Clarence Killebrew entered the construction machinery business with the J.D. Adams Manufacturing Company factory school in 1934. In 1940, he joined Frank G. Hough Company where he played a role in the development of the Payloader line.
In 1952, Killebrew joined Clark Equipment Company, where he was responsible for the design and production of a line of tractor shovels that became the nucleus of the company's Construction Machinery Division and the Michigan line. Throughout his career, he was a leader in broadening the global application of four-wheel drive tractor shovels (wheel loaders) and dozers.