A dozer is designed to be a leveling machine.
Ideally, with the bade out front the dozer is pushing out a flat surface for the track to ride on. There are track rollers distributed under the center of the machine that are designed to take the weight. The rear sprocket provides the drive to turn the track chain and is a little higher than the track rollers. The track system is designed so that the chain under the sprocket is not in weight bearing contact with the ground relative to the rollers. When you put a winch on the back you add a lot of over hanging weight on the back of the dozer. Then when you pick up a log you add more weight. When you drag the log the front of the dozer wants to tip back. This
can put the track section under the sprocket in hard contact with the ground. And if it is rough ground it adds a hammering action. The bearings in the final drive that turn the sprockets are not designed to take that kind of punishment for very long.
You can see the shaft ends of rollers (covered by the rock guards) which are along the weight bearing portion of the track. And the sprocket which is higher.
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