18
VIBRATION
General Information
Track-Excited Vibration
Track-excited vibration is the most widely
encountered vibration on track-type ma-
chines. However, it is not understood by
many persons who work with these ma-
chines. As the machine moves, each link,
as part of an endless rail, makes contact
with two curved surfaces — each with a
different radius. These are the idler and the
track rollers. Contact between the links,
idler and rollers results in wearing of the
links’ once-straight surface. The contact
between the idler and the link creates a
worn radius in the center of the link simi-
lar to that of the idler.
The track rollers have a similar effect on
the ends of the links, which are narrowed
to permit them to overlap where they are
connected together. Because this overlap
isn’t 100 percent, the greatest amount of
wear is near the ends of the links, and the
size of the worn area has a radius similar
to that of the track rollers. As a result of
this wear, a scallop pattern is formed on the
surface of each track link. (See page 30).
This type of link wear can be accelerated by
three factors — abrasiveness and moisture
content of the soil, machine weight and
travel speed and underfoot conditions.
Rough underfoot conditions can place
higher loads at a given point on a link. It is
possible, on rocky or rough terrain, to have
a higher load on a link on one side of the
machine than on the other side. Although
rough terrain can accelerate wear, it is
sometimes possible that track-excited vibra-
tion will go unnoticed on rough terrain, yet
be apparent when the machine is working
on a smooth surface.
Along with the depth of scallop, the
scallop-roller spacing relationship is what
determines how smoothly the machine
will travel on the links. If the spacing of
the track rollers and scallops are uneven,
so that some of the rollers are on the high
points of the links while others are over
the low points, the machine will move
across the scallops smoothly. However, if
the spacing is the same, the rollers will rise
and fall in unison with each scallop as they
pass over the links, thus creating vibration.
Two factors, machine speed and the depth
of the scallops, affect the amount of vibra-
tion. The speed of the machine determines
the frequency of the vibration while the
depth of the scallops controls the ampli-
tude of the vibration. In addition, natural
frequencies, which occur in all structures,
can respond to the vibration. Because of
this response, it is possible for certain
parts of a machine, such as the roll-over
protection structure, sheet metal compo-
nents, or, sometimes, the whole machine,
to respond to the initial frequency and
begin vibrating.
The vibration can be reduced by replacing
deteriorated isolation mounts where neces-
sary, replacing any broken or missing fas-
teners and by generally keeping the machine
in good repair. A change in operating speed
or technique, or a change of counterweights
or attachments may reduce the effect.
Testing and Adjusting Front
Idler Position and Machine
Balance (D4H to D7R)
Operator complaints of ride arise when a
machine is vibrating more than normal.
Abnormal vibration is generally caused by
an idler that is lower than the track rollers,
a machine that is not balanced, or scal-
loped track links.
Special Instruction entitled “Adjustment of
the Position of the Front Idlers and the
Balance of the Machine for Improved Ride or
Improved Fine Dozing,” REHS0862-02, dated
June 01, 2001, covers the following topics:
• Correct Track Installation
• Measuring Grouser Rise Height
• Verify the Installation of the Correct Idlers
• Measuring the Depth of the Link Scallop
• Shim Charts for Idlers
• Measuring the Height of the Front
Idler Tread