The Allis-Chalmers D-21 Series II, 210, and 220 tractors represent a significant part of the brand's history in the agricultural machinery sector, primarily produced during the 1960s. These tractors were designed to compete in the higher horsepower row-crop market, offering robust performance and durability that Allis-Chalmers was known for. With an estimated 70-85 PTO horsepower, they were engineered for demanding farm work, featuring diesel engines and manual synchromesh transmissions with multi-speed gearboxes. These models were well-regarded for their innovative designs and reliability, making them a strong contender against other major manufacturers of the era. This comprehensive Workshop Service Manual (WSM) provides in-depth technical information for the Allis-Chalmers D-21, D-21 Series II, 210, and 220 tractor models. It covers all essential systems, including the engine, fuel, cooling, lubrication, electrical, transmission, drivetrain, rear and front axles, steering, hydraulics, brakes, and power take-off (PTO). The manual includes detailed procedures for routine maintenance, major repairs, component rebuilds, and troubleshooting, along with essential wiring diagrams and technical specifications. Its purpose is to equip owners, mechanics, and enthusiasts with the knowledge necessary to maintain, diagnose, and repair these tractors effectively, ensuring their continued operation and longevity.