Although Stewart-Warner was best known for speedometers, it also mass-produced things such as fuel pumps, heaters, horns, mirrors and spotlights. In addition, the company made Alemite lubricating equipment. And, its diverse product lines even extended beyond auto parts, including everything from refrigerators and scoreboards to radios and televisions.

Stewart-Warner’s large, castle-like headquarters on the North Side of Chicago (1826 W. Diversey) housed offices and production facilities (at its peak, the 1-million-square-foot facility employed 6,000 people). The massive six-story building, which featured a big clock tower, was a local landmark to generations of Chicagoans. Inside, workers stamped and machined thousands of tiny parts that were fed to assembly lines.

Mechanical speedometer dials were driven by a rotating cable attached to a set of gears in an automobile’s transmission. Metal and plastic parts typically consisted of gears, magnets, springs and shafts that were manually assembled. Dials were painted by hand and components were attached by screwdriving and riveting.

As automakers began to use more electronics in the 1970s, Stewart-Warner failed to keep up with the trend and slowly lost its way. The company was eventually sold to a British firm in the late 1980s and its distinctive factory was torn down in the early 1990s. However, the Stewart-Warner brand still exists today as a part of CentroMotion.

To view photos of Stewart-Warner’s assembly line and learn more about other factories that made Chicago a production powerhouse, see Made in Chicago: The Windy City’s Manufacturing Heritage.