System Balancing Using an EVA

Before starting, be sure that the runout of the driveline components is within specification. This information can be found in the Workshop Manual or in this Diagnostic Procedure. If components are found to be good, proceed with strobe balancing using the EVA.

1. Number the ends of the driveshaft by the transmission and the axle pinion 1 through 4, putting a number every 90 degrees. Then place an accelerometer at each end of the driveshaft.

2. Mount the accelerometer on the bottom of the rear axle differential or the transmission tailshaft. Be sure to position the sensor as close to the driveshaft as possible, assuring that the UP side of the accelerometer is up and the sensor is horizontal.

3. Have the vehicle positioned on a hoist and set up on jack stands to level the vehicle with the wheels removed.

NOTE
BEFORE STARTING TO STROBE THE VEHICLE, BE SURE ALL LOOSE ARTICLES ARE CLEAR OF MOVING COMPONENTS. NEVER TOUCH MOVING PARTS WITH YOUR HANDS.

4. Turn off all accessories and have an associate start the engine. Place the engine in gear and accelerate the vehicle to speed where the vibration occurs.

5. With an inductive timing light clipped to the trigger wire of the EVA and the accelerometer plugged into Input A, be sure both the EVA and timing light have a 12 volt source.

6. Verify that the predominant frequency displayed on the EVA matches the frequency of the original reading taken with the EVA. Press "STROBE" key on EVA pad. The EVA will display a series of questions in order to select the correct filter. Press YES to select the correct filter. Be sure that the frequency is in the middle of the filter range. Use full range only if these ranges do not give the desired results.

7. The display on the EVA shows the test frequency, the amplitude, and the filter range. The driveline is balanced when the "strobe amp" is between 0-4, or when the flashing strobe becomes erratic or ceases.

8. Point the timing light at the driveshaft. The strobe will appear to freeze the driveshaft. Note at which of the numbered marks it is on or closest to. This is the light spot.

9. Turn off the vehicle. Let all components come to a complete stop.

10. Install weight directly on the spot that was identified by the strobe. This is the light spot on the driveshaft.

11. Start vehicle and run to vibration speed.

12. Strobe the driveshaft again. The driveline is in balance when the EVA level is between 0-4, or when the flashing strobe becomes erratic or ceases.

13. The driveshaft is not balanced if the following conditions exist:

^ If the weight that was placed on the light spot is at the 6 o'clock position, the area is still light. Add another weight next to this area, run the vehicle, and inspect the balance again with the strobe light.

^ If the weights are between the 9 and 3 o'clock position, 90 to 180 degrees off one weight is too much. To correct this condition take the two weights and move them 120 degrees with the light spot in the center. Recheck the balance using the timing light and adjust as necessary, always noting if the vibration has gone.

^ If one weight and the original light spot are between 9 and 3 o'clock, one weight is too much. To correct this condition split two weights equally on either side of the original light spot to make a total weight of less than one. Recheck the balance using the timing light and adjust the position of the weights as needed.

^ If the weight and light spot are 180 degrees of the 6 o'clock position, move the weight toward the 6 o'clock position. Recheck the balance using the timing light and adjust the position of the weight as needed. Refer to previous steps to resolve if further adjustment is needed.

^ If the shaft will not balance using two weights then add a third to the light spot and move the first two weights an equal distance from it. If three weights fail to balance the driveshaft, replace the shaft.

14. When the driveshaft is balanced, road test the vehicle to verify the vibration is eliminated.

15. To evaluate all possible balancing alternatives, review the information found in the EVA Manual.