Abstract: A locking mechanism for locking a tilt frame of a hoist to a vehicle frame comprises a semi-annular ring connected in axial alignment to the hub of a hoist lift arm. The ring is adapted to receive a pin connected to the vehicle frame. An opening is formed in the ring and is sized to permit the pin to pass therethrough. When the lift arm is advanced to a retracted position relative to the vehicle frame the opening is positioned below the pin, such that the tilt frame may be pivoted relative to the base frame. When the lift arm is pivoted out of the retracted position to load and unload a container, the ring extends in overlapping position below the pin to prevent the tilt frame from pivoting relative to the base frame.