This service repair manual covers the Case D Series wheel loaders, including models 21D, 121D, 221D, and 321D. These machines are engineered for robust performance and reliability in various operational environments. The D Series represents a commitment to durable construction and efficient functionality, making them a dependable choice for demanding tasks. This comprehensive English-language manual provides essential information for maintaining and repairing your Case D Series wheel loader. It details general information, service data, engine and transmission specifics, axles, steering, brakes, hydraulic systems, electrical systems, frame components, and fittings. The manual includes diagnostic procedures, troubleshooting guides, and servicing instructions, supplemented by real photo illustrations, diagrams, and schemes to ensure clarity and accuracy for owners and technicians alike.