steering wheel PONTIAC FIERO 1988 Service User Guide

STEERING, SUSPENSION, TIRES AND WHEELS DIAGNOSIS 3-7
e To determine if turn signal switch is inoperative,
substitute new turn signal switch into circuit and
operate switch by hand.
If the car's lights operate
normally, turn signal switch is inoperative.
Front Or Rear Turn Signal Lights Not Flashing
Inspect
s Burned-out or damaged turn signal bulb
e High resistance conection to ground at bulb
socket
s Loose chassis-to-column connector. Disconnect
column-to-chassis connector and connect new
turn signal switch into system and operate switch
by hand.
A. If turn signal lights are now on and flashing,
turn signal switch is inoperative.
B. If car lights do not operate, refer to Section
8A
for electrical diagnosis.
Turn Indicator Panel Lights
Inspect
Burned out bulbs or opens, grounds in the wiring
harness from the front turn signal bulb socket to the
indicator lights. Refer to Section
8A for electrical
diagnosis.
Stop Light Mot On When Turn Indicated
Inspect
s Loose column-to-chassis connection
e Disconnect the column-to-chassis connector and
connect the new turn signal switch into the
system and operate the switch by hand.
A. If the brake lights work when the switch is
in the turn position, the turn signal switch
is inoperative.
B. If the brake lights do not work, refer to Section
8A for electrical diagnosis.
Turn Signal Lights Flash Very Slowly
e Loose chassis-to-column connection
a Disconnect the column-to-chassis connector and
connect a new turn signal switch into the system
and operate the switch by hand.
A. If the lights flash at a normal rate, the turn
signal switch is inoperative.
B. If the Lights still flash very slowly, refer to
Section
8A for electrical diagnosis.
Hazard Signal Lights Will Not Flash - Turn
Signal Functions Normally
~"SPBC~
a Blown fuse
Inoperative hazard warning flasher
e Loose chassis-to-column connection
s Disconnect the column-to-chassis connector and
connect a new turn signal switch into the system,
then press in the hazard warning button and
watch the hazard warning lights.
A. If the lights now work normally, the turn
signal switch is inoperative.
B. If the lights do not flash, check the wiring
harness. Refer to Section
8A for electrical
diagnosis.
IGNITION SWITCH
Electrical System Will Not Function
Damaged ign~rion switch
e Ignition switch not adjusted properly
e Loose connector at the ignition switch
Switch Will Not Turn
Inspect
Damaged ignition switch
Switch Cannot Be Set Correctly
Inspect
Switch actuator rod deformed
e Sector to rack engaged in wrong tooth
KEY REMINDER
Figs. 1 through 11 ,
Weminder Continues To Operate With Key Out,
But Stops When Driver's Door Is Closed
e Chips, foreign material in lock cylinder bore
Sticky lock cylinder actuator tip
Damaged or broken reminder switch
Reminder Does Not Sound With Key Fully
Inserted In Lock Cylinder And The Driver's Door
Open
Inspect
1. Power not available to reminder. Refer to Sec-
tion
8A for electrical diagnosis.
2. Open in chassis wiring. Check by separating
chassis-to-column connector. Connect terminals
"E" and "F" female contacts on the chassis
connector (a bent paper clip will work). If the
reminder sounds, repair chassis wiring. If the
reminder does not sound, go to Step
A.
A. Connect a continuity meter (light) to the
male
"E" and "F" column connector
contacts. Push the key all the way into the
lock cylinder. If the light is on when the key

3-8 STEERING. SUSPENSION. TIRES AND WHEELS DIAGNOSIS
is in, and off when the key is out, the
function is normal. If the light is not on, the
fault is in the column. Go to Step B.
Fig. 1 Checking Reminder at Chassis Connector
Fig.
2 Checking Reminder at Column Connector
B. Disassemble the upper end of the column
until the turn
signal switch mounting
screws have been
removed. Lift the turn
signal switch and check the probes of the
reminder switch to ensure good contact
with the pads on the signal switch. Bend the
probes, if needed, then replace the turn
signal switch and tighten the three screws.
Check the function as in Step
A.
3. Short or fault in the turn signal switch wiring.
Connect male
"E" and "F" contacts of column
connector with jumper. Check key reminder
switch pads on turn signal switch with continuity
meter. If there is continuity, the function is
normal. If not, replace the turn signal switch. the
key is in the lock cylinder, and off when the
key is out, the function is normal. Retrace the
diagnostic steps starting at Step
A. If the light is
not on, the fault is in the lock cylinder or
reminder switch.
