Eimco Power Horses: The Horse that Walks Like a Tractor
Detail from the original Bonham patent, filed June 26, 1937 and issued April 16, 1940.
The 'Let's Talk Rusty Iron' column in the June 1999 issue of Farm Collector was about tractors that could be driven with reins from a trailed implement. That brought a response from Harold Probasco of Huntsville, Utah, who not only owns two rare Eimco Power Horses, but has one of the very early models which is probably the prototype that the Bonham Brothers put together in 1937.
The story of the Eimco Power Horse has been told before, but briefly, here's how it began: Utah residents Bond and Bert Bonham invented a small, four-wheel drive tractor during the mid-19305. They applied for a patent in June 1937 and, though the patent wasn't granted until April 16, 1940, the Utah Construction Company of Ogden, Utah, began to build the machine in about 1937.
Mr. Probasco's early model has a Hercules IXB 3 1/2-inch bore by 4-inch stroke engine. It appears that the Hercules power plant was used for a year or two, until the Eimco Corporation of Salt Lake City, Utah, took over building the machine. After that, Allis-Chalmers model B engine skid units were used. This accounts for the definite resemblance of the Power Horse to an Allis-Chalmers model B, although the Eimco-built tractors were painted all copper (with the later version having a tan hood and wheels).
The Power Horse is lever-controlled and, with reins attached to the levers, can be driven from the seat of a trailed implement in much the same way as a team of horses is driven. The owner's manual for the Eimco Power Horse gives the following procedure for driving the machine: First, the engine is started and one of four transmission speeds is selected, using the master clutch lever to disengage the transmission. Then, after making sure the two control levers are locked in their center, or neutral position, the master clutch is engaged.
After mounting the seat of the implement, the driver gives the reins a slight tug, releasing the neutral lock. Both lines are then freed, so the control levers assume their spring-loaded forward (or run) position, at which time the Power Horse moves forward.
When one control lever is pulled to the rear and the other is left in its forward position, the Power Horse turns toward the side upon which the rein is pulled. The sharpness of the turn depends upon how far the levers are pulled back, or allowed to go forward, if in reverse. Steering is accomplished by the steering clutch disengaging power to both wheels on the turning side. If one lever is released, and the other is pulled all the way to the rear, the wheels on each side will turn in opposite directions, and the tractor will spin around in its own tracks.
To reverse, the control levers are pulled all the way back. This causes the steering clutch on each side to disengage, while the reversing band on each side engages and, through a set of planetary gears, the Power Horse moves backward at half the corresponding forward speed. The tractor can be steered in reverse by releasing the pressure on the rein toward the desired direction of turn, and holding back on the other rein.
To stop, both levers are pulled simultaneously to the middle position, where they lock into neutral and remain until a light pull on either line instantly releases the neutral lock, allowing the machine to move forward or back, depending on how the reins are positioned.
Options available for the later model Power Horses included a PTO and belt pulley, as well as electric start and lights, power hoist, foot-operated hydraulic brakes, and a buck-rake hitch. While the Power Horse was primarily intended to use horse-drawn machinery, the manual shows a rear-mounted mower that was adapted from the International Harvester 16A or 25A PTO mowers. A mounted, two-way plow was available, but no manufacturer is listed. Photos of these two mounted implements show the operator sitting on a pan-type seat mounted over the tractor's rear axle.
No one knows how many Power Horse tractors were built before manufacturing was shut down for World War II, but there probably weren't more than 300. Allis-Chalmers seems to have acquired rights to the design and experimented with a four-wheel drive tractor through the war's end. There is some evidence that Bert Bonham went to work for A-C, and was involved in the project. Allis-Chalmers built and tested six prototype 'Model H' machines, but dropped the idea sometime in 1945. The problem A-C had with the design was the fact that, in order to turn, power to the inside wheels was interrupted, and the outside wheels didn't have enough traction to pull the load through the entire turn.
Harold Probasco, assisted by his grandson, Mark, collects all sorts of antiques. He has an old log cabin that's restored and filled with the appropriate antiques, as well as a restored one-room school house. The Probasco collection includes some rare gas engines, such as a Fairbanks Jack Of All Trades, a 1906 Western, a 1915 Detroit 6 hp, and a 12 hp hopper-cooled 1906 International Famous. Beside the three Power Horses, Harold has a McCormick-Deering 10-20, an Allis-Chalmers B, a Cockshutt 30, and an early Oliver 88. Rounding out the tractor collection is a one-of-a-kind 'Farmwell F-6 Economy Dearing.' Harold put this gem together using a Farmall F-12 chassis, and a 6 hp Economy engine.
A few years ago, a visitor was looking at Harold's Power Horse tractors, and said, 'I think I have one of these, but it doesn't look anything like yours.' Harold checked it out and found the prototype, complete with wheels, controls and Hercules engine, but missing the hood and radiator. The owner was about to take it to a junkyard, so Harold, trying not to show his excitement, made an offer, which was accepted. Harold checked with Bert Bonham, who is pretty sure the machine is the original prototype he and his brother built in 1937. The tractor was taken to Nelson Inter-Mountain Crane Services for restoration. Photos of the early machine reveal that the hood and grill were a little different, but Harold had the restorer make the hood, side panels and radiator look the same as the original patent drawing. FC
Ever since his days as a boy on a farm in western Pennsylvania, Sam Moore has been interested in tractors, trucks and machinery. Now a resident of Salem, Ohio, he collects antique tractors, implements and related items.