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6-28
WHEEL BALANCE
CHASSIS SUSPENSION
(226)
llV
~
CENTERLINE OF
WEIGHT MASS
I
I
C
iO
1
I
No.1
No.2
No.3
No.4
Figure 6-34-Static and Dynamic Balance
By referring to figure 6-34, view No.1, it
can be seen that when a wheel and tire assem-
bly is in static balance, the sum of the weights
of sections "A" and "B" is equal to the sum of
the weights of sections
"
C" and "D"; or, in
other words, the weight is equally distributed
about the axis of rotation. View No. 2 is a
drawing of a wheel that is in static balance be-
cause the shaded heavy point "B" is balanced
by the shaded heavy point "C." However, it can
be seen that with reference to the center line,
section "A" is lighter in weight than section
"B," and that section "D" is lighter in weight
than section "C."
When we start to spin this wheel, as in view
No.3, the center line of the weight masses "B"
and "C" tries to get at right angles to the axis,
just as the weight on the string tried to get at
right angles to its axis of rotation (the hand).
This tendency to get at right angles exerts a
force on the wheel, as shown by the arrows.
This force, in turn, tends to move the center
line of the wheel and, in so doing, distorts the
axis of rotation.
When the wheel has turned 180
0
,
the forces
exert ed by the heavier sections
"
B" and "C"
now tend to move the center line of the wheel
in the opposite direction. In other words, the
wheel tries to rock
first
in one direction, then
in the other. The result of the movement of
these unbalanced forces causes the wheel to
wobble .or shimmy, and the condition becomes
more violent with increased speeds.
To correct this condition we must add weight
to sections "A" and "D," so they will be equal
to the weight of sections "B" and "C." Notice
that this addition of weight now
distributes the
total weight evenly about both the axis of
r
ot a-
tion and the center line of the wheel as seen
in
view No.4. Therefore, this wheel is now both
statically and dynamically balanced.
6-28 WHEEL AND TIRE BALANCING
PROCEDURE
a. Static Balancing
Static balancing is a simple procedure
and
can be done on any good
balancing
equipment
of either
t
he
vertical
or
horizontal
type.
If
such equipment is n
ot available, a simple
static balancing fixture
may
be
made from a
used
steering knuckle, hub,
and
bea r
ings.
Mount
the steering knuckle solidly on edge of bench
by means of
suitable
steel straps.
Remove
the
felt packing from hub, wash bearing free of
lubricant and adjust bearings so
that a
ver y
slight looseness may be felt. When a
wheel and
tire assembly is mounted in a vertical
position
on the fixture, the heavy side will go to the
bottom.
With any type of static balancing equipment
the first step is to locate the light spot on
the
wheel and tire assembly. Mark this spot
with
chalk and add sufficient weight at this
point t
o
exactly balance the assembly
staticall
y.
Wheel
balance weights having
metal clips for
attach-
ment t
o the
flan
ge of
wheel r
im
are listed in
V2,
1, 2,
and 3
ounce sizes under group
6.367
of the Master Parts List.
If
a single weight will balance the wheel,
one weight may be used.
If
more than one
weight is used, the weights should be distrib-
uted equally from the light point on the same
flange. See figure 6-35, views A, B, C.
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