Chips, burrs, or foreign material in the lock
cylinder preventing actuator tip function.
Remove chips, burrs, etc. Reassemble and
recheck (Step 4). The key must be removed, or
the cylinder must be in the "Run" position,
before the lock cylinder can be removed.
Fig. 3 Checking Reminder Switch Pads
6. Damaged lock cylinder. With the lock cylinder
removed, push the key all the way in, then
remove it. The lock cylinder actuator tip should
extend and retract smoothly. Total extension of
tip should be
1.27 mm (.05OU). If not, replace the
lock cylinder. Remove and clean as required.
Reassemble
and recheck per Step 4.
Fig. 4 Checking Reminder Switch
4.. If the problem has not been found, connect a 7. switch appears good but will not operate, continuity meter (light) to the reminder switch
Connect continuity meter leads to the reminder
probes on the switch. Fully insert and remove the
switch probes on the switch. Press on the actuator
key from the lock cylinder. If the light is on when

3-10 STEERING, SUSPENSION, TIRES AND WHEELS DIAGNOSIS
Reminder Keeps Operating With Key In Lock
Cylinder, Driver's Door Open Or Closed; Ceases
When Key Is Removed
Inspect
s Door jamb switch on driver's side misadjusted or
inoperative.
e Wire from signal switch to door jamb switch
shorted.
A. This condition indicates the lock cylinder or
the reminder switch is at fault. To verify,
check for continuity at the
"E" and "F"
male column connector contacts, with the
key removed from the lock cylinder. If
continuity exists, the fault is in the column.
B. Insert the key into the lock, then turn the
lock toward the "Start" position. If the
reminder stops when the key is in the
"Run" position or when it is turned past
"Run" toward "Start," the problem is a
sticky lock cylinder actuator.
COLUMN-MOUNTED DIMMER SWITCH
No "Low" or "High" Beam
Inspect
e Loose connector at dimmer switch
e Improper adjustment
e Internally damaged or worn switch. Check the
continuity on the switch at the It. green and at the
tan switch terminals by pushing in the plunger all
the way.
A click should be heard. If there is no
continuity, replace the dimmer switch. If there is
continuity, refer
to'section 8A for electricaldiag-
nosis.
PIVOT AND SWITCH ASSEMBLY
Switch Inoperative: No "Low," "High" and/or
"Wash"
e Loose body-to-switch connector
a Broken or damaged switch
Internally damaged or worn switch. Connect a
new switch without removing the old one. If the
system functions, replace the switch. If the
system doesn't function, refer to Section
8A for
electrical diagnosis.
STEERING GEAR AND PUMP LEAKS
General Procedure
Inspect
s Overfilled reservoir
s Fluid aeration and overflow
e , Hose connections
Verify exact point of leakage Example:
Torsion bar, stub shaft and
adjuster seals are close together; the exact
spot where the system is leaking may not be
clear.
Example: The point from which the fluid is
dripping is not necessarily the point where
the system is leaking; fluid overflowing from
the reservoir, for instance.
e When service is required:
A. Clean leakage area upon disassembly.
B. Replace leaking seal.
C. Check component sealing surfaces for
damage.
D. Reset bolt torque to specifications, where
required.
Some complaints about the power steering system
may be reported as:
A. Fluid leakage on garage floor
B. Fluid leaks visible on steering gear or pump
C. Growling noise, especially when parking or
when engine is cold
D. Loss of power steering when parking
E. Heavy steering effort
When troubleshooting these kinds of complaints,
check for an external leak in the power steering system.
For further diagnosis of leaks, refer to External
Leakage Check in this section.
External Leakage Check
Fig. 12
The purpose of this procedure is to pinpoint the
location of the leak.
In some cases, the leak can easily be located. But,
seepage-type leaks may be more difficult to isolate. To
locate seepage leaks, use the following method.
1. With the engine off, wipe dry the complete power
steering system.
2. Check the fluid level in the pump's reservoir. Add
fluid if necessary.
3. Start the engine, then turn the steering wheel
from stop to stop several times. Do not hold it at
a stop for any length of time, as this can damage
the power steering pump. It is easier if someone
else operates the steering wheel while you search
for the seepage.
