Nylon is used as a material in the design of various components of automatic transmissions, namely pump rotor guides and thrust washers. These nylon components must be compatible with automatic transmission fluid (ATF). Field and laboratory cycling testing of experimental ATFs showed that nylon components in contact with ATF underwent color changes and exhibited loss of tensile strength. A laboratory bench test was developed to simulate these occurrences. The end-of-test nylon 6 and nylon 6/6 test pieces, the cycling test pieces, and the field parts were analyzed. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) data show that the crystallinity of the nylon materials increased, probably from decomposition of plasticizer, and the increasing crystallinity is responsible for the loss of tensile strength. With the field test pieces, degradation of the actual nylon component followed the plasticizer decomposition. Nylon test pieces placed in an oven showed the same changes in color and tensile strength as the field pieces and bench test pieces. From this, it was concluded that the nylon changes were not due to chemical interactions with ATE but rather from heat. The ATI;actually reduced the thermal effects on the nylon. This paper outlines the thermal and X-ray analyses of the nylon test pieces to illustrate the interaction of nylon 6 and nylon 6/6 with automatic transmission fluids.