The Hitachi ZX40U-3 and ZX50U-3 compact excavators, part of the U-3 Series, are engineered for demanding work environments. These machines feature robust diesel engines, with the ZX40U-3 powered by an Isuzu 4JG1 producing 32.1 kW (43.1 hp) and the ZX50U-3 by an Isuzu 4JG1-T producing 38.4 kW (51.5 hp), both with a 3.0 L displacement. Their hydrostatic transmissions offer variable speed control for precise operation, and their compact dimensions, including widths over tracks of 1950 mm and 1960 mm respectively, allow for maneuverability on job sites. The ZX40U-3 has an operating weight of 4075 kg, while the ZX50U-3 weighs 4790 kg, making them suitable for a range of construction and excavation tasks. This Workshop Service Repair Manual in English provides comprehensive guidance for the Hitachi ZX40U-3 and ZX50U-3 excavators. It covers essential maintenance procedures, including fluid capacities and service intervals for engine oil and hydraulic filters, along with detailed technical specifications for engine, transmission, and dimensions. The manual also includes information on troubleshooting and repair, equipping owners, mechanics, and technicians with the knowledge to maintain optimal performance and longevity of these diesel-powered machines.