4. Find the exact area of the leak and repair leak.
SEAL REPLACEMENT
RECOMMENDATIONS
Lip seals, which seal rotating shafts, require
special treatment. This type of seal is used on the
steering gear and on the drive shaft of the pump. When
there is a leak in one of these areas, always replace the
seal(s), after inspecting and thoroughly cleaning the
sealing surfaces. Replace the shaft only if very severe
pitting is found. If the corrosion in the lip seal contact
zone is slight, clean the surface of the shaft with crocus
cloth. Replace the shaft only if the leakage cannot be
stopped by first smoothing with crocus cloth.

3-1 2 STEERING, SUSPENSION, TIRES AND WHEELS DIAGNOSIS
POWER STEERlNG SYSTEM "TEST
PROCEDURE
Fig. 13 1. J-5176-D 2. LlNE TO STEERING GEAR
1. Disconnect pressure hose at pump. Use a small 3. LINE TO POWER STEERING PUMP
container to catch any fluid which might leak.
2. Connect a spare pressure hose to pump.
3. Connect pressure gage
J 5176-D
to both hoses.
e The power steering system may be tested
using
J 5 176-D as described here. It can also
be tested with available tool
J 25323 Power
Steering Analyzer, which will measure flow
rate as well as pressure.
4. Open valve on gage.
5. Start the engine. Allow the system to reach
operating temperature, then check the fluid level
and add fluid if required.
6. When the engine is at normal operating
temperature, the pressure reading on the gage
(valve open) should be in the 552-862
kPa (80-125
psi) range. If the pressure is more than 1 380
kPa
(200 psi), check the hoses for restrictions and the
poppet valve on the steering gear for proper
assembly.
7. Fully close the valve 3 times. (Do not leave the
valve fully closed for more than 5 seconds, as the
pump could be damaged.) Record the pressure
reading each time the valve is closed. Each
reading should show at least 6 895
kPa (1,000
psi), or at least 8 619 kPa (1,250 psi) on the TC
series pumps. The three readings should be within
345
kPa (50 psi) of each other.
A. If the pressure readings are high enough,
and are within 345
kPa (50 psi) of each
other, the pump is functioning properly.
B. If the pressure readings are high enough,
but are not within 345
kPa (50 psi) of each
other, the flow control valve in the pump is
sticking. Remove the valve; clean it and
remove any burrs using crocus cloth or fine
hone. If the system contains some dirt, flush
it. If it is exceptionally dirty, both the pump
and the steering gear must be completely
disassembled, cleaned and reassembled.
C. If the pressure readings are less than
6 895
kPa (1,000 psi), or are less than 8 619 kPa
(1,250 psi) on the TC series pumps, replace
the flow control valve and recheck. If the
pressures are still low, replace the rotor and
vanes.
8. If the pump checks to specification, leave the
valve open and turn (or have turned) the steering
wheel to both stops. Record the highest pressures
and compare with the highest pump pressure
recorded. If the pressure at both stops is not the
same as the maximum pressure, the steering gear
is leaking internally and must be disassembled
and repaired.
9. Turn off the engine, then remove the testing gage
and the spare hose. Reconnect the pressure hose,
check the fluid level or make needed repairs.
Fig. 13 Power Steering Pressure Gage
STRUT DAMPENER AND SHOCK
ABSORBER DIAGNOSIS
The strut dampener is basically a shock absorber.
Strut dampeners are easier to extend and retract by
hand than are shock absorbers.
The following procedure includes both on-car
and bench checks to be done when evaluating the
performance of strut dampeners and shock absorbers.
ON-CAR CHECKS
Weak
For struts, follow Steps 1 through 4.
1. Check
and adjust tire pressures to the pressures
shown on the Tire Placard.
2. Note the load conditions under which the car is
normally driven.
3. If practical, ride with the owner to be sure you
understand the complaint before proceeding to
next step.
4. Test each strut
dampener/shock in turn by
quickly pushing down, then lifting up, the corner
of the bumper nearest the strut
dampener/shock
being checked. Use the same amount of effort on
each test and note the resistance on compression
and rebound. Compare this with a similar car
having acceptable ride quality. Both strut
dampeners/shocks should provide the same
feeling of resistance.
If there is much difference between the right and
left rear shocks, go to the next step.
5. Support the rear axle at least enough to unload
the shock mounts.
6. Disconnect the lower shock mountings. Stroke
the shocks at various rates of speed, through
maximum travel in both directions. Compare the
two sides for rebound and compression
resistance. Rebound resistance is normally
stronger than compression (about 2 to 1). The
right and left shocks must feel comparable.
