Allis-Chalmers M7: The Abominable Snow Tractor

Vintage vehicle still a hard-working winter warrior

Sons Curtis and Forrest with their dad (Clell Ballard) on an outing in M7 no. 177

Sons Curtis and Forrest with their dad (Clell Ballard) on an outing in M7 no. 177. Skis and a toboggan are included for recreation, but also as back-up transportation in case of a major mechanical breakdown.

courtesy Clell Ballard

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Farm Collector recently ran an article about an impressive restoartion of a rare 1944 Allis-Chalmers M7 military snow tractor.

(Read “ Allis-Chalmers M7 Restoration ,” by Bill Vossler, November 2009.)

With a production run of just 291 (all in 1944), very few M7s are still in existence. Even dedicated collectors who would like to have one of every tractor AC produced have found that obtaining an M7 is next to impossible.

Search for a snow tractor

As strange as it may seem, at least a couple of those elusive tractors are still doing what they were designed to do more than 65 years after they were built: provide transportation in deep snow where other vehicles never go.

My brother, Claude, and I both own M7s and use them in the high mountains near the totally unsettled area of central Idaho. Claude’s first exposure to the snow tractor was in the early 1950s when, as a Boy Scout, he and his fellow Scouts were transported into the rugged Sawtooth Mountains by Idaho Fish & Game Department officers. The wintertime exercise trained the Scouts in survival skills in primitive conditions. At that time the vehicles (which had been obtained from U.S. Army surplus) were fairly new and had proven themselves with the department for use on extended trips far from civilization. In deep snow (depths of 10 feet were not uncommon) and extreme temperatures (dipping to 25 below zero), the M7s were depended on without reservation.

In 1978, after the Fish & Game Department retired the vehicles, Claude traveled almost 1,000 miles round-trip to buy his M7 (no. 255). He also got a large number of spare parts, including two extra tracks – a real plus, as there is no known source for parts. Since so few machines were built, the military purchased only the minimum number of parts needed.

I stumbled on to an M7 (another ex-Fish & Game vehicle) at a bankruptcy auction a few years later in an area where it rarely snows. Although my financial resources were very limited, I managed to buy the M7 (no. 177) because the auction was held on an August afternoon when the temperature was near 90 degrees. Since they didn’t live in snow country like I did, the other bidders weren’t very motivated. Later in the auction another M7 (no. 195) was auctioned off. Its condition could only be described as “a hulk.” I bought it, too, for the princely sum of $40.

Winter warrior

We live in an isolated mountain valley at 5,000 feet elevation with low mountains on the south and peaks reaching over 10,000 feet on the north.

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.

Experienced operators avoid that disastrous problem by traveling in high gear/low range in most snow conditions, making forward movement much slower, ranging from 8 to 10 mph. Inside the vehicle a loud roar is heard as the engine labors, running at rpms as high as is deemed prudent. Outside, where the mechanical noise is less noticeable, onlookers get the impression that an M7 is a smooth, fairly quiet vehicle.

There is another danger for M7 operators to be aware of. In all snow conditions, as the front drive sprocket pulls the track, the top is really tight and there is a certain amount of slack on the bottom. In some wet snow conditions, snow gets packed between the drive wheels and the rubber rails they run on. Every so often, a wise operator stops and checks for that condition. Should it be ignored, the stress can become so extreme that the cables holding the track together can break and the snow tractor is rendered immobile until spring arrives and a new track can be transported to the break-down site.

Simple pleasures

At the slow speeds we traveled, it took several hours to reach the mountain cabin, which we discovered almost completely covered with snow. Since the short winter day was nearly over, we quickly lit gas lamps and fired up the fireplace and wood-burning cook stove. After several hours we were toasty warm: The deep snow around the cabin insulated us from the cold.

During the days the kids skied, rode the toboggan and read. I functioned as chief cook. Free time was used to chop wood and carry snow to be melted for water. Too soon our reverie came to an end. We found the return trip easier and faster because it was downhill and we were traveling in the track we made coming up. We put our trust in a 1944 Allis-Chalmers M7 snow tractor and it performed with flying colors. FC