Chevrolet 1980 Light Duty Truck Service Manual page 276

3C-8 FRONT SUSPENSION
Check Vehicle Ride and Handling
After completing previous checks, ride vehicle with
owner to determine if problem has been corrected or to
definitely establish type of problem that still exists. If
problem still exists (poor handling, bottoming, noise, ride
sway, etc.), proceed.
Inspecting and Testing the Shocks
Three procedures are included in this step. Thet are (a)
Bounce Test, (b) Inspecting Shock Mountings for Noise
(Looseness) and (c) Manually Operating Shocks to
Determine if Shocks are Weak, Leaking Hydraulic Fluid,
and/or if Shocks have an Internal Noise Condition.
SIMP Test procedures (b) and (c) require vehicle to be
on a hoist that supports wheels or rear axle housing and
front lower control arms.
Bounce Test
This is only a comparison type test to help locate the
suspected shock or noise condition before proceeding.
Test each front and rear shock by bouncing each corner
of the vehicle. This can usually be done by lifting up and
pushing down on the end of the bumper near each corner
of the vehicle until maximum movement up and down is
reached. Then let go of bumper and observe if the up and
down motion stops very quickly. If up and down motion
continues longer at one corner when compared to opposite
corner (example, both front shocks), the one having the
longer up and down motion may be suspect.
compare front to rear. If complaint is noise, this test should
help to locate the suspected area.
Inspecting Shock Mountings
If noisy and/or loose shock mountings are suspected,
place vehicle on hoist that supports wheels and check all
mountings for the following conditions:
(1) Worn or defective grommets
(2) Loose mounting nuts
(3) Possible interference condition
(4) Bump stops missing
If no apparent defects are noted in this step but noise
condition still exists when vehicle is bounced up and down,
proceed.
Inspecting Shocks for Leaks and
M anually Operating Shocks
This procedure is sub-divided into two general areas,
(1) Inspecting Shocks for Loss of Hydraulic Fluid and (2)
Manually Operating Shock. It should aid the technician to
localize defective shocks caused by internal noise in the
shock, weak, leaking, etc.
1. Inspecting Shocks for Possible Loss of
Hydraulic Fluid .
(a) Disconnect each shock lower mounting as required
and pull down on the shock until it is fully extended.
(b) Inspect shocks for leaks in seal cover area. Shock
fluid is a very thin hydraulic fluid and has a characteristic
odor and dark brown tint (Figure 3C-8).
Certain precautions
inspecting shocks for leaks:
• shocks may have glossy paint on them. Do not
confuse this paint with a leak condition.
• a slight trace of shock fluid around the seal cover area
is cause for replacement. The shock seal is engineered
not
Do Not
should be observed when
to permit a slight seepage to lubricate the rod. The shock
absorber has reserve fluid to compensate for the slight
seepage.
• shocks are sometimes incorrectly diagnosed as
leakers due to oil spray originating from some other source.
If in doubt, wipe the wet area from and manually operate
shock as described in Step (2). Fluid will reappear if shock
is leaking.
2. M anually Operating Shocks .
It may be necessary with certain types of shock
mountings to fabricate a bracket that can be installed on a
shock to enable a technician to securely grip the shock when
manually operating the shock. See Figure 3C-9 for
suggested methods of providing temporary grip.
This test should help the mechanic to isolate the
following shock defects:
• binding condition internally
• verify leaking shock
• improper or defective valving
(a) If suspected problem is in front shocks, disconnect
both front shock lower mountings and stroke each shock
as follows: Grip the lower end of the shock securely and pull
down (rebound stroke) then push up (compression stroke).
The control arms will limit the movement of the front
shocks during the compression stroke. Compare the
rebound resistance between both front shocks, then
compare the compression resistance. If a noticeable
difference can be felt during either stroke, usually the shock
having the least resistance is at fault.
(b) If shock has an internal noise condition, extend
shock fully, then exert an extra pull. If noisy shock should
be replaced.
Other noise conditions that require shock replacement
are:
• a grunt or squeal after one full stroke in both
directions
• a clicking noise on fast reverse
LIG H T T R U C K S ER V IC E M ANUAL