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(211)
CHASSIS SUSPENSION
TROUBLE DI
AGNOSIS
6-13
..-- HIGH
Figure 6-
14-Tread
Block Heel a
nd
Toe
Wear
center and the outer edges of the tire tread.
This
saw-toothed
appearance, however, will be
exaggerated by urrderinflation, improper toe-in,
or both.
h. W
a vy
Tread Wear,
Flat
Spot s, and
Cupping
Many combinations of factors may cause the
types of tread wear listed here; therefore it is
never possible to say definitely that anyone
condition is the cause.
As stated above (subpar. g) a small amount
of irregular wear at the outer segments of tires
is a normal condition; however,
irregular
wear
extending toward center of tread is due to
wheel misalignment conditions which should
be
corrected. Careful
checking and adjustment
of all wh
eel
alignment factors (par. 6-29 and
6-30) will r
edu ce
such wear.
An
overinflated
tire tends to bounce instead
of keeping in contact with the road
surface.
On
t
urns
this bouncing produces scuffing and may
cause flat spots to
develop.
A tire that is statically unbalanced bounces
or hops on the road, causing
rapid
and uneven
tread
wear.
Uneven brake adj
ustment
or
grabbing
brakes
will
ca
use rapid and un
even
tread
wear.
Out of
round
bra ke dru ms w
ill
cause
flat sp
ots t
o
de-
velop on ti
r e t
reads.
Wabble
or
runout of a
t
ir e,
either
front or
rear, du
e
to bent wheel or to tire being
improp-
erly mounted
will
cause
uneven wear. The run-
out of wh
eel
and tire when rotated should not
exceed
lis"
at
side
of tire.
Looseness
of parts in the suspension
system
such as worn king pins or steering knuckle
bushings, loose wheel bearings, worn knuckle
support pivot pins or bushings,
inoperative
shock absorbers, and any excessive looseness
throughout t
he steering system all tend to al-
low the front wheels to kick around, and if any
of the wheel alignment factors
are
incorrect,
irregular spotty tire tread wear of one t
ype
or
another may result.
Regardless of the
original
cause of spotty
tread wear on either front
tire,
no alignment
or balance job, however perfect, can
prevent
future excessive wear of the
spots.
Once a front
tire acquires flat or cupped spots ext r a rapid
wear will continue, caused by the braking and
steering strains on the thinner and
weaker
sec-
tions of the
tread.
A thorough mechanical and alignment in-
spection, plus a check for
wheel
and
tire
unbal-
ance, should uncover the cause or causes of the
irregular wear. At the time of correction, how-
ever, the cupped tire should be interchanged
with a rear tire on which the tread runs
true.
The cupped
tire
will, to a
certain degree,
true
itself up on a rear wheel
because being
rigidly
mounted to the axle shaft it can only r
evolve,
absorbing first the driving and
then the
brak-
ing strain.
6-
10 FAULTY
SPRINGS
OR SHOCK
A
BSORBERS
a. Weak Springs
Measurement
of the t
rim dimension
wit h
springs installed is the only practical
method
of checking chassis
springs
that are r
eported
to be weak. See paragraph 6-17 fo
r checking
trim
dimension
of front springs and
paragraph
6-20 for rear
springs. The strength
of chassis
springs cannot be
det ermined
by
measu r ement
of the
free
length
when
removed from car , be-
cause springs of equal
strength under
rated
load
may
vary considerably in length
when
not
loaded.
b.
Weak
or Inoperative
Shock
Absorbers
Many shock absorbers
have been
replaced
and returned to the f
actory w
ith
the
r
eport
that
they were
wea k. When teste d with sp
ecial
factory
equ
ipment
very
f
ew of these
r
epl ac ed
units have been
foun d weak or
otherwise below
standard in
operation. This
in
dicates
that
these
sho
ck
absorbers
were needl essl y
r
eplaced
in an
attempt
t
o improve
riding
conditions
that
were
actually
standard, or that er r oneo us methods
were
used in judging the
operating
condition
of the units.
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