You have to be really careful trying to move railroad cars with equipment that was not designed to do this. I have seen two farm tractors destroyed this way. They were trying to move loaded covered hoppers by tying a big hawser rope to a corner of the car and pulling it with the tractor (bends the car pretty bad, too). In the first instance, the drive wheels on one side of the tractor broke their centers out, dumping the tractor. In the second instance, the train crew failed to notice a tractor was tied to a cut of cars. The tractor was dragged alongside the cars, destroying it a bit at a time. By the time it was discovered, there was not much left of the tractor. In this case, the cars had been released by the elevator (which constitutes an order to pull), but the train crew is still responsible to make sure the cars are clear to pull. I have also seen this same elevator release cars to pull while a grain inspector was still walking the tops of the cars taking samples.
I also saw a front end loader shortened up by about two feet. The operator was trying to drag a cut of empty covered hoppers down a grade to couple to a cut of loads. He discovered the brakes on a front end loader cannot stop five or six 30-ton empty railcars. He was straddling the rails at the time. The empties forced the loader into the loads, sandwiching it. The loader bowed up in the middle (with the driver still in the cab). He could easily have gotten killed, but was unharmed. The loader was toast after that.
People moving these cars fail to appreciate the weight of even empty cars. In my opinion, any device used to drag cars around needs to be able to put air into the cars so brakes can be dumped immediately to avoid an accident. If you use something other than a wheeled vehicle, use a cable system with a very strong drum brake.