Differences between front and rear are normal. If

STEERING, SUSPENSION, TIRES AND WHEELS DIAGNOSIS 3.13
in doubt about the condition, compare with a
shock known to be good.
Noisy
For struts, follow Steps 1 through 3.
1. Check all mountings for proper torque. A loose
mounting will cause a noise.
2. If all mountings are intact, bounce the car as in
Step
4 (weak) to isolate the suspected unit.
3. If practical, ride with the owner to be sure you
understand the complaint, before proceeding to
next step.
4. If one of the rear shocks is noisy, the rear axle
should be supported at least enough to unload the
shock mounts. Disconnect the lower mounting of
the suspected shock. Quickly push the shock all
the way in, then all the way out.
A hissing noise
is normal.
5. Other objectionable noises may be detected by
stroking. Any sound other
than hissing is
abnormal; replace the shock.
Leaks
1. Fully extend the strut/shocks (wheels
unsupported) to expose the seal cover area for
inspection.
2. Look for
signs of leaks in the seal cover area.
3. A slight trace of fluid is NOT cause for
replacement; the seal permits some seepage to
lubricate the piston rod. There is a built in fluid
reserve to allow for seepage.
4. A leaking strut dampener/shock can easily be
found because there will be fluid around the seal
cover and an excessive amount of fluid on the
strut
dampener/shock. A leaking strut
dampener/shock must be replaced.
BENCH CHECKS
Strut Dampeners and Regular Shock Absorbers
(Standard and Firm Ride)
Regular strut dampenerdrear shocks use a
gas-filled cell in the fluid reservoir. Aeration or
foaming of the fluid is eliminated, as the gas and the
fluid cannot mix.
Proceed with the actual bench check as follows:
1. Clamp the strut dampener/shock UPSIDE
DOWN in the vise. Do not clamp on the reservoir
tube or the mounting threads. If a lag is noticed
when it is stroked, it means the gas-filled cell has
ruptured and replacement is necessary.
2. Pump strut dampener/shock by hand at various
rates of speed and note the resistance.
3. Rebound resistance normally is stronger than
compression resistance by about 2 to 1. However,
the resistance should be smooth and constant for
each stroking rate.
4. Compare with a strut dampener/ shock known to
be good.
5. It is normal to hear a hissing noise. The following
symptoms are abnormal and are reason for
replacement. A.
A skip or lag at reversal near mid-stroke.
B. A seize (except at either extreme end of
travel).
C. A noise (such as a grunt or squeal) after
completing one full stroke in both
directions.
D. A clicking noise at fast reversal.
E. Fluid leakage.
TIRE DIAGNOSIS
Irregular and Premature Wear
Figs. 14 and 15
Irregular and premature tire wear has many
causes. Some of them are: incorrect inflation pressures,
lack of regular rotation, driving habits, or improper
wheel alignment. If wheel alignment is reset due to a
tire wear condition, always reset toe as close to zero
degrees as the specification allows.
1. WEAR INDICATORS I
Fig. 14 Tire Wear Indicator
If the following conditions are noted, rotate the
tires:
@ Front tire wear is different from rear.
Uneven wear exists across the tread of any tire.
e Left and right front tire wear is unequal.
Left and right rear tire wear is unequal.
Check wheel alignment if the following
conditions are noted:
e Left and right front tire wear is unequal.
Wear is uneven across the tread of any front tire.
e Front tire treads have a scuffed appearance with
"feather" edges on one side of the tread ribs or
blocks.
Wear Indicators
Fig. 16
The original equipment tires have built-in tread
wear indicators to show when the tires should be
replaced. These indicators will appear as 12.7 mm
(1/2") wide bands when the tire tread depth becomes
1.6 mm (2/32"). When the indicators appear in 2 or
more grooves at
3 locations, replace the tire.

3-14 STEERING, SUSPENSION, TIRES AND WHEELS DIAGNOSIS
@ HARD CORNERING O UNDER INFLATION LACK OF ROTATION
@ HEAVY ACCELERATION ON DRIVE AXLE EXCESSIVE TOE ON DRIVE AXLE EXCESSIVE TOE ON NON-DRIVE AXLE @ LACK OF ROTATION O LACK. OF ROTAT ION
Fig. 15 Tire Wear Diagnosis
Radial Tire Waddle
Fig. 17
Waddle is side-to-side movement at the front
and/or rear of the car. It can be caused by the steel belt
not being straight within the tire, or by excessive lateral
runout of the tire or wheel. It ig most noticeable at low
speed, about 8 to 48
km/h (5 to 30 mph). It may also
appear as a ride roughness at 80 to 113
km/h (50 to 70
mph). The car can be road tested to see which end of the
car has the faulty tire. If the tire causing the waddle is
on the rear, the rear end of the car will "waddle." From
the driver's seat, it feels as if someone is pushing on the
side of the car.
