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0A-81 General Information:
Vibrate Software Description and Operation
The J 38792-VS, Vibrate Software, is a computer
software program which is designed to be used in
support of the Vibration Analysis diagnostic tables, along
with the J 38792-A, Electronic Vibration Analyzer (EVA)
and a scan tool, to help in determining the source of a
vibration concern. The J 38792-VS is designed to
provide quick calculations and produce a chart of the
rotational speeds and frequency ranges for specific
vehicle systems and components, based upon vehicle
data parameters inputted by the user.
The J 38792-VS uses the vehicle data parameters, such
as axle ratio, number of engine cylinders, etc. to create
the base chart, depicting the relationships of the various
vehicle systems and/or components. The chart view can
be modified to show data related to vehicle speed only,
engine speed only, or both vehicle speed and engine
speed. The user can then plot the dominant frequency
reading obtained on the J 38792-A which correlates with
the vibration concern, and the engine RPM obtained on
a scan tool which correlates with the concern. Once
these pieces of data are correctly plotted, the chart will
point to the source of the vibration concern, which
should confirm the results obtained through the following
the Vibration Analysis diagnostic tables.
Reed Tachometer Description
The reed tachometer consists of 2 rows of reeds
arranged side-by-side. Each reed is tuned to vibrate or
resonate when it is excited by a specific frequency. The
reeds are arranged by their specific resonant frequency,
increasing from left to right, ranging from 10-80 Hz. This
arrangement allows for a visual display of the most
dominate frequencies which fall within this range.
The reed tachometer can be a helpful diagnostic tool,
however it is extremely sensitive to external inputs that
are not related to the vibration concern, such as rough
road surfaces, etc., and it is difficult to master its use.
Due to these conditions, the reed tachometer has limited
diagnostic capability.
Due to the limited diagnostic capability, limited
availability and increasing costs of the reed tachometer,
it is NOT recommended as the primary tool to use in
diagnosing a vibration concern.
When diagnosing a vibration concern, use the J 38792-
A, electronic vibration analyzer (EVA). The J 38792-A
has been designed to overcome the shortcomings to the
reed tachometer. Refer to "Electronic Vibration Analyzer
(EVA) Description and Operation".
Special Tools - Squeaks and Rattles
Illustration
Special Tools and Equipment - Vibration
Diagnosis and Correction
Illustration
Tool Number/ Description
J 39570
Chassis Ear
J 41416
Ultrasonic Leak Detector
Tool Number/Description
J 7872
Magnetic Base Dial
Indicator Set
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Troubleshooting
