Vibration Diagnostic Aids - Vibration Intermittent or Not Duplicated
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 tyres
Tyres which have sat and been cool for a time can develop flat spots.
Irregular Wear on tyre Treads
Tyres 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 tyres 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
Note: 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.
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 an alternator, 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.
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