This manual covers the Hitachi ZX40U-3 and ZX50U-3 compact excavators, part of the U-3 Series. These machines are engineered for reliable performance in various construction and landscaping applications, featuring robust diesel engines and pilot-operated hydraulic controls for precise operation. Their compact size and versatile capabilities, including significant digging depth and reach, make them efficient tools for demanding job sites. The ZX40U-3 and ZX50U-3 are designed to deliver consistent power and durability, reflecting Hitachi's commitment to quality and operator productivity. The purpose of this Workshop Service Manual (WSM) and Repair Manual is to provide comprehensive guidance for the maintenance, repair, and servicing of your Hitachi ZX40U-3 or ZX50U-3 excavator. It details essential procedures, technical specifications, and troubleshooting information necessary for optimal performance and longevity. This manual is an indispensable resource for owners, technicians, and mechanics, ensuring that all maintenance and repair tasks are performed correctly and safely, thereby maximizing the operational life and efficiency of the equipment.