Automatic Transmission Fluid—a Dynamic Material Keeping Pace with Ever-Changing Requirements

Abstract

With Oldsmobile's introduction of the semi-automatic transmission in 1937 came the need for a transmission fluid with greater resistance to sludge and varnish formation than had been hitherto available. In 1940, when Oldsmobile introduced it, the Hydra-Matic transmission demonstrated a need for other fluid characteristics, namely: (1) prevention of excessive foaming which results in heat build-up, volume expansion, and loss of the fluid from the transmission; (2) fluidity at temperatures down to −40 F to prevent clutch plate failures due to burned facings; and (3) controlled lubricity, to assure smooth clutch engagement and to discourage stickslip, which results in clutch engagement squawk. Other important transmission fluid characteristics are corrosion protection, lack of an objectionable odor, and nontoxicity. It must be compatible with synthetic rubber seals, with previous as well as current production transmissions, and other previously qualified transmission fluids. Although reference will be made to the type A fluid qualification program and to some of its test procedures and history, the purpose of this paper is to relate briefly the previously untold experiences encountered during the 25-yr development of automatic transmission fluid.