Allis-Chalmers M7: The Abominable Snow Tractor
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Because of extremely harsh weather conditions, fewer than 1,000 people live in a county about the size of Rhode Island. Snow is on the ground most of four months at a depth of about 3 feet on the flat and much deeper in the mountains – the ideal location for someone with an Allis-Chalmers M7 snow tractor. Although our homes are in a small village, my brother and I can go out to garages where our snow tractors are stored, fire them up and strike out across a totally white world with nothing to impede our progress.
Claude has a log cabin built on an old mining claim far up in the mountains. The only way to reach it in the winter, with supplies necessary for an extended stay, is with the M7s. My sons and I once spent a week there during a “spring break” in late March. At lower elevations, it would have been spring. At high altitudes, though, winter remains in full swing in late March.
Military M7s had a canvas cab that covered two passengers (one seated behind the other). Idaho Fish & Game modified its M7s by creating larger, all-weather cabs. Several designs were created; all were wood-frame with a solid roof and doors that could be closed. No. 177 could transport five people with the driver in front and the other four sitting facing each other along the sides in the rear. A roof rack held the supplies we’d need for a week in the wilderness.
When launching into a world of deep snow and extremely cold temperatures, one must realize the intrinsic danger. That is especially true when children are involved. In an emergency, help is far off. We made the trip before cell phones were available, but cell phones don’t work in mountain valleys anyway. We committed our wellbeing to an extremely old military vehicle. It didn’t let us down.
A challenging transmission
Although Allis-Chalmers built the M7 snow tractors, the military required a Willys Jeep’s power train, simplifying parts and service. Thus the M7 has a Warner Gear T-84 3-speed transmission. A high-low auxiliary transmission doubled the number of gears available. Moving the M7 in almost any kind of snow other than hard crust takes a lot of power. Because of that, the transmission is extremely taxed. Ideally, the driver would have the transmission in low gear/high range and ground speed would be something like 12 to 15 mph.
Unfortunately, T-84 transmissions use brass thrust washers on the transmission cluster that runs low gear. The constant hard work necessary to move the tractor in the snow puts so much pressure on those thrust washers that they wear out quickly. When that happens, the cluster gear is allowed to move enough in the case to interfere with the other gears. That brings the snow tractor to a halt until the transmission can be removed and new thrust washers installed.