The association of the glaze to this additivetype is more difficult to establish due to the absence ofunambiguous indicator elements. To correctly identifythe additive chemistry responsible for this glaze wehave used Evolved Gas Analysis; a technique involvingthe volatilization of the glaze and subs equent identification using a coupled Gas Chromatograph –Mass Spectroscopy technique. In this paper we contrast the glaze chemistry arising from conventional fluids (traditional ATF viscosity) withthat of the newer, lower viscosity fluids. We providedata suggesting that the failure mode is not only relatedto the accumulated loss of surface porosity but also thedeactivation of the friction surface (loss of surfaceactive sites). We then discuss how this new fluidchemistry influences the formulation of new frictionmaterials.INTRODUCTION It is our experience that the most common failure modefor friction plates is the formation of glaze on the frictionmaterial surface. As the glaze accumulates, it reducesthe surface porosity which can then result in thedevelopment of a negative friction-speed gradient(rooster tail) [1]. It is known that glaze originates fromthe fluid [2, 3, 4]. Previously we have specificallydefined glaze as the deposition of fluid degradationproducts on the friction material surface and described aset of analytical protocols to detect and quantify theglaze [3]. Among the methods employed to detect and quantify glaze, EDS (Energy Dispersive X-ray Spectroscopy) isused to identify the presence of elements associatedwith the lubricant additive package. These elements,Ca, P, S and Zn, are readily detected with EDS andindicate the presence of detergent, antiwear andextreme pressure additive degradation products on thefriction surface. Antiwear and Extreme Pressure additives are designed to react with metal surfaces at elevated temperatures.Dithiophosphate antiwear additives thermally decompose at temperatures below 200 /unif0b0C while disulfide and polysulfide extreme pressure additives thermallydecompose above 200/unif0b0 C [5]. During engagements and continuous slip conditions, clutch interfaces can reachinstantaneous temperatures in excess of 300/unif0b0 C. This is well above the stability of lubricant com ponents and specifically is above the decomposition temperatures of the antiwear and extreme pressure additives. Glazeformation therefore is generally associated with thermalevents. Prolonged exposure to elevated interfacetemperatures leads to thermal degradation of additivesand their subsequent deposition onto the frictionmaterial surface. It is not surprising then, that the fluid’spropensity to glaze is related to the thermal stab ility of the antiwear and extreme pressure additives.2008-01-2395 The Effect of Lower Viscosity Automatic Transmission Fluid on