Important: If you have not completed the Vibration Analysis tables as indicated and reviewed Diagnostic Aids, refer to
Vibration Diagnostic Aids BEFORE operation.
If you have not been able to duplicate the vibration concern or 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 duplication attempts, or due to not following the procedures designed for duplication concerns and in the sequence as indicated.
Specific Conditions Can Affect the Vibration Condition
Consider the following conditions which may not have been present while vibration concerns are duplicated. 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 overloading.
Most attempts to duplicate a vibration concern are made after the vehicle has been driven to GM SPO and perhaps even sat inside the building for a time; but the vehicle may be too warm to detect the concern during duplication efforts. Meanwhile, the vehicle
may be too cold to detect the concern, if the vehicle has been placed in the cold for a time and fails to reach the full operation temperature during attempts to duplicate the concern.
Temperatures, 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 been warmed and softened.
Exhaust System Growth
Exhaust systems may exhibit a ground-out condition when cool, while this condition goes away once the system is hot. The opposite may be true, the exhaust system is fine when cool while a ground-out condition occurs once the system reaches the operation
temperature. The Exhaust system can grow by 2½-5 cm (1-2 in) when hot.
Engine-Driven Accessory Noises
| | Engine accessory drive belt 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 a ground-out
condition exhibited on relative components of the system during certain operation of that accessory system. |
| | Accessories could exhibit noise when cool, while the noise goes away once they are fully warmed - up, or the opposite may be true. |
| • | Load on an Accessory Component |
| | Accessories could exhibit noise conditions while under a heavy load - perhaps accompanied with a cool or fully warmed-up condition. |
| • | Bent or damaged pulleys |
| | Bent or mis-aligned pulleys contained in one or more engine-driven accessory system(s) could contribute to noise or vibration condition. |
| • | Fluid Level in Accessory System |
| | Accessories could exhibit noise conditions 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 A/C refrigerant level or an excessive amount of refrigerant oil could produce noises or possibly vibrations in an A/C system. |
| • | Incorrect Fluid Type in Accessory System |
| | Accessories could exhibit noise conditions 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 actually the customer may experience the vibration concern when the vehicle is carrying a large payload.
Trailer Towing
The customer may experience the vibration concern only while towing a trailer.
Roadway Selection
The road used to perform the vibration duplication procedures is likely to be in the near vicinity of the GM SOP, and may not provide the similar road 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.
