Written by Larry Gay
Through the years, tractor manufacturers kept expanding the number of forward speeds for farm tractors to enable the farmer to select a more optimum speed for the operation being performed. By the mid-1960s, many tractors provided 12 forward speeds and some as many as 16 or 18. Then in the summer of 1967, International Harvester introduced a hydrostatic drive for its 656 tractor which provided an infinite number of forward speeds between 0 and 20 mph. The 656 was also built with a gear-type transmission, so the hydrostatic version was labeled with the word “Hydro” on each side of the hood.
The hydrostatic drive used a piston-type hydraulic pump, which was driven by the tractor’s engine, to pump oil to the piston-type hydraulic motor. The hydraulic motor was connected to the input shaft of a 2-speed transmission which provided forward speeds between 0 and 8 mph in the low range and 0 and 20 mph in the high range. A single lever on the left side of the dash was used to control the volume of oil being pumped which in turn controlled the speed of the tractor. Moving the lever farther forward increased the forward speed and pulling the lever back from its neutral position provided speeds up to 9 mph in reverse.
The 656 Hydro tractor did not have a clutch, but a foot pedal was provided to assist the operator when hitching to implements and could be used for emergency stops. The customary two brake pedals were provided for turning and could also be used to stop the tractor. The hydrostatic drive was very convenient for loader work as it eliminated the need for clutching and shifting gears as the tractor moved forward and backward. It also enabled the operator to maintain the exact desired speed for planting and applying chemicals. PTO work was easier because the travel speed could be easily adjusted to match the crop conditions.
The 656 Hydro was available in the Farmall (row crop) and International (utility) configurations.
It was powered by an International 6-cylinder, 263-cubic-inch gasoline engine or a 6-cylinder, 281-cubic-inch diesel engine. Both versions produced about 66 PTO horsepower during their Nebraska tests.
By 1970 International Harvester had four models of farm tractors with a hydrostatic drive -- the 544 Hydro, the 656 Hydro, the 826 Hydro, and the 1026 Hydro. Today hydrostatic transmissions are popular for lawn tractors and compact tractors and the New Holland TV145 bi-directional tractor is equipped with a hydrostatic transmission.
Larry Gay is the author of four farm tractor books and the “Machinery Milestones” articles in Heritage Iron magazine. To learn more about this magazine which focuses on the 1960-1985 era, go to heritageiron.com or call 1-800-552-6085.