If the faulty tire is on the front, the waddle is
more easily seen. The front sheet metal appears to be
moving back and forth. It feels as if the driver's seat is
the pivot point in the car.
Another more time-consuming method of
determining the faulty tire is substituting tire and
wheel assemblies that are known to be good. Follow
these steps:
1. Drive the car to determine if the waddle is coming
from the front or rear.
2. Install tire and wheel assemblies known to be
good (from a similar car) in place of those on the
end of the car which is waddling. If the waddle
cannot be isolated to front or rear, start with the
rear tires.
3. Road test again. If improvement is noted, install
the original tire and wheel assemblies one at a
time until the faulty tire is found. If no
improvement is noted, install tires known to be
good in place of all four. Then, install the
originals one at a time until the faulty tire is
found.
Radial Tire Lead/Pull
Fig. 18
"Lead/Pull" is the deviation of the car from a
straight path, on a level road with no pressure
on the
steering wheel.
L Fig. 16 Tire Waddle
Lead is usually caused by:
1. Tire construction.
2. Uneven brake adjustment.
3. Wheel alignment.
The way in which a tire is built can produce lead
in a car. An example of this is placement of the belt.
Off-center belts on radial tires can cause the tire to
develop a side force while rolling straight down the
road. The tire will tend to roll like a cone.
The Radial Tire
Lead/Pull Correction Chart
should be used to make sure that front wheel alignment
is not mistaken for tire lead.
Rear tires will not cause lead.
VIBRATION DIAGNOSIS
See Figs. 19 through 21 for vibration diagnosis.
TAPERED ROLLER BEARING
DlAGNOSlS
See Figs. 22 and 23 for Tapered Roller Bearing
Diagnosis.
See Fig. 24 for Trim Height Diagnosis.

STEERING, SUSPENSION, TIRES AND WHEELS DIAGNOSIS 3-15
REAR-WHEEL DRIVE
RADIAL TIRE LEADIPULL CORRECTION CHART
t rear tlre
rsernblies with right
I I Sar left casttr at top spec, Set right casber at top spec, right caster 1 less. set left caster 1 la.
DO NOT exceed 2' cross caster.
Fig.
17 Radial Tire Lead/Pull Diagnosis - Rear-Wheel Drive

3-16 STEERING, SUSPENSION, TIRES AND WHEELS DIAGNOSIS
SUSPENSION MOVEMENT
(Loaded Runout)
. LC----- '-- / 0 B 0 -=---I --..,-----=-
CAUSED BY
TIRE OUT
0 F
ROUND
TIRE
STIFFNESS
VARIATION RIM
BENT 0 R OUT OF ROUND
G33830-3-AN
Fig. 18 Causes of Vibrations

STEERING, SUSPENSION, TIRES AND WHEELS DIAGNOSIS 3-17
Fig. 19 Vibration Complaint Chart (1 of 2)

3-18 STEERING, SUSPENSION, TIRES AND WHEELS DIAGNOSIS
VIBRATION COMPLANT TIRE-WHEEL-HUB-AXLE RELATED
Vibrations that are tire or wheel induced can be caused
by two factors: imbalance or
runout. Low-speed vibrations, those less than 40 mph, are
usually runout related. Highway speed vibrations, those
above 40 mph, can be caused by either imbalance or runout. Prior to performing any work, always road test the car
and perform a careful visual inspection for:
- Obvious tire and wheel runout. - Obvious drive 'axle or propeller shaft runout. - Proper inflation pressure. - Wrong trim height. - Bent wheels. - Debris build-up on the tire or wheel. - Loose or missing wheel weights or wheel nuts. - Irregular or excessive tire wear. - Proper tire bead seating on rim. - Damaged tires, such as tread distortions,
separations, or bulges from impact damage. Slight sidewall indentations are normal and will not affect
ride quality.
Balance is the easiest procedure to perform and should,
therefore, be done fist if the vibration occurs at highway
speeds.
An off-car two-plane dynamic balance should first
be performed. This will correct any imbalance in the tire and
wheel assembly.
