Part 2

Correcting Vibration at the Center Support Bearing

These guidelines apply to the two-piece propeller shaft only. First-order driveline vibrations that occur mainly at the center support bearing are usually the result of excessive runout at the stub (splined) shaft.


Unlike other first-order driveline vibrations, these vibrations can appear at unusually low speeds of 40 km/h (25 mph) and up.


Perform the following procedure in order to correct this type of vibration:

1. Mark the position of the rear propeller shaft at both ends for proper reassembly.
2. Remove the rear propeller shaft from the vehicle.




1 - Button Contact
2 - Center Bearing
3 - Stub Shaft

3. Measure the runout of the splines approximately 12.7 mm (0.5 in) from the end.
4. Replace the shaft if the runout exceeds the tolerances.
Stub shaft/spline runout 0.076 mm (0.003 in).


Correcting the stub shaft/spline runout will usually eliminate the vibration. If some residual vibration is still present, perform a road test on the vehicle. Determine if an on-vehicle system balance of the driveline is necessary.


Driveline System Balance without the Electronic Vibration Analyzer (EVA)

The following procedure is designed to fine-tune the balance of the propeller shaft while it is mounted in the vehicle. This procedure will also correct residual imbalance of the remaining driveline components.


Prior to balancing the driveline system, verify that the propeller shaft and the pinion flange runout are within specification.


Do not overheat the engine when performing this procedure.

1. Raise the vehicle to curb height. Support the vehicle on a hoist or on safety stands. Do not allow the axle to hang. Refer to Vehicle Lifting.
2. Remove the rear tire/wheel assemblies.
3. Remove the brake drums.
4. Determine which end of the propeller shaft has the most vibration in order to identify where to begin installing the hose clamps.




1 - Propeller Shaft
2 - Chalk Marks

5. Mark the end of the propeller shaft which has the most vibration at 4 points, 90 degrees apart. Number the marks 1-4.


The following procedure uses a trial and error method of determining where to place the hose clamps on the shaft. Use the following tips in order to help locate the clamps:

1. Because the imbalance may be related to propeller shaft runout, begin installing the clamps at the low point of the propeller shaft runout.
2. When the plant workers balance the propeller shaft, they use weights in graduated increments: 1/16 oz, 1/8 oz, etc. If the stock weight is too light or too heavy, place the hose clamp either directly in line with or opposite to the stock weight.


The last method involves running the vehicle at a speed which the vibration is felt.

1. Carefully hold a piece of chalk up to the very end of the propeller shaft. Barely touch the chalk to the shaft.
2. Shut the engine OFF in order to stop the propeller shaft from rotating. Do not step on the brake pedal. Do not put the transmission in PARK.
3. Inspect the chalk mark.


If you performed the above procedure correctly, the chalk mark will indicate the heavy spot on the shaft. The heavy spot will deflect downward and touch the chalk. If the chalk mark circles the entire shaft, touch the chalk more gently to the shaft. Ensure that the chalk touches only the heavy spot. Once the heavy spot is located, place the hose clamp 180 degrees opposite to the chalk mark. Perform the following steps:





1 - Balance Location
2 - Clamps Together

1. Place the hose clamp at the light spot, or at any of the 4 points marked previously.
2. Test drive the vehicle at the speed at which the vibration occurred. Record any changes in the vibration.
3. Move the clamp to the other positions.
4. Test drive the vehicle each time you move the clamp. Record any changes in vibration. Remember which position gives the best balance.


* If the vibration did not change at all or if the vibration becomes worse, then 1 clamp is either too light or too heavy. Repeat the procedure using the 2 clamps together.
* If the previous step did not correct the problem, repeat the procedure using the 2 clamps separated in order to reduce the spinning weight.


Continue the trial and error procedure using different weights in different locations until you achieve the best balance. If more that 3 clamps aligned in the same position are required, replace the propeller shaft.


If you are able to reduce the vibration in the stall, but are unable to eliminate the vibration completely, perform a road test on the vehicle. A slight vibration noticeable in the stall may not be noticeable on the road. Road Test


Driveline System Balance with Electronic Vibration Analyzer (EVA)

In order to pinpoint the source, you must reproduce the vibration in the service stall. Determine which component is vibrating the most using the EVA. Perform the following steps:

1. Support the vehicle on a suitable hoist or on safety stands. Ensure that the rear of the rear axle is at curb height. Do not allow the axle to hang. Refer to Vehicle Lifting.
2. Remove the rear tire/wheel assemblies.
3. Remove the brake drums.
4. Ensure that the propeller shaft is free of undercoating. Check for dents or damage to the propeller shaft or U-Joint.
5. Start the engine.
6. Place the transmission in gear.
7. Run the engine at the vehicle speed at which the vibration is occurring.


Caution: Do not run the vehicle higher than 89 km/h (55 mph). Stay clear of the universal joints and the balance weight area in order to avoid personal injury. Do not run the vehicle on the hoist for extended periods of time. Running the vehicle on the hoist for extended periods of time may cause the engine or the transmission to overheat.



If the vehicle has a two-piece propeller shaft, inspect the center support bearing.


If the transmission tailshaft vibrates, inspect the transmission crossmember under the transmission mount. The vibration should not be present if the mount is functioning correctly.


