Eimco tractors could be driven by reins

Sam Moore and Harold Probasco
Harold Probasco (left) and columnist Sam Moore are riding on a cart behind the tractor that Harold believes is the prototype built in 1937 by the Bonham brothers of Salt Lake City, Utah. (Darrin Christensen photo)

I’ve never told the story of my 2002 visit to Harold Probasco of Huntsville, Utah. I’d written a magazine article about tractors that could be driven with reins from a trailed implement and that brought a response from Harold, who not only owned an Eimco Power Horse, but also had a very early model which is probably the prototype that the Bonham Brothers put together in 1937.

When I visited, Howard showed me the two tractors and very generously let me drive them as well.

In the beginning

Sam Moore and Harold Probasco
In this photo, Harold Probasco (left) and columnist Sam Moore are on a light wagon behind an Eimco Power Horse. These rein-driven tractors are very easy to drive, although Moore didn’t try to back one up.

The story of the Eimco Power Horse has been told before, but briefly, here’s how it began.
Utah residents Bond and Albert (Bert) Bonham invented a small, four-wheel drive tractor during the mid-1930s. They applied for a patent in June of 1937 and, although the patent wasn’t granted until April 16th, 1940, the Utah Construction Company of Ogden began to build the machine about 1937.

Mr. Probasco’s early model has a Hercules IXB, 3 1/2-inch bore by 4-inch stroke engine, and it appears the Hercules power plant was used for a year or two, until the Eimco Corporation, of Salt Lake City, 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 some Eimco-built tractors were painted all copper color while others had a copper chassis with tan hoods 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 a team of horses is driven.

Getting it started

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 reins are given a slight tug, which releases the neutral lock. Both lines are then released 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 side toward which the turn is to be made.

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 there until a light pull on either line will instantly release the neutral lock, allowing the machine to again move forward.


Options available for the later model Power Horses included a PTO and belt pulley, as well as electric starting and lights, power hoist, foot-operated hydraulic brakes, and a sweep-rake hitch.

While the Power Horse was primarily intended to pull horse-drawn machinery, the manual pictures a rear-mounted mower that was adapted from the International Harvester 16A or 25A PTO mowers. A mounted, two-way plow was also available, but no manufacturer is listed. Photos of these two mounted implements in use show the operator sitting on a pan-type seat mounted over the tractor’s rear axle.

How many exist

No one knows how many Power Horse tractors were built before manufacturing was shut down by World War II, but there probably were less than 1,000.

Allis-Chalmers may have acquired rights to the design and experimented with a four-wheel drive tractor called the Model H. Allis-Chalmers built and tested six prototypes, but dropped the idea in 1945. There is also evidence that Bert Bonham went to work for A-C and was involved in the project.


Harold Probasco, assisted by his grandson Mark, collects all sorts of antiques. On his property is a restored log cabin that’s filled with the appropriate antiques, as well as a restored one-room schoolhouse.

The Probasco collection included in 2002 some rare gas engines, such as a Fairbanks Jack of All Trades, A 1906 Western, a 1915 Detroit 6HP, and a 12 horse, hopper cooled 1906 International Famous. Besides the Power Horse tractors, there was a McCormick-Deering 10-20, Allis-Chalmers B, Cockshutt 30, and an early Oliver 88. Harold also put together a one-of-a-kind hybrid, using a Farmall F-12 chassis and a 6HP Economy engine that he called the Farmwell F-6 Economy Dearing.

Thrilling find

A good many years ago, a visitor was looking at Mr. Probasco’s Eimco tractors, and said, “I think I have one of those, but maybe not, because it doesn’t look anything like yours.”
Harold checked it out and found the old prototype, complete with wheels, controls and Hercules engine, but missing the hood and radiator. The owner was just about to take the thing to a junk yard, so Harold, trying not to show his excitement, made an offer, which was accepted.

Harold checked with Bert Bonham who was pretty sure the machine is the original prototype he and his brother built in 1937. The tractor was taken to Nelson Inter-Mountain Crane Service, where the restoration was completed.

Photos of the early machines 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.

Harold had a sale a couple of years ago and, as far as I know, got rid of most of his stuff.


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Sam Moore grew up on a family farm in Western Pennsylvania during the late 1930s and the 1940s. Although he left the farm in 1953, it never left him. He now lives near Salem, where he tinkers with a few old tractors, collects old farm literature, and writes about old machinery, farming practices and personal experiences for Farm and Dairy, as well as Farm Collector and Rural Heritage magazines. He has published one book about farm machinery, titled Implements for Farming with Horses and Mules.



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