Page 158 - Moving the Earth_ The Workbook of Excavation

ROCK, SOIL, AND MUD

3.52 THE WORK

Wheeled Equipment. Rubber tires on vehicles are not as apt to freeze down or together, as the
flexibility of the tires prevents the ice from holding them effectively, and the rotating parts are
ordinarily not as close to the fixed parts. If such freezing does occur, the same means may be used
to thaw it, except that the rubber must be protected from heat.
The parts most vulnerable to freezing are the brakes, and here water will do as badly as mud. If
the vehicle is used in very wet or slushy conditions, then allowed to stand in freezing temperatures,
a film of ice will bind the brake linings to the drums. Driving back and forth on a dry stretch of
road, even if only a few yards long, with the brakes applied, for a few minutes before parking, will
usually dry them out again enough to prevent this trouble.
Frozen brakes may be loosened by rocking the car back and forth with its own power, or can
be thawed with hot water or flame.

JUMPING THE TRACK

A weakness of tracked vehicles is the possibility of going off the track. When this happens, it may
mean that the track is in a heap alongside the machine, the track wheels are resting on the ground; but
more often it means that the track rails are not engaging the wheel flanges properly, being displaced
to either side, and contacting the inner surface of the track shoe. Operation in this condition soon
leads to the complete separation of machine and track.
Jumping or running off the track occurs most often during sharp turns on uneven ground, and
is likely to indicate that tracks are too loose or have a broken link, or track and wheel flanges are
worn, or that wheels are out of line. It is usually accompanied by a snapping or grinding noise, and
if suspected, the machine should be stopped immediately and inspected, as every inch of movement
makes it harder to get back on the track.
If the track is off the truck rollers only, it will usually swing back into place if the track is
raised off the ground, by running the bull wheel or idler onto a log or other lift, or by jacking. If
the bull wheel is on hard ground, forcing down a hydraulic dozer blade will often raise the track
sufficiently.
The principle involved in getting a track back on a bull wheel or idler is similar to that of
installing a tight fan belt on a car. It cannot be pulled or pried enough to stretch it over the flange of
the pulley; but if it is held in one end of its place in the pulley, and the pulley turned, the wedging
action will stretch the belt over the flange, and the part of the belt already in the groove will draw
the rest of it in.
Similarly, with the track it is a problem of getting part of the track in line with the flange, and
turning the wheel to draw it on. If the track is partially on the wheel, simply turning it in the proper
direction does the job. If it is off the flange completely, it may have to be pried into line with a
crowbar, jack, or chain, and the track adjustment will usually have to be loosened as well.
If the track is off the upper part of the bull wheel, but still engaged with even one tooth at the
bottom, and with the truck rollers, the machine should be moved forward slowly. The sprocket
teeth will mesh properly with track appearing from beneath the rear truck roller, and will carry the
wrongly meshed section overhead into the slack upper section, where it will be straightened out by
the support roller. If the upper part of the bull wheel is correctly engaged, and the lower section
off, the track will work into place if the machine is reversed. However, it might be necessary to
pry with a crowbar to prevent the track from jumping off the rear roller.
If the track is entirely off the bull wheel flange, but still meshed with the truck rollers, the machine
should be moved forward. The bull wheel will roll onto track held correctly by the truck rollers,
and, perhaps with the aid of vigorous prying, should mesh with it and pass this correct meshing
up around itself. If the track is also off one or more truck rollers, the tractor should be backed so
that the bull teeth can mesh with track held correctly by the support rollers. This may require more
prying, or a pull in the correct side direction from another power source, or if the disabled
machine is a shovel, from a line to its boom.
Should the track be off at the idler, the above methods are still good, with directions of travel
reversed. If the track is tight, it may be loosened to facilitate crossing the wheel flanges. If the
track is off the support roller, it usually can be replaced by lifting with a crowbar.