This workshop manual covers Mercury MerCruiser TR Stern Drive Units manufactured between 1978 and 1993. These stern drive units are engineered for marine applications, providing reliable propulsion and steering for a wide range of watercraft. Designed to integrate with engine displacements from 2.5L to 7.4L, they offer power output ranging from 120 HP to 330 HP, ensuring robust performance on the water. The transmission features forward, neutral, and reverse gears, with variable drive ratios tailored to specific model and engine configurations, embodying Mercury MerCruiser's commitment to durable marine engineering. This comprehensive service manual is intended for repair and maintenance of the Mercury MerCruiser TR Stern Drive Units. It details essential procedures, including lower unit gear oil changes, recommended lubricant types, trim system fluid capacities, and cooling system configurations. Guidance is provided on anode replacement intervals and propeller lubrication, crucial for maintaining the longevity and operational efficiency of the stern drive. This manual serves as an indispensable resource for owners, technicians, and mechanics, offering the technical specifications and step-by-step instructions necessary for effective upkeep and repair.