Strobe Balance Testing With the Elect Vibration Analyzer (Eva)

Ensure that the runout of the various driveline components are within specifications. If the runouts are within specifications, strobe balance the driveline. The EVA is able to simplify the balancing process, using the following procedure:
1. Use the EVA in order to determine which end of the propeller shaft has the most vibration.




2. Mark the end of the propeller shaft that has the most vibration at 4 points, 90 ° apart. Number the marks 1-4.
3. Mount the EVA sensor onto the bottom of the following components:
- The differential housing
- The center bearing support (for those 2-piece propeller shafts which use a center bearing support)
- The transmission tailshaft assembly
4. Position the sensor as close to the propeller shaft as possible. Verify that the UP side of the sensor faces up and verify that the sensor is horizontal.
5. Start the engine.
6. Turn OFF all engine accessories.
7. Place the transmission in gear.
8. Run the vehicle at the speed which causes the most vibration in the propeller shaft.
9. Hook the timing light clip to the trigger wire.
10. Plug the vibration sensor into Input A of the EVA. Input Bis not applicable for this test.
11. Verify that the predominant frequency on the EVA display matches the frequency of the original vibration. Use the strobe light only if the rotation speed of the propeller shaft is the predominant frequency.
12. The EVA displays a series of questions in order to select the correct filter. Press YES in order to select the desired filter. Ensure that the frequency is in the middle of the filter range. Use the full range only as a last resort.
13. The display shows the test frequency, the amplitude and the filter range. The driveline is balanced when the amplitude is near 2. In some cases, a slightly higher amplitude will provide adequate balance.
14. Point the timing light at the propeller shaft. The strobe effect will appear to freeze the propeller shaft. Remember which of the numbered marks is at the bottom of the propeller shaft, or the 6 o'clock position. This position is the light spot.
15. Turn the engine OFF.
16. Install a weight directly on the light spot.
17. Start the engine.
18. Run the vehicle at peak vibration speed.
19. Strobe the propeller shaft again.
- The propeller shaft is balanced if the strobe image is erratic and the amplitude is near 2.
- The propeller shaft is not balanced if one of the following conditions exist:
- The weight and the original light spot are at the 6 o'clock position.
The above condition means that there is not enough weight on the propeller shaft. In order to correct the balance, add a second weight next to the first weight. Inspect the balance again using the strobe light.




- If the weights are now 90 - 180 ° off (between the 9 o'clock and the 3 o'clock positions) too much weight exists. In order to correct the balance, split the 2 weights equally on either side of the original light spot in order to produce a total weight between 1 - 2 weights (between 0 - 120 ° apart). Inspect the balance again using the strobe light. Adjust the weights as necessary.
- The weight and original light spot are 90 - 180 ° off (between the 9 o'clock and the 3 o'clock positions).
The above condition means that I weight is too much. In order to correct the balance, split the 2 weights equally on either side of the original light spot in order to produce a total weight less than 1 (120 - 180 ° apart). Inspect the balance again using the strobe light. Adjust the weights as necessary.
- The weight and the original light spot are within 180 ° of the 6 o'clock position.
Move the weight towards the 6 o'clock position. Inspect the balance again using the strobe light. Adjust the weight as necessary. Refer to the previous 2 conditions.
If the shaft will not balance using 2 weights, place a third weight on the light spot. Split the first 2 weights in order to produce a total weight between 2 and 3 weights.
If 3 weights fail to balance the driveline, replace the propeller shaft.
When the propeller shaft balances, road test the vehicle in order to verify that the vibration is eliminated