This workshop service and repair manual covers the robust Allis-Chalmers D21, D21 Series II, Two Ten (210), and Two Twenty (220) tractors. Manufactured by Allis-Chalmers, a company renowned for its durable agricultural and construction equipment, these tractor models represent a significant part of the brand's later offerings, produced primarily in the late 1960s and 1970s. Known for their power and utility, these machines were built to perform demanding tasks. This manual provides comprehensive resources designed to help maintain their operational efficiency and longevity, positioning it as an indispensable tool for owners and technicians. This manual offers in-depth and highly detailed information essential for the servicing and repair of key tractor systems. It covers a wide range of topics from routine maintenance procedures and adjustments to complete overhaul and rebuild instructions for major components such as the engine, transmission, and hydraulic systems. Specific areas include detailed guidance on brakes, clutch, cooling system, diesel fuel system, differential, electrical system, final drive, front system, power lift, power steering, power take-off, and steering system. Furthermore, it provides crucial technical specifications, torque values, fluid capacities, and troubleshooting guides, all presented with clear instructions and detailed visual aids to facilitate accurate and efficient repairs.