Determine which end of the propeller shaft is vibrating the most. Hold the EVA's sensor against the pinion nose and the transmission tailshaft assembly. The higher the amplitude reading, the greater the vibration.


Strobe Balance Testing with the Electronic 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.




1 - Propeller Shaft
2 - Chalk Marks

2. Mark the end of the propeller shaft that has the most vibration at 4 points, 90 degrees 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 B is 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. This 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.



1 - Balance Location
2 - Clamps Together

- If the weights are now 90-180 degrees 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 degrees apart). Inspect the balance again using the strobe light. Adjust the weights as necessary.
- The weight and original light spot are 90-180 degrees off (between the 9 o'clock and the 3 o'clock positions). This condition means that one weight is too much. In order to correct the balance, split the two weights equally on either side of the original light spot in order to produce a total weight less than one (120-180 degrees apart). Inspect the balance again using the strobe light. Adjust the weights as necessary.
- The weight and the original light spot are within 180 degrees 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 two conditions.




If the shaft will not balance using two weights, place a third weight on the light spot. Split the first two weights in order to produce a total weight between two and three weights.


If three 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.


Propeller Shaft Balance Weights

When using clamps in order to balance a propeller shaft with the total weight method, the correction weight required will often be a fraction or a multiple of one hose clamp. Use the following phasing procedure with two hose clamps in order to accurately place any required amount 0-2 weights (0.0-2.0 total weights).





1 - Balance Location
2 - Clamps Together
1. Ensure that the clamps are located with even spaces on either side of the light spot, or 180 degrees opposite the heavy spot.
The table containing the weight amounts in terms of the total weight and the included angle (spread) between the clamps is in specifications.
2. If the vibration does not change at all or gets worse, then one clamp is too light or too heavy. Repeat the procedure using the two clamps together.
3. If the previous step did not correct the problem, repeat the procedure using the 2 clamps separated in order to reduce the spinning weight.
4. Continue the trial and error procedure using different weights in different locations until you achieve the best balance.
5. If more than three clamps aligned in the same position are required, replace the propeller shaft.
6. If you are able to reduce the vibration in the stall, but are unable to eliminate the vibration completely, road test the vehicle. A slight vibration noticeable in the stall may not be noticeable on the road.



First-Order Driveline Vibration Analysis (Torque Sensitive)

If the following conditions are true, the internal rear axle components are the probable cause of the vibration:

* If the vehicle has a vibration that is equal to first-order driveline rotation, and the vibration is not present when testing the vehicle in the stall
* If you were able to correct the vibration in the stall, but the vibration returned during the road test


Internal rear axle vibrations may be aggravated by the load of the vehicle working against the ring and pinion gear seat.


Since the propeller shaft and the pinion gear are bolted together through the pinion flange, the propeller shaft and the pinion gear operate at the same speed. Vibration in the pinion gear will therefore have the same frequency and symptoms as the propeller shaft.


In order to isolate the vibration to the pinion gear, use the following procedure:

1. Raise the vehicle to curb height. Support the vehicle on a hoist or on safety stands. Refer to Vehicle Lifting.
2. Remove the tire/wheel assemblies.
3. Remove the brake drums.
4. Touch the pinion nose or hold the EVA vibration sensor up to the pinion nose.
5. With the aid of another technician, accelerate and decelerate the vehicle through the speed range at which the vibration was noticed during the road test.


Example
* If the vibration was originally noticed at 88 km/h (55 mph), accelerate from 72 km/h (45 mph) to 107 km/h (65 mph). Then decelerate from 107 km/h (65 mph) back to 72 km/h (45 mph).
* Repeat the above step and remember whether or not the pinion nose vibrates under load during acceleration and/or deceleration.



If the vibration does not occur during the above procedure, install the brake drums and the tire/wheel assemblies, adding additional load on the system. Then repeat the above test.


Ensure that both axle shafts rotate at the same speed. The differential may mask a vibration when one tire is spinning faster than the other tire. Adjust the brakes in order to correct unequal tire rotation speed.


If you are unable to reproduce the vibration in the stall, apply the brake lightly in order to load the system further. Maintain the vehicle speed at which the vibration was noticed. Do not overheat the brakes.


If the pinion nose vibrates under acceleration and/or deceleration, and the other driveline components are eliminated as the cause of the vibration, then one of the following conditions may cause the vibration:

* A high spot on the pinion gear
* A bent pinion stem
* A cocked pinion bearing
* An improper axle housing bore


Anything that effects the pinion gear and how the pinion gear contacts the rotating ring gear may contribute to a first-order, torque-sensitive driveline vibration. The only way to correct the condition is to replace the faulty components. In most cases, you must replace the ring and pinion gear set and the related bearings. In some cases, you must replace the axle housing. Complete a close-up visual inspection for damage or unusual wear in order to measure or identify the specific faulty component.


It is possible to isolate an internal axle vibration. Install a known good axle assembly from a stock unit. Verify that the known good axle assembly does not have a vibration problem.


Once you correct the internal axle problem, road test the vehicle. Inspect the vehicle for vibration. Balance the driveline, as necessary, in order to eliminate any remaining vibration.