Identifying the Concern
The first step in diagnosing the vibration concern is identifying the
EXACT vibration that the customer is complaining about. Most importantly,
road testing will determine whether the vibration is related to the engine
speed (RPM) or the vehicle road speed (km/h, mph). The next step is to pinpoint
the operating conditions that change or eliminate the vibration.
Sometimes the vibration may be easily duplicated at a given speed. Other
vibrations may not be as evident and may require questioning the customer
carefully to be sure that all repair efforts are focused on the same vibration
that is displeasing the customer. It may be helpful or sometimes mandatory
to road test the vehicle WITH the customer, so that the customer may point
out the specific vibration. During this phase of the diagnosis, the following
questions need to be answered:
| • | At what speed is the vibration the worst? |
| • | Can the vibration be felt? If so, where? |
| • | Can the vibration be heard? If so, what does the noise sound like? |
| • | Does the engine or 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 may be necessary in order to diagnose
or duplicate the vibration.
If the vibration that has been duplicated is suspected as being normal
for the specific model, compare the vibration with a vehicle that is equipped
in the same way; including the following:
| • | Engine driven accessories |
| • | Suspension performance type |
If necessary, make the comparison between vehicles with the CUSTOMER
PRESENT and explain the situation. This is EXTREMELY important. Once an attempt
is made to repair what may be a NORMAL condition, the customer will likely
be convinced that a true concern exists with the vehicle and satisfying that
customer becomes much more difficult.
Determining the Component Group
After a vibration has been categorized as being engine-speed or vehicle-speed
related, the vibration can be broken down further to fit into one of the following
three groups of rotating components:
| • | The engine, clutch drive plate and driven plate (M/T), propeller
shaft (within the driveline support assembly) and transmission torque converter
(A/T) |
| • | The transmission output shaft and rear axle differential pinion
(mounted in the rear end of the differential) |
| • | The tires, wheels, wheel hubs/axle flanges, and brake rotors |
These three groups represent the three most-common vehicle areas that
can produce vibration conditions. The components in each group are related
to each other because they are either bolted or splined together. This means
that the components within each group rotate at the exact same speed.
By further testing and measuring, these three categories may be broken
down further still, in order to identify the exact component responsible for
the disturbance. The emphasis is on testing (and more testing) in order to
pinpoint the source and to eliminate unneeded part replacement.
Types of Road Tests
The following are the most often used and informative road test procedures:
| • | Tire and Wheel Inspection |
| • | Neutral Coast-Down Test |
| • | Standing Start Acceleration Test |
Road Testing
Caution: Road test a vehicle under safe conditions and while obeying all traffic laws.
Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere
to these precautions could lead to serious personal injury and vehicle damage.
If these
road tests are performed and interpreted properly, they will help to break
the vehicle down into the previously mentioned categories and component groups
and enable repair efforts to be concentrated on a specific part of the vehicle.
All of the road tests should be performed on smooth, level surfaces.
In order to complete a quick and accurate road test, install both an
engine tachometer (such as a scan tool) and the Smart Electronic Vibration
Analyzer (Smart EVA) in the vehicle prior to the test. Ensure that the Smart
EVA vibration sensor is placed in a location where the customer's concern
can be FELT.
Important: In order to avoid focusing diagnosis and repair efforts in unproductive
areas; proceed through the road testing diagnosis information and perform
ALL of the required tests (as indicated), in addition, perform as many of
the additional inspections and tests as necessary to narrow down the vibration
as much as possible.
After the completion of the necessary road testing diagnosis inspections
and tests, proceed to
Classifying the Vibration
.
Tire and Wheel Inspection
This test should be performed for ALL vibration conditions UNLESS the
disturbance occurs with the vehicle at a standstill.
