SOCIETY OFAUTOMOTIVE ENGINEERS, INC. 400Commonwealth Drive, Warrendale, Pa.15096 Development of Type C-3Torque Fluid for Heavy-Duty Power Shift Transmissions C.R.Potter and R.H.Schaefer Detroit Diesel Allison Division ofGeneral Motors Corporation Earthmoving Industry Conference Central Illinois Section Peoria, Illinois April 18-20, 1977770513 Downloaded from SAE International by University of Edinburgh, Thursday, August 09, 2018770513 Development of Type C-3Torque Fluid for Heavy-Duty Power Shift Transmissions C.R.Potter and R.H.Schaefer Detroit Diesel Allison Division ofGeneral Motors Corporation HEAVY DUTY off-highway automatic orpower shift transmissions place rigorous demands ona transmission fluid (See Figure 1).Thetorque con verter and hydraulic retarder generate heat; this requires afluid with ahigh degree ofoxidation stability andviscosity control. These qualities are necessary because sludge, varnish andchanges in thefluid viscosity canseriously impair performance ofeither manual orautomatic hydraulic controls. Bearings, gears andhydraulic pumps require good anti-wear properties andviscosity control inorder toprovide long life.Various compounds used inthe seals forpistons, shafts, andstatic applications re quire afluid which minimizes thedegree ofswell andhardening sothat theseals remain pliable for the life ofthe transmission. Because the friction surfaces ofclutches getvery hot, good control of fluid oxidation andfriction stability isrequired in order tomaintain consistent and reliable shifts. Anti-foam properties areanother very importantfluid requirement since there areseveral areas within atransmission where serious intermixing of airandfluid could occur andresult inspewing oil from the transmission breather. The hydraulic ABSTRACT The Type C-3transmission fluid specification hasbeen completed which defines tighter require ments forfluids used inheavy-duty off-highway automatic orpower shift transmissions. A laboratory testprogram wasconducted todevelop andprove-out theuprated requirements. The C-3 specification now provides forcontrol ofthefluid's effect onclutch friction retention anddurability. A redefined oxidation stability testhasbeen includedwhich calls fortheuseoftesthardware that ismore readily available. Seal-swell requirements wereex panded toinclude thelatest materials used in transmission seals. The cooperative efforts ofthe petroleum and additive industries, along with Detroit Diesel Allison, arenow providing anim proved fluid foruseinthelatest off-highway heavy duty transmissions. Copyright ©Society ofAutomotive Engineers, Inc.1977 Allrights reserved. Downloaded from SAE International by University of Edinburgh, Thursday, August 09, 20182 retarder andgears aretypical ofthese areas. Final ly,since thistype oftransmission isdrained ofoil before shipment andmay beinstorage under high humidity conditions, itisimportant that thefluid possess anti-rust properties sothattheferrous parts areprotected. Inlate 1976, theType C-3fluid specification was published which defines animproved oiltobeused with heavy-duty off-highway automatic orpower shift transmissions. This paper describes thesteps leading from inception oftheoriginal Type C specification tothe release oftheType C-3 specification. This paper alsocovers several ofthe more distinctive requirements ofthenewType C-3 specification. TYPE CFLUID EVOLUTION Themid-1940s marked theintroduction ofheavy duty power shift transmissions totheearthmoving and construction industries. These transmissions were initially lubricated with engine oil.But, the need forimproved transmission fluids became ap parent asearly field experience revealed serious fluid-related problems. The most serious ofthese wastheformation ofsludge andvarnish which in terfered with proper transmission function. After several years ofdevelopment testing and close work with the additive manufacturers and General Motors Research, theType Cspecification forheavy-duty off-highway transmission fluid