GMC chervolet camaro 1999 Service Manual page 49

o-46 Vibration Diagnosis and Correction
Diagnostic Information and Procedures
Systematic Approach
During the last 10-15 years, vehicle design and
engineering have dramatically changed due to the
following factors:
• Increased fuel costs
• Decreased fuel supplies
• Corporate Average Fuel Economy requirements
• Clean air legislation
• Foreign competition
• Ability to withstand collision
• Rising customer expectations
Vehicle designs have evolved from full-frame
construction to lighter unibody designs. These designs
transfer noise and vibration much more readily.
General Motors has greatly reduced the use of heavier
and smoother running VB engines, replacing these
engines with lighter, more fuel-efficient 4-cylinder and
6-cylinder engines. During this same time period,
the following options have become increasingly
popular:
• Air conditioning
• Power steering
• All-wheel drive
Such options increase engine load and can also
generate unwanted noise and vibration.
Customer perception of quality can be directly linked
to the presence or absence of unwanted noise
and vibration. The technician's ability to quickly
diagnose and repair a noise or vibration concern
directly affects that customer's loyalty to the
dealership. The technician who is capable of satisfying
this need will be highly regarded and in great
demand.
The intentions of this section of the service manual
are to provide systematic approaches to vehicle
vibration diagnosis and correction. By using the
Strategy Based Diagnosis and the troubleshooting
philosophies covered in this section, the technician will
be able to provide effective and timely repairs.
Diagnostic Information and Procedures
This section describes the techniques and procedures
for correcting the following types of vibrations:
• Tire and wheel shake
• Steering/suspension shimmy and shake
• Launch shudder
• Exhaust moan
• Engine firing frequency
Identifying the Complaint
The first step in diagnosing a vibration complaint is to
identify the exact vibration that concerns the
customer.
Sometimes the vibration can be duplicated at a given
speed. Other vibrations may not be as evident and
may require questioning the customer carefully.
Perform a road test with the customer in the vehicle in
order to determine the specific vibration complaint.
General Information
Ask the following questions when attempting to
identify a vibration complaint:
• At what speed is the vibration the worst?
• Can the customer feel the vibration? If so, where?
• Can the customer hear the vibration?
• Does the engine or the vehicle load affect the
vibration?
• Does the vibration occur in more than one
gear range?
• When did the vibration first appear?
The answers to these questions will help in duplicating
and diagnosing the vibration.
If you suspect that the vibration is normal, compare
the vibration with a vehicle that is equipped in the
same way, including the following factors:
• Body style
• Engine option
• Engine driven accessories
• Transmission type
• Tire size
• Suspension performance type
•.Axle ratio
Important: Do NOT attempt to repair a normal
condition, or the customer will probably be convinced
that the vehicle has a problem. Customer satisfaction
becomes extremely difficult after this point.
If necessary, ride with the customer. Make the
comparison with the customer present and explain the
situation.
Duplicate the Condition
All vehicles produce vibrations. Some vibrations are
normal, while others are not. Some vibrations ca:n
be repaired, some cannot. Duplicate or experience the
customer's complaint. Evaluate the vibration and
the cause of the vibration under changing conditions.
Otherwise, you cannot know for certain that you
are fixing what the customer would like fixed.
The symptoms and characteristics of a noise or
vibration are also important information. Ask yourself
the following questions before you begin:
• What does the vibration feel like?
• Does the vibration make noise? If so, what does
the vibration. sound like?
Different types of noise and vibration have particular
characteristics. These characteristics will help
determine the cause of the condition, and the best
way to correct the condition.
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