A miniature gear drive, such as that used in clockworks, is disposed in one chamber of a housing having two chambers interconnected by a capillary channel. The chamber containing the gears is sealed except for the channel, and the entire assembly immersed in a lubricant liquid within a vacuum chamber. The vacuum chamber is evacuated and then the vacuum removed so that the lubricant completely fills both chambers of the housing. The assembly is removed from the vacuum chamber and heated whereby the liquid expands and a portion of the liquid escapes through an opening in the second housing chamber. The assembly is then cooled so that an air bubble is formed in the second housing chamber, and the second chamber is then sealed. The input power to the gear drive, and the output power therefrom are obtained by magnetic coupling through the housing. The air bubble permits expansion of the liquid within the housing due to temperature changes, but the capillary channel prevents this bubble from reaching the chamber containing the gear drive hence the gears are always completely immersed in the liquid.