Important: If you have not completed the Vibration Analysis tables as indicated and reviewed
Vibration Diagnostic Aids, refer to
Vibration Diagnostic Aids
BEFORE proceeding.
If you have not been able to duplicate the vibration concern or have only been
able to duplicate the concern intermittently, review the following information.
Most vibration concerns that cannot be duplicated are due to either specific
conditions that are not present during the duplicating attempts, or due to not following
the procedures designed to duplicate concerns properly and in the sequence indicated.
Specific Conditions Can Affect the Condition
Consider the following conditions which may not have been present while attempts
were made to duplicate the vibration concern. Attempt to obtain more specific information
from the customer as to the EXACT conditions that are present when they experience
the vibration which they are concerned about. Attempt to duplicate the vibration concern
again while recreating the EXACT conditions necessary, except those which pose a safety
concern or are outside the boundaries of normal operating conditions, such as loading
the vehicle beyond its designed weight ratings, etc.
Most attempts to duplicate a vibration concern are made after the vehicle has
been driven to the repair facility and perhaps even sat inside the building for a
time; the vehicle may be too warm to detect the concern during duplication efforts.
The opposite could also occur; perhaps the vehicle has sat out in the cold for a time
and fails to reach full operating temperatures during attempts to duplicate the concern.
Temperature, Ground-Out, Accessory Load
Flat Spots on Tires
Tires which have sat and been cool for a time can develop flat spots.
Irregular Wear on Tire Treads
Tires which have sat and been cool for a time will be stiffer and any irregular
wear conditions will be more noticeable than they will be once the tires have warmed
and softened.
Exhaust System Growth
Exhaust systems may exhibit a ground-out condition when cool which goes away
once the system is hot. The opposite may be true that the exhaust system is fine when
cool but a ground-out condition occurs once the system reaches operating temperatures.
Exhaust systems can grow by 2½-5 cm (1-2 in) when
hot.
Engine-Driven Accessory Noises
Important: When a stethoscope equipped with a probe is used to assist in identifying possible
vibrating components, the results must be compared to the sound quality of the same
accessory, in a equally-equipped, same model year and type, KNOWN GOOD vehicle, and
under the same conditions. Refer to
Vehicle-to-Vehicle Diagnostic Comparison
.
A stethoscope equipped with a probe can be used as an additional means to assist
in identifying accessories which may be causing or contributing to a vibration concern.
| | An engine accessory drive belt, or belts could exhibit a whipping condition
if a belt is deteriorating and deposits are building up on the underside of the belt. |
| • | Loose Mounting Brackets or Component Ground-Out |
| | Engine-driven accessories such as a generator, a power steering pump, or an
air conditioning compressor could exhibit noise conditions due to either loose mounting
brackets or due to related components of the system in a ground-out condition during
certain operation of that accessory system. |
| | Accessories could exhibit noise conditions when cool which go away once they
are fully warmed-up, or the opposite may be true. |
| • | Load on an Accessory Component |
| | Accessories could exhibit a noise condition while under a heavy load -
perhaps when combined with a cool or fully warmed-up condition. |
| • | Bent or Misaligned Pulleys |
| | Bent or mis-aligned pulleys in one or more engine-driven accessory systems could
contribute to a noise or vibration condition. |
| • | Fluid Level in Accessory Systems |
| | Accessories could exhibit a noise condition due to an abnormal amount of fluid
contained in the system of which the accessory is a part. For example: |
| - | An improper power steering fluid level could produce noises in the power
steering system. |
| - | An improper air conditioning refrigerant level or an excessive amount
of refrigerant oil could produce noises or possibly vibrations in the air conditioning
system. |
| • | Incorrect Fluid Type in Accessory Systems |
| | Accessories could exhibit a noise condition due to the incorrect type of fluid
contained in the system of which the accessory is a part. |
Vehicle Payload
The vibration concern may only occur when the vehicle is carrying heavy payloads
or towing a trailer; the vehicle may have been empty during duplication efforts.
Heavy Payload
The vehicle may have been empty during attempts to duplicate the vibration
concern, but the customer may actually experience the vibration concern while the
vehicle is carrying a large payload.
Trailer Towing
The customer may experience the vibration concern only while towing a trailer.
Roadway Selection
The selection of roadways used to perform the vibration duplication procedures
is likely to be in the near vicinity of the repair facility and may not provide a
road surface that is similar enough to the surface on which the customer usually drives
the vehicle.
The customer may only experience the vibration on a particular roadway. Perhaps
the roadway is overly crowned or is very bumpy or rough.
