The Nuffield Universal Three and Universal Four series tractors, produced primarily from the late 1950s through the 1960s, represent a significant chapter in agricultural mechanization. These robust machines, powered by BMC diesel engines such as the 3.4T and 4.0T variants, were engineered for reliability and utility. Featuring a constant mesh gearbox, hydraulic lift systems, and designed for high low-end torque, they were well-suited for demanding agricultural tasks. Variants like the 3DL, 4DM, 4T, 3DT, and 4DM showcase the model's adaptability, making these tractors enduring examples of British engineering. This comprehensive service and repair manual provides in-depth technical guidance for all Nuffield Universal Three and Universal Four models, including petrol and diesel variants. It covers essential maintenance procedures, detailed troubleshooting steps, and complete disassembly and reassembly instructions for all major systems, including the engine, transmission, brakes, electrical system, hydraulics, and chassis. With detailed wiring diagrams and specific fluid specifications, this manual is an indispensable resource for owners, mechanics, and technicians aiming to maintain, repair, and preserve the operational integrity of these classic tractors.