Issue link: http://read.dmtmag.com/i/859318
Transmission Fluids Background & Properties castrol.com/GPS 800 255 4417 May 2025 GPS Types of Transmissions & Diagnosing Problems A premium TO-4 powershi transmission fluid should: • Provide control over the 7 different frictional elements, both metallic and non-metallic, commonly found in a powershi transmission; • Eliminate brake noise; • Reduce wear of elastomeric material; • Prevent slippage; • Encourage stable performance over the life of the fluid; • Inhibit metal-to-metal contact while protecting vane pumps, planetary gear sets, final drive gears and bearings from premature wear; • Offer foam protection to guard against fluid loss; • Promote low temperature performance to reduce start-up wear; • Control oxidation to prevent deposit formation that can restrict lubrication; and • Maintain excellent shear stability to ensure consistant protection from wear. Diagnosing TO-4 Type Powershi Transmission Problems Improper use of an ATF or tractor fluid in most powershi transmissions will produce burnt and/or slipping clutches, inadequate holding capacity for both brakes and clutches and insufficient wear protection for gears. Caterpillar pioneered the TO-4 specification for its off-highway powershi transmissions. Fluids meeting this specification have been factory fill on all CAT powershi transmissions since 1991, and there is little comparison between the TO-2 and TO-4 specifications. e TO-4 specification defines frictional capabilities in-depth and combined with the anti-wear properties and added gear protection, a premium TO-4 fluid maximizes powershi transmission life and operating efficiency. Some agricultural equipment such as medium and large size tractors also employ powershi transmissions. e friction material of the shiing clutches in this application are selected to function properly with tractor hydraulic fluids, which have a low static coefficient of friction to prevent chatter or squawk in the wet brakes used in these machines. Hydrostatic Transmissions A hydrostatic transmission uses fluid to transfer power from the engine to the drivetrain through a hydraulic pump and motor. A transmission of this type consists of a pump connected to the engine generating fluid power to drive a hydraulic motor, which is connected to the axle and/or driving wheels. If the displacement of the pump and motor were fixed, the transmission would merely act as a gearbox to transmit power. Most hydrostatic transmissions use a variable displacement pump or motor in order to vary speed, torque or power and provide transmission function. erefore, the fluid used in a hydrostatic transmission only needs to function as a hydraulic fluid, as there are no clutches or gears to lubricate. Fluids commonly used in hydrostatic transmissions include hydraulic fluids, D7 ecastrof