This workshop service repair manual covers International Harvester (IH) 1566, 1568, and 1586 tractors, primarily produced in the late 1970s and early 1980s. These powerful diesel tractors were known for their robust construction and versatility in demanding agricultural applications. They feature advanced systems for their time, including diesel fuel injection, turbocharged engines, and sophisticated transmissions with Torque Amplifier functionality, designed to provide exceptional performance and operator efficiency. The engineering quality and reliability of these IH tractors made them a staple in heavy-duty farming operations, and this manual is designed to support their continued serviceability. This comprehensive manual provides detailed information for owners, mechanics, and technicians to maintain and repair the IH 1566, 1568, and 1586 tractor models. It covers all major systems, including the engine, cooling system, diesel fuel system, clutch, transmission, torque amplifier, hydraulic system, power steering, brakes, and electrical system. The manual includes preventative maintenance schedules, step-by-step repair instructions, detailed troubleshooting guides, and rebuild procedures, all supported by clear, illustrated diagrams and part number breakdowns. Its purpose is to ensure the longevity and optimal performance of these tractors through accurate and accessible technical guidance.