Chevrolet Cobalt Service & Repair Manual: Vibration, Diagnosis
| The designs and engineering requirements
of vehicles have undergone drastic changes over the last several years.
Vehicles are stiffer and provide more isolation from road input than they
did previously. The structures of today's stiffer vehicles are less susceptible
to many of the vibrations which could be present in vehicles of earlier
designs, however, vibrations can still be detected in a more modern vehicle
if a transfer path is created between a rotating component and the body
of the vehicle. |
| There are not as many points of
isolation from the road in many vehicles today. If a component produces
a strong enough vibration, it may overcome the existing isolation and the
component needs to be repaired or replaced. |
| Rotating components will cause
vibrations when excessive imbalance or runout is present. |
| A vibrating component operates
at a consistent rate (mph or RPM). Measure the rate of vibration in question.
When the rate/speed is determined, relate the vibration to a component that
operates at an equal rate/speed in order to pinpoint the source. Vibrations
also tend to transmit through the body structure to other components. Therefore,
just because the seat vibrates does not mean the source of vibration is
in the seat. |
Visual
| When diagnosing vibrations it
is imperative to notice when and where the vibrations occur. Test drive
the vehicle with this in mind. You need to determine whether the vibrations
are a tire issue, an engine or drive train problem or exhaust issue. Feel
for the vibrations at an idle state and whether they are felt in the steering
wheel. Put the car in gear and see if the vibrations lessen or increase.
Drive the car at 10 to 20 miles per hour and feel for side to side shifts
and vibrations. Inspect to see if the vibrations get faster as speed increases.
Inspect to see if there are vibrations going over bumps. Drive the car over
45 miles per hour and notice if you feel the vibrations increasing in the
steering wheel. Inspect the appropriate steps that apply to the vibrations
felt in your test drive for the proper order of diagnosis. |
| 1. |
Inspect front tires for a lateral or
side to side vibrations at slow speeds by jacking up each tire individually.
Grasp tire on top and bottom and try to rock tire. If there is play
when moving tire in and out, bearing/hub bearing is bad and needs
to be replaced. |
| 2. |
Inspect for significant damage to tire.
Visually inspect if there are any bulges on inside or outside of
tire. Look for any deformities as you rotate tire, such as uneven
wear or steel protruding out of tread. |
| 3. |
Inspect all tires for cupping of tread.
This is an unevenness of tread that you feel as your hand is run
across tread. Look for flat spots on tires created by a panic stop
where tires were locked up and slid removing rubber on that spot.
This will generate vibrations at all speeds. |
| 4. |
Inspect front tires for balancing if
vibration is only at speeds in excess of 45 miles per hour. |
| 5. |
Inspect engine for vibrations. Test
for broken or worn motor/transmission mounts with aid from an assistant. |
| 6. |
Put transmission in neutral, leave
door open, and rev engine up to about 3000 RPM. If noise and vibration
can be heard in middle of car it is most likely shield on catalytic
converter, which often gets bent and contacts either converter or
body. |
| 7. |
Inspect exhaust by shaking pipe and
see if it contacts body. |
|
Electronic
| An Electronic Vibration Analyzer
(EVA), is a hand-held device, similar to a scan tool, which receives input
from an attached vibration sensor or accelerometer and displays the most
dominate input frequencies on its liquid crystal display. The vibration
concern frequencies are obtained through the use of the electronic vibration
analyzer while following the vibration analysis diagnostic tables. The frequencies
obtained, when applied to the vibration analysis diagnostic tables, are
used as a primary input to help determine the source of the vibration concern. |
| Proper placement of the EVA vibration
sensor (accelerometer) is critical to ensure that proper vibration readings
are obtained by the EVA. The vibration sensor should be placed on the specific
vehicle component identified as being the most respondent to the vibration.
If no component has been identified, install the sensor to the steering
column as a starting point. |
| The vibration sensor of the EVA
is designed to pickup disturbances which primarily occur in the vertical
plane, since most vibrations are felt in that same up and down direction.
The EVA vibration sensor is therefore directional sensitive and must be
attached to vehicle components such that the side of the sensor marked UP
is always facing upright and the sensor body is as close to horizontal as
possible. The sensor must be installed in the exact same position each time
tests are repeated or comparisons are made to other vehicles. |
| The EVA vibration sensor can be
attached to vehicle components in various ways. For non-ferrous surfaces,
such as the shroud of a steering column, the sensor can be attached using
putty, or hook and loop fasteners. For ferrous surfaces, the sensor can
be attached using a magnet supplied with the sensor. |
| 1. |
Attach EVA vibration sensor to area
where vibration occurs. |
| 2. |
Recreate vibration condition. |
| 3. |
Record readings from EVA unit. |
| 4. |
Compare readings to vibration analysis
diagnostic tables. |
| 5. |
If results are inconclusive, reposition
vibration sensor and test again. |
|
Front
Outer
1.
Raise and support vehicle using suitable
lift.
2.
Remove tire and wheel assemblies.
3.
Remo ...
Front
1.
Raise and support vehicle using suitable
lift.
2.
Remove tire and wheel assemblies.
3.
Remove driv ...
Tie Rod, Replace
Wheel Bearing, Replace