The Hitachi ZX40U-3 and ZX50U-3 compact excavators, part of the U-3 Series, are engineered for robust performance and reliability in various construction and landscaping applications. These diesel-powered machines feature a water-cooled engine and a hydrostatic transmission with variable speed ranges, offering precise control and efficiency. Their compact design, with operating weights ranging from approximately 4,000 to 5,200 kg, makes them versatile for confined job sites while maintaining significant digging and lifting capabilities. This Factory Service Repair Manual provides comprehensive guidance for maintaining and repairing the Hitachi ZX40U-3 and ZX50U-3 excavators. It covers essential information including detailed maintenance schedules, fluid capacities, and technical specifications for the engine and hydraulic systems, which utilize variable displacement piston pumps. The manual is designed to assist owners, technicians, and mechanics in ensuring the optimal performance, longevity, and safe operation of these excavators through clear procedures and diagnostic information.