Written by Larry Gay
The first gasoline traction engines were designed to provide belt power for threshing machines. A drawbar was provided, but was only used to pull the threshing machine between farms or similar light work. In 1903, the Hart-Parr Company equipped three of its 22-40 model gasoline traction engines with an experimental heavy-duty differential which the company described as a “plow gear” for pulling a plow. By 1906, all of the 22-40 tractors were built with the plow gear. Soon all tractors were built to provide two sources of power, belt and drawbar.
International Harvester started production of the International 8-16 tractor with a small preproduction run in 1917 and regular production in 1918. It was a 2-plow tractor with a vertical 4-cylinder, kerosene-burning engine and a 3-speed transmission. The radiator was located in the middle of the tractor which permitted the tractor to be equipped with a downward-sloping hood. The first commercially successful power take-off (PTO) shaft attachment in the U.S. was made available for the 8-16 in 1919. Little information is available about this PTO, but in one photograph the PTO shaft appears to be located under the tractor’s rear axle and to the right of the tractor centerline. Now there was a third way to transmit tractor power. International Harvester emphasized this by advertising its later 10-20 and 15-30 models as “triple-power tractors.”
Grain binders, corn binders, and corn pickers had been driven by a large ground-engaging wheel, but the PTO soon became the preferred method of driving these machines. As a result, most of the major tractor manufacturers began offering a PTO. One exception was the Fordson, but a component manufacturer soon made a PTO attachment for the Fordson. However, by 1926 there were seven sizes of PTO shafts on tractors, located from 32 inches ahead of the drawbar hitch pin to 13 inches behind the hitch pin. The PTO for the Fordson extended under the tractor’s right rear axle and the PTO for the John Deere D extended over the left rear axle.
In April 1927, the American Society of Agricultural Engineers (ASAE) issued a PTO standard which described the size and type of shaft, the speed and direction of rotation, and its location relative to the drawbar. Revisions to the standard were made in July 1928, March 1931, and August 1941 to reduce some of the variations in the original standard. This ASAE standard resulted in a 540-rpm, 1.38-inch diameter shaft with six splines, located on the tractor’s centerline, and 14 inches ahead of the drawbar pin hole.
Larry Gay is the author of four tractor books published by the American Society of Agricultural and Biological Engineers, including Farm Tractors 1995-2005. This book may be obtained from ASABE at 800-695-2723 or asabe.org, click publications and then click history books.