For 1990-2009 cars

## Driveline System Balance Adjustment Using EVA

This procedure is designed to fine-tune the balance of a drive shaft mounted on the vehicle. Small amounts of residual imbalance which could be present in other relative driveline system components could be compensated for as a result of performing this procedure. The end result of fine-tuning a drive shaft balance may be either a significant reduction or an elimination of a vibration disturbance that is related to the first order rotation of drive shaft.

Fine-tuning the balance of a drive shaft can aid in achieving a more balanced total driveline system.

Note: The drive shaft runout and runout of components that the drive shaft mates to must be within tolerances before performing this procedure.

#### Special Tools

• | J 38792-A Electronic Vibration Analyzer (EVA) 2

• | J 38792-20 20-Foot Timing Light Power Cord Extension

• | J 38792-25 Inductive Pickup Timing Light or equivalent

• | J 38792-27 6-Foot EVA Power Cord Extension

### Adjusting Procedures

Caution: Do not depress the brake pedal with the brake rotors and/or the brake drums removed, or with the brake calipers repositioned away from the brake rotors, or damage to the brake system may result.

1. Raise and support the vehicle; ensure that the drive axles are supported at ride height - vehicle body supported by suspension components. Refer to Lifting and Jacking the Vehicle.
2. With the tire and wheel assemblies, and the brake rotors and/or brake drums removed from the drive axle or axles, start the engine and turn OFF all engine accessories.
3. Set the transmission in forward gear.
4. Run the vehicle at the speed which causes the most vibration in the drive shaft, observe which end of the shaft exhibits the greatest disturbance.
5. Turn off the engine to slow and stop the drive shaft rotation.
6. Mark four points (2) 90 degrees interval at the circumference of the drive shaft (1) near the end that exhibited the greatest amount of vibration. Number the marks from 1 to 4.
7. Install the J 38792-A , the J 38792-27 , the J 38792-25 (or equivalent) and the J 38792-20 to the vehicle.
8. Connect the clip of the J 38792-25 (or equivalent) onto the trigger wire of the J 38792-A .
9. Mount the J 38792-A vibration sensor to the bottom of the driveline component nearest to the end of the drive shaft that exhibited the greatest amount of vibration.

Ensure that the side of the sensor marked UP faces upward and that the sensor is positioned as close to horizontal as possible.

10. Plug the vibration sensor cord into Input A of the J 38792-A . Input terminal B is not used with the strobe function simultaneously.
11. Run the vehicle at the speed which causes the most vibration in the drive shaft, observe the frequency readings displayed on the J 38792-A .

Note: Do NOT continue with fine-tuning the balance of a drive shaft if the dominant frequency displayed is not related to the first-order rotational speed of the drive shaft.

12. Check that the dominant frequency displayed on the J 38792-A matches the recorded frequency of the vibration concern.
13. Record the amplitude reading of the dominant frequency displayed.
14. Using the strobe function of the J 38792-A , select the correct filter range for balance adjustment, so that the dominant frequency would be near the middle of the filter range. Use the full range filter only as a last resort if one of the specific range filters will not cover the frequency adequately.
15. The J 38792-A will display the dominant frequency, the amplitude and the selected filter range.
16. Aim the J 38792-25 , or equivalent at the marks placed on the drive shaft. When the analyzer activated, the strobe effect will appear to freeze the marks placed on the rotating drive shaft. Record the number appears to be at the bottom of the drive shaft, or the 6 o'clock position. This position is identified as the light spot of the drive shaft.
17. Turn Off the engine to slow and stop the drive shaft rotation.
18. Install a band-type hose clamp as a weight, with the head of the clamp directly on the light spot.
19. Run the vehicle at the speed which can cause the most vibration in the drive shaft.
20. Using the J 38792-25 or equivalent, observe the position marks on the drive shaft.
21. If the drive shaft marks now move irregularly, then compare the current amplitude of the vibration frequency with the original amplitude recorded previously.

If the amplitude has decreased from the amplitude recorded, the balance achieved may be sufficient. The vehicle should be road tested to determine the effect on the vibration concern.

22. If the clamp head over the original light spot is now near the top of the drive shaft, away from the original position at the bottom of the drive shaft (6 o'clock) 180 degrees (near or below the 12 o'clock position), the weight position adjustment is necessary. Perform the following procedures:

22.1. | Move the position of the clamp head toward the 6 o'clock position.

