TEST METHODS FOR DETERMINING ANTI-SHUDDER DURABILITY OF AUTOMATIC TRANSMISSION FLUIDS

Anti-shudder characteristics are an important part of automatic transmission fluid (ATF) performance. Anti-shudder performance has two aspects, initial friction aimed at the prevention of “green shudder” and anti-shudder durability which is the prevention of shudder at high vehicle mileage. Different methods of measuring anti-shudder durability give different results. We have found that some fluids give very acceptable performance when measured in a Low Velocity Friction Apparatus (LVFA) test, such as a JASO M349-2001 [1] , do not give good results when measured in a method that includes high energy engagements and oxidation. This apparent anomaly in test results is due to unexpected behavior of certain fluids after oxidation. The observation is a cause for concern relative to the widely accepted JASO method.