An oncar fiish balance may also be required. This will correct any brake drum, rotor, or wheel cover imbalance.
Follow the balancing procedures outlined in Section 3E. If balance does not correct the highway speed vibration,
or if the vibration is at low speeds, runout is the probable
cause. Runout can be caused by the tire, wheel, or the way
the wheel attaches to the car. The following procedure
should be used
: A. If runout is suspected, the free runout of the tire
and wheel assembly should first be measured on the car. A
dial indicator with a roller wheel is preferable, but a dial
indicator with button end may be used. Lateral
runout (side
to side) should be measured on the tire's sidewall as close to
the tread shoulder as possible. Radial
runout (up and down)
should be measured on the center tread rib. Some tread
designs may require tightly wrapping a piece of tape around
the center tread circumference for better dial indicator
contact. For measuring wheel
runout follow the "Measuring
Wheel Runout" procedure in Section 3E. Whether measuring
radial or lateral runout, disregard any instantaneous indicator
needle jumps due to sidewall depressions, tread blocks, etc.
Record the total indicator reading, and the location of the
high point of
runout. The,,total tire and wheel oncar runout should be less than ,060 , if either measurement exceeds ,060"~ proceed to Step B.
B. If
the oncy radial or lateral runout measured in
Step A exceeds .060 , mount the tire and wheel assembly on
a dynamic balance machine and again measure the amount of runout. Locate on the machine by the wheel's inside center
pilot hole. Using the same procedure as in Step A, record the
amount of tire and wheel
runout and its high point Location.
Next, measure wheel runout, see Section 3E. If the wheel
exceeds specifications replace the ~heel.,~If the tire and wheel
radial or lateral runout exceeds .050 at the tire tread,
proceed to Step C.
C. If the off-car tire and wheel radial or lateral runout measured in Step 18 exceeds .050", match mount the high radial runout point of tire to low radial runout point of
wheel. Weinflate, mount on the dynamic balance machine,
and again measure and record the radial and lateral runout and its location, as done in Step B. In many cases, match
mounting the tire on the wheel will bring the assembly's
runout into the acceptable range of less than .050". D. If the runout of the tire and wheel assembly is
within limits when measured off the car, yet exceeds the
limits when measured on the car, the attachment of the tire
and wheel assembly to the hub is the probable cause. Rotate
the assembly two wheel studs and recheck the
runout. Several positions may have to be tried to find the best
location.
E. If the assembly runout cannot be reduced to an
acceptable level, remove the tire and wheel assembly and
measure wheel stud
runout with a dial indicator. Zero
the dial indicator button on one stud. Lift button gently
off stud and rotate flange to position next stud against
dial indicator button. Record the
runout on all studs. Dial indicator should read zero when repositioned on first stud
that was checked. If runout exceeds .030", the hub or axle
shaft should be replaced.
Whenever a tire is rotated on the wheel, or a tire or
wheel is replaced, the assembly must be rebalanced.
In addition to balance and tire and wheel free
runout, tire stiffness variation (loaded radial runout) can also cause
a vibration. However, this is impossible to measure without
a TPD (Tire Problem Detector) or a loaded radial
runout buffer.
The TPD is a roller drum that slowly rotates the tire
while under load and mounted on the car. Tire stiffness
variation causes wheel spindle movement which can be
measured.
The loaded radial
runout buffer is a more automated
machine that slowly rotates the tire and wheel off the car
under load with a roller drum and measures the tire's
stiffness variation. It will then "match" the tire to the wheel
by buffing off small amounts of rubber from the outer tread
rows at the stiff spot. This procedure is usually effective,
especially when used
as a measuring device and for fine
buffing only.
The
TPD and loaded radial runout buffer are two
methods that will measure or correct tire stiffness variation,
tire
runout, and wheel runout at the same time. However,
because such equipment is not always available, and both
have their disadvantages, the more basic procedure of
measuring free
runout with a dial indicator, as previously
detailed, is usually more practical. The free runout of the
tire will usually correspond with the tire's stiff spot.
The substitution method of vibration diagnosis can also
be used. Install
a known good set of tire and wheel
assemblies. If these correct the vibration, the original
assemblies should be reinstalled one at
a time until the
vibration returns. This will point out the tire with excess
stiffness variation.
Tire stiffness variation will be higher or lower depending
on the direction of tire rotation.
Fig. 20 Vibration Complaint Chart (2 of 2)