Wide shoes accentuate the effects of
impact conditions. Machines with single
grouser shoes are more susceptible to
higher impact effects than those with
lower profile or multi-grouser shoes.
Packing
Packing describes any condition where
underfoot material sticks to or packs between
moving undercarriage components. It has
two major effects. First, it can prevent mat-
ing parts from properly engaging each
other causing interference, high loads and
increased wear rates. The best examples of
this effect is sprocket teeth packing, or
packing between shoe and bushings, caus-
ing the teeth to engage the bushings under
interference.
The second major effect of packing is it
binds abrasive particles to moving compo-
nents thus increasing the wear rate. The
best example of this is a sand-clay mixture
packed around idlers, carrier and track
rollers causing constant abrasion when
these components turn. The result is
similar to a grinding or polishing wheel.
Parts subjected to this effect are usually
polished smooth.
Severe cases of packing will prevent the
rollers, particularly carrier rollers, from
turning. Then links must slide across roller
treads causing flat spots which are easily
recognizable.
Packing materials vary widely and extend
far beyond clay and mud that are normally
associated with the above effects. The fol-
lowing list of materials can result in one or
both of the major effects listed above.
Obviously, the moisture content of most of
these materials helps determine its sticki-
ness and its compactability. Many under-
foot conditions are composed of various
combinations of these materials and the
effect may be cumulative. Packing materi-
als fall into two categories; (A) those that
can usually be extruded (squeezed out)
from between the parts when wet and (B)
those which cannot be extruded with the
pressures and opening sizes normally avail-
able in track type machines.
Packing Materials
A Extrudable (when wet)
Sanitary Landfill (garbage)
Silt soils
Clay soils
Sandy soils
Snow and ice
Metallic ores (taconite)
Non-metallic ores (gypsum)
B Non-extrudable
Sanitary Landfill (garbage)
Branches, twigs and brush
Stones, rocks and gravel
Demolition debris
Sod-like materials
Generally, packing effects cannot be con-
trolled except by constant cleaning or
removal.
The most common modification to under-
carriage components or use of option attach-
ments involves providing Trapezoidal
openings for the packing type material to
extrude (squeeze) or fall out, thus reliev-
ing the pressure. These modifications or
attachments should only be used in the
presence of extrudable type materials.
(List A above)
1. Trapezoidal Openings in shoes.
Caterpillar recommends that track shoes
with trapezoidal openings be used in the
presence of extrudable type material
(see list A above). Track Shoes with
trapezoidal openings are available for
most models from Caterpillar. The pro-
cedure for dealers or users to cut trape-
zoidal openings in shoes is described in
Information release memo UC89-17
dated Oct. 4, 1989.
2. Roller guards should not be used in
packing type materials except when
rocks could enter between the rollers
and cause crushing damage. Roller
guards prevent most materials from
extruding or falling out and cause more
damage than they prevent.
22
UNDERFOOT CONDITIONS
General Information