Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. 4. Obtaining rotational speed for the components rotating at both tire/wheel speed and driveline speed is critical to systematically eliminating specific vehicle component groups. These component rotational speeds can be generated by using the J 38792-VS, Vibrate Software, or through calculating them manually
2. 8. Important:  Be certain to OBSERVE for disturbances that match the customer's description FIRST, then look at the J 38792-A frequency which corresponds with that disturbance

   Proper location of the J 38792-A, Electronic Vibration Analyzer (EVA) 2, sensor onto the component which is most excited by the vibration disturbance is critical to obtaining an accurate frequency reading.

   This test will duplicate virtually any disturbance which occurs while the vehicle is in motion.

3. 9. Accelerate to a speed high enough above the speed of the disturbance to allow for the time needed to shift into NEUTRAL and for the engine to decrease in RPM to idle speed, before coasting down through the disturbance range
4. 10. This test will either eliminate or confirm the engine as a contributing cause of the customer concern
   Fig 1: Vibration Analysis - Road Testing (1 -4)

   Courtesy of GENERAL MOTORS CORP.
   Fig 2: Vibration Analysis - Road Testing (5 - 7)

   Courtesy of GENERAL MOTORS CORP.
   Fig 3: Vibration Analysis - Road Testing (8 -9)

   Courtesy of GENERAL MOTORS CORP.
   Fig 4: Vibration Analysis - Road Testing (10 - 12)

   Courtesy of GENERAL MOTORS CORP.