Diagnosis will be much easier once you have identified a vibration as first-order of driveline rotation during the road test. Then identify the exact area that the vibration is coming from and take proper action.
In most cases, vibration may be reproduced in the stall. In the stall the vibration may be better or worse than that experienced during the road test.
The objective is to reduce the vibration to the lowest point possible in the stall, than evaluate the results on a road test. Many times, a vibration you were able to reduce drastically in the stall will be completely eliminated on the road.
The cause of first-order drive line vibration is usually excessive runout or an imbalanced component.
The following procedure offers a systematic process of elimination in order to determine which component is at fault:
Do not fill the propeller shaft with foam, oil, or any other substance in order to correct a vibration. Filling the propeller shaft is only effective in reducing an unrelated condition called Torsional Rattle. Filling the propeller shaft should only be done in strict adherence to the procedure outlined in corporate bulletins that address Torsional Rattle. Failure to follow the correct procedure will induce a vibration and/or affect the structural integrity of the propeller shaft. The propeller shaft will then have to be replaced.
A propeller shaft or pinion (companion) flange with excessive runout causes first-order driveline vibrations. Use the following procedure in order to measure runout of the propeller shaft (2). The tolerances are critical for smooth operation of the driveline.
• | Remove excess corrosion of the propeller shaft surface before checking runout. Also inspect for damage and dents. Replace dented propeller shafts. Remove any undercoating from the propeller shaft before proceeding. |
• | The measurement procedure that follows applies to all one-piece and two-piece propeller shaft assemblies. |
The splined end (1)of a propeller shaft is critical to the smooth operation of a two-piece propeller shaft. When checking stub-shaft runout, ensure that the dial indicator readings are accurate. |
• | J 8001 Dial Indicator Set |
• | J 7872 Magnetic Base Dial Indicator Set |
Do not include fluctuations on the dial indicator due to welds or surface irregularities.
5.1. | Rotate the propeller shaft 180 degrees in the pinion flange. Reinstall the propeller shaft and recheck the measurement. |
5.2. | If the runout still exceeds the tolerance, double-check the pinion flange runout before replacing the propeller shaft. |
6.1. | Measure the rear propeller shaft. |
6.2. | Mark the position of the rear shaft in the pinion flange, then remove the rear shaft. |
6.3. | Measure the front propeller shaft runout on the tube and the stub shaft. |
6.4. | Replace the propeller shaft if either measurement is out of tolerance. |
Refer to Propeller Shaft Runout Specifications
Important: When you replace a propeller shaft, check the new shaft for runout. Double-check the pinion flange runout if the replacement shaft runout is also out of tolerance.
• | J 8001 Dial Indicator Set |
• | J 23409 Dial Indicator Extension |
• | J 35819 Flange Runout Guage |
Important: The dial indicator will have inverted readings. You are measuring the inside diameter of the flange, and not the outside diameter. The highest reading on the dial indicator is the low spot. The lowest reading is the high spot.
• | If a J 35819 is not available measure the pinion runout as close as possible to the pinion flange. |
• | If necessary, add compensation weights on the face of the pinion flange dust slinger. These weights are tack-welded onto the slinger. You may remove the weights with a die-grinder. |
• | Carefully remove the spot weld at either end of the weight. |
• | Do not remove the weight unless you have inspected the pinion flange runout and the procedure calls for weight removal. |
• | Do not remove any weights on the outboard edge of the dust slinger. These weights are present in order to internal axle components. The weights are not related to the pinion flange runout. |
Most first-order driveline vibrations originate at the pinion nose end of the driveshaft. Ensure that the vibrations are at a minimum at this location in order to achieve acceptable results. Reduce the runout of the components to a minimum. Balance the driveline as a system when necessary.
Remove and reinstall the pinion flange only once on axles utilizing a crush type sleeve. Replace the sleeve with a new sleeve if the sleeve is crushed. Removing the sleeve requires removal of the ring and pinion set. Therefore, replace flanges with excessive runout. Regardless of the method used, measure the pinion flange runout in order to ensure that the flange is within tolerance.
First-order driveline vibrations that originate at the transmission end of the propeller shaft are rare. If the tailshaft of the transmission is vibrating, inspect the tailshaft housing bushing for wear or damage. A leaky transmission tailshaft oil seal indicates bushing problems.
Feel for vibration at the crossmember underneath the transmission mount. If there is no vibration, the transmission mount is doing its job of isolating the vibration from the structure of the vehicle. The transmission mount is therefore probably not cause of vibration.
Use the following procedure if you can feel vibration on the crossmember and the tailshaft bushing, and if transmission output is normal:
These guidelines apply to the two-piece propeller shaft only. First-order driveline vibrations that occur mainly at the center support bearing (2) are usually the result of excessive runout at the stub (splined) shaft (3).