22.2. | Using the J 38792-25 or equivalent, recheck the position marks on the drive shaft.

22.3. | If necessary, continue to move the position of the clamp head toward the 6 o'clock position and recheck the progress until an improvement in balance is achieved.

23. If the clamp head over the original light spot, is still positioned at the bottom of the drive shaft - 6 o'clock position - additional weight is required. Perform the following procedures:

23.1. | Add a second clamp to the drive shaft, next to the first clamp and with the clamp heads aligned.

23.2. | Using the J 38792-25 or equivalent, recheck the position marks on the drive shaft.

23.3. | If the clamp head over the original light spot is from the original position at the bottom of the drive shaft, are now 90 to 180 degrees-6 o'clock position, at or above the 9 o'clock or 3 o'clock positions-less total weight is required. Go to step 23.4.

23.4. | Move the clamp heads position an equal distance on either side of the light spot between 1 and 120 degrees intervals, to reduce the total amount of weight in relation to light spot.

23.5. | Use J 38792-25 or equivalent, recheck the position marks on the drive shaft.

23.6. | If necessary, continue moving the clamp head position an equal distance on either side of the light spot to a maximum of 120 degrees apart from each other, until the greatest improvement to balance is achieved.

23.7. | If the improvement has been made to the drive shaft but the balance is still unsatisfactory, still more total weight may be required. Perform the following procedures:

23.7.1. | Add a third clamp to the drive shaft, next to the first and second clamps and with the clamp heads directly on the light spot.

23.7.2. | Move the position of the first and second clamp heads an equal distance on either side of the light spot between 1 and 120 degrees apart from each other to arrive at a total amount of weight greater than two weights, but less than the three weights in relation to the light spot.

23.7.3. | Use J 38792-25 or equivalent, recheck the position marks on the drive shaft.

23.7.4. | If necessary, move the clamp head position of the first and the second an equal distance on either side of the light spot to a maximum of 120 degrees apart from each other, until the greatest improvement to balance is achieved.

23.8. | If a third clamp was used on the drive shaft and sufficient balance could still not be achieved, the drive shaft requires replacement.

24. If the clamp head over the original light spot is from the original position at the bottom of the drive shaft, are now 90 to 180 degrees-6 o'clock position, at or above the 9 o'clock or the 3 o'clock positons-less total weight is required Perform the following procedures:

24.1. | Add a second clamp to the drive shaft, next to the first clamp and with the clamp heads aligned.

24.2. | Move the clamp heads position an equal distance on either side of the light spot between 120 and 180 degrees interval, to reduce the total amount of weight in relation to light spot.

24.3. | Use J 38792-25 or equivalent, recheck the position marks on the drive shaft.

24.4. | If necessary, continue moving the clamp head position an equal distance on either side of the light spot to a maximum of 180 degrees apart from each other, until the greatest improvement to balance is achieved.

25. If the drive shaft marks now move irregularly, then compare the current amplitude of the vibration frequency with original amplitude recorded previously.

If the amplitude has decreased from the amplitude recorded , the balance achieved may be sufficient. The vehicle should be performed road test to determine the effect on the vibration concern.

## Driveline System Balance Adjustment Without EVA

This procedure is designed to fine-tune the balance of a drive shaft mounted on vehicle. Small amounts of residual imbalance which could be present in other relative driveline system components could be compensated for as a result of performing this procedure. The end result of fine-tuning a driveshaft balance may be either a significant reduction or an elimination of a vibration disturbance that is related to the first order rotation of drive shaft.

Fine-tuning the balance of a drive shaft can aid in achieving a more balanced total driveline system.

Note: Important: The drive shaft runout and runout of components that the drive shaft mates to must be within tolerances before performing this procedure.

### Adjustment Procedure

Caution: Do not depress the brake pedal with the brake rotors and/or the brake drums removed, or with the brake calipers repositioned away from the brake rotors, or damage to the brake system may result.

