Important: If you have not reviewed the Diagnostic Starting Point - Vibration Diagnosis
and completed the Vibration Analysis Tables as indicated, refer to
Diagnostic Starting Point - Vibration Diagnosis and Correction
BEFORE proceeding.
The diagnostic information contained in this Diagnostic Aids section will help
you determine the correct course of action to take for the following four main conditions.
Refer to the appropriate condition following this list:
| • | Vibration NOT Duplicated or Intermittent Duplication |
| • | Vibration Duplicated - Difficult to Identify or Isolate Component |
| • | Vibration Duplicated - Difficult to Balance or Isolate Component |
| • | Vibration Duplicated - Appears to be a Design Inherent Condition |
Vibration NOT Duplicated or Intermittent Duplication
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
Most attempts to duplicate a vibration concern are made after the vehicle has
been driven to the dealership and perhaps even sat inside the building for a time.
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. The selection of roadways used to perform the vibration duplication
procedures is likely to be in the near vicinity of the dealership. The vehicle is
most likely empty of any payloads and usually not bearing any kind of trailer.
Caution: Do NOT attempt to duplicate a vibration concern with specific conditions
indicated by the customer which would disobey local laws or ordinances, or
which could cause damage to the vehicle or be dangerous and possibly cause
physical injury or death, such as over-loading a vehicle, or driving at excessive
vehicle speeds.
Important: If the information you gained from the customer indicates that one or more
of the specific conditions listed applies to their concern, attempt to duplicate
the vibration concern again, while carefully recreating the EXACT conditions necessary,
with the exception of excessive speed, over-loading the vehicle or towing a trailer.
You are responsible to make sure that the vehicle operates normally 'as-designed'
and under 'normal operating conditions' ONLY.
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, then 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.
Temperature, Ground-Out, Accessory Load
| | 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 fully warmed-up. 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 to 5 cm (1 to 2 in)
when hot.] |
| • | Engine-Driven Accessory Noises |
| - | An engine accessory drive belt (or belts) could exhibit a whipping condition
if the 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. |
| - | These 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 |
| - | These 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 Pulley(s) |
| - | Bent or mis-aligned pulley(s) in one or more engine-driven accessory systems
could contribute to a noise or vibration condition. |
| - | Fluid Level in Accessory System(s) |
| - | These accessories could exhibit a noise condition due to an abnormal amount
of fluid contained in the system of which the accessory is a part. |
| • | 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 System(s) |
| - | These 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 vehicle may have been empty during attempts to duplicate the vibration
concern, while the customer may actually experience the vibration concern while
the vehicle is carrying a large payload. |
| | The customer may experience the vibration concern only while towing a trailer. |
Roadway Selection
The customer may only experience the vibration on a particular roadway. Perhaps
the roadway is overly crowned or is very bumpy or rough.
Vibration Duplicated - Difficult to Identify or Isolate Component
Aftermarket Add-On Accessories
Aftermarket accessories which have been added to the vehicle can actually transmit
and magnify INHERENT component rotational frequencies, if the accessories were not
installed correctly.
An accessory should be installed in such a way that it is isolated from becoming
a possible transfer path into the rest of the vehicle. For example, if a set of
running boards has been installed improperly and they are sensitive to a particular
frequency of a rotating component, the running boards could begin to respond to
the frequency and actually create a disturbance once the amplitude of the frequency
reaches a high enough point (probably at a higher vehicle speed).
Vibration Duplicated - Difficult to Balance or Isolate Component
If you have duplicated the vibration concern but have had difficulty in balancing
a component or isolating a component, refer to the following information.
Most vibration concerns are corrected or eliminated through correcting excessive
runout of a component, correcting balance of a component or isolating a component
which has come into abnormal contact with another object/component.
Components which can generate a lot of energy and are experiencing excessive
runout, imbalance or ground-out can produce a vibration with a strong enough amplitude
that the vibration can transmit to components which are closely related. This type
of a condition is usually related to and sensitive to torque-load. The most likely
system that could exhibit this type of a condition is the driveline.
Driveline Torque-Load Conditions
An axle differential that has internal problems such as excessive runout of
components, misalignment of components, imbalance, etc., can produce vibration concerns
which may be transmitted into the propeller shafts. This sort of a vibration occurrence
can increase or decrease in severity based primarily upon torque-load, but can also
be affected by cold or hot conditions.
The propeller shaft and other related components may or may not pass inspections
for wear or damage, runout, alignment, etc., depending upon whether there is only
one vibration source or more than one.
Difficult to System Balance the Driveline
If after following the Vibration Analysis - Driveline Table you were
instructed to system balance the driveline and you experienced difficulty in doing
so while CAREFULLY following the procedures indicated (the EVA strobe readings seem
to keep changing), then the axle differential to which the propeller shaft is attached
should be suspected to have internal problems which are being transmitted to the
propeller shaft. Refer to
Noise Diagnosis - Rear Drive Axle
in Rear Drive
Axle.
Vibration Duplicated - Appears to be a Design Inherent Condition
Check Service Bulletins
If BOTH of the following statements are TRUE, then check service bulletins
for the condition identified. If the condition has already been identified and investigated
prior to this vehicle, and has been determined to be something that is not truly
design-inherent or that perhaps is not design-intent, there will likely be adjustments
or corrections identified which will address the condition.
- You CAREFULLY followed the steps indicated through reviewing the Diagnostic
Starting Point - Vibration Diagnosis and completing the Vibration Analysis
Tables identified and you have duplicated the vibration concern.
- You have come to the conclusion through comparison with a very equally-equipped,
same model year and type, KNOWN GOOD vehicle that the customer's concern is a condition
inherent to the design of the vehicle.
