This comprehensive workshop manual covers the 4L60, 4L60-E, and 4L30-E automatic transmissions, widely utilized across numerous vehicle makes including Buick, Cadillac, Chevrolet, GMC, Holden, Hummer, Pontiac, Saab, Acura, BMW, Honda, Isuzu, and Opel. These robust transmissions, an evolution of the successful THM700R4, are known for their versatility and ability to handle significant torque, making them a cornerstone in a vast array of vehicles from the early 1990s through the late 2000s and beyond. They are commonly paired with V6 and V8 engines, offering a 4-speed longitudinal automatic configuration with electronic control for enhanced shift quality and efficiency, featuring a lock-up torque converter for improved fuel economy. This manual provides detailed, professional-level repair and rebuild information, equivalent to factory service manuals, for DIY mechanics, professional technicians, and automotive repair shops. It thoroughly covers disassembly, assembly, component replacement, and servicing of internal parts such as clutch packs, solenoids, and the valve body. Crucially, it includes comprehensive diagnostic procedures, troubleshooting guides, electrical and hydraulic schematics, exploded views, and maintenance protocols, including fluid specifications and common wear points. This resource is designed to empower users to maintain and repair these transmissions with accuracy and confidence, ensuring optimal performance and longevity.