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6-14
TROUBLE DIAGNOSIS
CHASSIS SUSPENSION
(
2 12 )
Before attempting to test shock absorbers
make sure that all attaching bolts are tight and
that the un
its
are filled with specified fluid
(par.
6-23) . Tires
should be uniformly inflated
to
specified pressure (par.
6-8
)
,
The chassis
should
be
well lubricated to make sure that
suspension parts are free
moving.
Test each front and rear shock absorber in
turn by quickly pushing down and then lifting
up on the end of car bumper adjacent to the
unit being checked. Use the same force as near
as possible on each test, and note the amount
of resistance provided by the sho
ck
absorber
on compression and rebound. A little practice
on another car of the same model which has
satisfactory
ride
control will aid in judging the
amount of resistance that should exist.
Both front shock absorbers should provide
the same feeling of resistance and both rear
shock absorbers should do
likewise.
Any no-
ticeable variation between right and left shock
absorbers indicates that one unit is not oper-
ating normally. Little or no resistance on com-
pression or rebound indicates air in shock ab-
sorbers, internal leakage due to wear, or that
the valve is held open by dirt. Excessive resist-
ance indicates that bleeder hole in valve is
plugged with dirt.
If
there is any doubt about the action of a
shock absorber after testing as described above,
disconnect shock absorber arm at the outer end.
Quickly move the arm up and down through
complete range. There should be no free
move-
ment in the arm, and the force required to
move arm up and down should be almost equal
but with
slightly
greater resistance on the up-
ward movement. On the front shock absorbers
the upward movement is compression and on
the rear absorbers it is rebound.
Lack of resistance t
o
movement of the arm
indicates air in shock absorber, internal leak-
age due to wear, or
that
the valve is held
open
by
dirt.
Excessive
resistance
indicates that
bleeder
hole in valve is
plugged
wit h dirt. Air
may be worked out of a shock absor ber
by
re-
moving filler cap and moving
t
he
a
r m up and
down through full range and ad
ding fluid as de-
scribed in paragraph
6-23.
If
a valve
is
plugged
)1'
held open by
di
r t ,
or internal leakage due
to
wear
exists, the shock absorber must be
removed for
replacement
of valve or shock
absorber assembly
(par. 6-24) .
In either of
the tests
gi
ven
abo
ve, the
amount
rf force that can be applied is not
sufficient
to
ipen a valve against its spr ing pressure
; there-
fore these tests only
check-
the flow of fluid
through the valve bleeder hole as well as any
leakage due to a valve being held open or due
to internal wear of piston and
cylinder.
Since
it is unlikely that the valve springs will weaken
in service, it may be assumed that the shock
absorber action is normal if it operates satis-
factorily in the tests given
above.
6-11 IMPROPER STEERING ACTION
Steering action is dependent upon the chas-
sis suspension members as well as the steering
gear assembly and tie rods. Improper steering
actions which are most likely to be caused by
chassis suspension are covered in this para-
graph, while conditions most likely to be
caused
by the steering gear assembly or tie rods are
covered in paragraph 7-4.
a. Car Pulls or Leads to One Side
(1) High crowned roads.
(2) Low or uneven tire pressure
(par.
6-8).
(3) Front tires of unequal diameter due to
wear.
(4) Brakes dragging on one side
(par.
8-15).
(5) Shock absorbers low in fluid or inoper-
ative (par. 6-23 and 6-10).
(6) Incorrect caster,
camber,
or toe of front
wheels
(par.
6-30).
(7) Frame bent or broken (par. 9-2)
.
b. Steering Affected by Application
of Brakes
(1)
Low or uneven tire
pressure (par.
6-8).
(2) Front tires of unequal diameter due to
wear.
(3)
Brakes incorrectly
or
unevenly
ad
j
usted.
Dirt or grease on lining
(par.
8-15)
.
(4)
Incorrect
or uneven caster or bent
steer-
ing knuckle
(par.
6-30).
c. Car Wander or Lack of Steering Stability
(1)
Heavy cross wind.
(2) Type of road surface.
(3)
Low or uneven tire
pressure
(par.
6-8)
.
(4) Wheels toe out in straight ahead posi-
tion
(par. 6-30).
(5)
Incorrect
or
uneven
cast er or
camber
(par. 6-30) .
(6)
Steering gear
or t
ie r
ods
adjusted
too
loose or
worn,
or
adj ust ed too tight (p
ar . 7-4
)
.
(7)
Steering knuckle
bushings or king pins
worn
(par. 6-15) .
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