1. Raise and support the vehicle, ensure that the drive axle (or axles) are supported at ride height - vehicle body supported by suspension components. Refer to Lifting and Jacking the Vehicle.
2. With the tire and wheel assemblies, and the brake rotors and/or brake drums removed from the drive axle(s), start the engine and turn OFF all engine accessories.
3. Set the transmission in forward gear.
4. Run the vehicle at the speed which causes the most vibration in the drive shaft, observe which end of shaft exhibit the greatest disturbance.
5. Carefully hold a piece of chalk up to the end of the drive shaft to just make contact when the shaft rotates.
6. Turn off the engine to slow and stop the drive shaft rotation.
7. Observe the location chalk marked on the drive shaft.

• | If the chalk mark circles the entire drive shaft after the first attempt, remove the mark from the shaft and repeat the steps from 2 to 7, to allow the chalk touch more gently to the drive shaft.

• | If the chalk mark circles the entire drive shaft after the second attempt, then the drive shaft runout may not be the cause of the disturbance. Go to Step 16

• | If the chalk mark is only on a small portion of the drive shaft, the mark identifies the heavy spot of the drive shaft. The heavy spot of the drive shaft will deflect downward during rotation. Place a small mark on the shaft 180 degrees, directly opposite the heavy spot, and identify the mark as the light spot. Go to Step 8.

8. Install a band-type hose clamp to the drive shaft as a weight , with the clamp head on the light spot, or 180 degrees, directly opposite the heavy spot.
9. Observe the disturbance amount to the drive shaft.

• | If the disturbance amount to the drive shaft is significantly reduced, the balanced achieved may be sufficient and the vehicle should be road tested to determine the effect on the vibration concern. Move the clamp head slightly to refine the balance achieved, if necessary.

• | If the disturbance amount to the drive shaft appears to be almost unchanged or even increased, go to step 10.

10. Add a second clamp to the drive shaft, next to the first clamp and with the clamp heads aligned.
11. Observe the disturbance amount to the drive shaft.

• | If the disturbance amount to the drive shaft is significantly reduced, the balanced achieved may be sufficient and the vehicle should be road tested to determine the effect on the vibration concern. To get a more finest balance, move the clamp head position an equal distance toward the either side of the light spot, or move slightly together, with the clamp heads aligned.

• | If the disturbance amount to the drive shaft appears to be almost unchanged or even increased, go to step 12.

12. Move the clamp heads position an equal distance on either side of the light spot between 1 and 120 degrees apart from each other, to reduce the total amount of weight in relation to light spot.
13. Observe the disturbance amount to the drive shaft.

• | If the disturbance amount to the drive shaft is significantly reduced, the balanced achieved may be sufficient and the vehicle should be road tested to determine the effect on the vibration concern. If necessary, continue moving the clamp head position an equal distance on either side of the light spot to a maximum of 120 degrees apart from each other, until the greatest improvement to balance is achieved.

• | If the disturbance amount to the drive shaft appears to be almost unchanged or even increased, go to step 14.

14. Add a third clamp to the drive shaft, next to the first and second clamps and with the clamp heads directly on the light spot.
15. Observe the disturbance amount to the drive shaft.

• | If the disturbance amount to the drive shaft is significantly reduced, the balanced achieved may be sufficient and the vehicle should be road tested to determine the effect on the vibration concern. If necessary, continue to move the clamp head position of the first and the second an equal distance on either side of the light spot to a maximum of 120 degrees apart from each other, until the greatest improvement to balance is achieved.

• | If the disturbance amount to the drive shaft appears to be almost unchanged or even increased after a third clamp was used on the drive shaft, maybe the shaft replacement is necessary.

16. If the heavy spot on the drive shaft could be identified, install a band-type hose clamp to the drive shaft as a weight , with the clamp head directly in line with an existing factory-installed weight.
17. Observe the disturbance amount to the drive shaft.

• | If the disturbance amount to the drive shaft is significantly reduced, the balanced achieved may be sufficient and the vehicle should be road tested to determine the effect on the vibration concern. Move the clamp head slightly to refine the balance achieved, if necessary.

• | If the disturbance amount to the drive shaft appears to be almost unchanged or even increased, go to step 18.

18. Move the clamp head 180 degrees, directly opposite the factory-installed weight.
19. Observe the disturbance amount to the drive shaft.

• | If the disturbance amount to the drive shaft is significantly reduced, the balanced achieved may be sufficient and the vehicle should be road tested to determine the effect on the vibration concern. Move the clamp head slightly to refine the balance achieved, if necessary.

• | If the disturbance amount to the drive shaft appears to be almost unchanged or even increased, the drive shaft may need replacement.