The Unique Allis-Chalmers WD Tractor
Written by Larry Gay
Allis-Chalmers introduced its WD tractor in mid-1948 as the replacement for the WC model. Although the WD retained the 4-cylinder, 201-cubic-inch Allis-Chalmers gasoline engine, design improvements and a 100 rpm increase in the rated engine speed to 1,400 rpm resulted in 34.6 belt horsepower instead of 29.9 for the WC. The styling remained similar to that introduced for the WC for the 1939 model year and the driver remained positioned in-line with the right frame member. However, the brakes were now operated by two pedals instead of hand levers.
The first of three unique features for the WD tractor was the two-clutch system in which a hand lever operated a clutch located between the PTO power train and the transmission. Moving the hand lever forward stopped the travel of the tractor, but didn’t stop the PTO or hydraulic system. This was ideal for the Allis-Chalmers Roto-Baler which required the forward travel to stop, but not the PTO, while the small round bale was being wrapped and ejected. This hand-operated clutch could also be “slipped” to reduce the travel speed when a harvesting machine encountered a heavy spot of crop. The regular clutch was operated by a foot pedal and it stopped both the travel and PTO.
The second unique feature for the WD model was the hydraulic system. The Traction Booster system used a single attaching point under the tractor to pull the rear-mounted implements and two lift arms powered by two hydraulic cylinders to raise and lower the implements. This system provided weight transfer to the rear wheels of the tractor for increased traction. A one-way hydraulic cylinder was available for use with pull-type implements. Since the system operated at over 3,000 psi, the hydraulic cylinders were small diameter, low volume units.
The third unique feature was the Power-Shift rear wheels which permitted adjusting the rear wheel tread to one of five positions by using the power of the tractor instead of a jack. The rims of the rear wheels were equipped with diagonal rails and the center discs of the wheels were attached to the rails with clamps. Loosening the clamps and placing a stop on the rails enabled the operator to use the power of the engine to “spin” the rear wheel to the desired position. The narrowest position was used to reduce side draft when plowing and the wider positions matched the row width when cultivating.
The Allis-Chalmers WD tractor was produced from 1948 to 1953 when it was replaced by the WD45 model with more power. However the WD45 retained the three unique features introduced by the WD.
Larry Gay is the author of four tractor books published by the American Society of Agricultural and Biological Engineers including Farm Tractors 1975-1995 and Farm Tractors 1995-2005. The four books may be obtained from ASABE by calling 800-695-2723.