Unlike other first-order driveline vibrations, these vibrations can appear at unusually low speeds of 40 km/h (25 mph) and up.
Follow the following procedure to correct this type of vibration:
Stub shaft/spline runout 0.076 mm (0.003 in)
Vibration is eliminated with the correction of the propeller shaft runout. If some vibration is still present, perform a vehicle road test. Then, determine if an on-vehicle system balance is necessary.
To pinpoint the source, you must reproduce the vibration in the service stall and then determine which component is vibrating the most using the EVA:
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.
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.
If the vehicle has a two-piece propeller shaft, check the center support bearing.
If the transmission tailshaft vibrates, check the transmission crossmember under the transmission mount. The vibration should not be present if the mount is doing its job.
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:
• | The differential housing |
• | The center bearing support (for two-part propeller shafts) |
• | The transmission tailshaft assembly |
The propeller shaft is balanced if the strobe image is erratic and the amplitude is near two.
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 between 90 and 180 degrees off (between the 9 and the 3 o'clock positions) too much weight exists. 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 between one and two weights (between 0 and 120 degrees apart). Inspect the balance again using the strobe light. Adjust the weights as necessary. |
• | The weight and original light spot are 90 to 180 degrees off (between the 9 and the 3 o'clock positions). |
The above 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 (between 120 and 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 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, then 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, then replace the propeller shaft.
When the propeller shaft balances, road test the vehicle in order to verify that the vibration is eliminated.
The following procedure is designed to fine-tune the balance of the propeller shaft while it is mounted in the vehicle. The procedure also is able 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.
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:
The last method involves road testing the vehicle at a speed which the vibration is felt.
If you performed the above procedure correctly, the chalk mark will indicate the heavy spot on the shaft. The heavy spot deflected downward and touched the chalk. If the chalk mark circle 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. Then perform the following steps:
If the vibration does not change at all, or gets worse, then one clamp is too light or too heavy.
• | If the vibration did not change at all, then repeat the procedure using two clamps together. |
• | If the vibration got worse, repeat the procedure using two clamps separated. Separate the clamps 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 three clamps aligned in the same position are required, then 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.
When using clamps in order to balance a propeller shaft with the total wight 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 clamp in order to accurately place any required amount between zero weights (0.0 total weight) to two weights (2.0 total weight).
The main objective of this section is to correct the conditions that interfere with the proper cancellation effect of the U-joints. The most common condition, especially where the where launch shudder is concerned, is incorrect driveline working angles. However, other factors may aggravate the condition.
Address these factors before you attempt to measure or correct driveline working angles:
• | Worn, failed, damaged, or improperly installed U-joints |
• | Worn, collapsed, or improper powertrain mounts |
• | Incorrect vehicle trim height adjustment for the front suspension. This condition aggravates launch shudder. |
• | Incorrect trim height adjustment for the rear suspension. |
• | Trim height inspection includes trim heights that are too low or too high. Vehicles equipped with aftermarket lift kits, vehicles that are constantly loaded with cargo, and custom conversion vans all fit in this category. On rear drive vehicles, the pinion nose tilts upward as the rear trim height is lowered. |
If a second-order driveline vibration exists after these conditions are corrected, measure and correct the driveline angles.
If the complaint is present only with cargo in the vehicle, perform the measurements with the vehicle fully loaded. Once a second-order driveline vibration has been corrected with the vehicle loaded, the vibration may reappear with the vehicle unloaded. The reverse of this is also true. You may have to reach a compromise with the customer in this case.
• | J 38460 Digital Inclinometer |
• | J 23498-A Driveshaft Inclinometer |
• | J 23498-20 Driveshaft Inclinometer Adapter |
Driveline working angle does not refer to the angle of any one shaft, but to the angle that is formed by the intersection of two shafts, as shown.
The procedure for measuring and correcting driveline working angles depends on whether the vehicle is equipped with a one or two-piece propeller shaft.
To verify the accuracy of the adapter, check the angle of an angle of an accessible joint with the inclinometer prior to assign it on an inaccessible joint.
Raise the vehicle on a suitable hoist or on safety stands. Ensure that the rear axle is supported at curb height and that the wheels are free to spin. Refer to Lifting and Jacking the Vehicle in General Information. Place the transmission in Neutral. Make sure the vehicle has a full tank of fuel or the equivalent amount of weight in the rear to simulate a full tank. 3.8 liters of gasoline (one gallon) weighs approximately 2.8 kg (6.2 lb).
Inspect the propeller shaft for correct phasing. This means that the front and rear U-joints are directly in line or parallel with each other so that proper cancellation takes place.
The out of phasing of the single-piece propeller shaft is very unusual. If the shaft is visibly out of place, the end yokes are welded on in the wrong position, or the shaft is damaged due to twisting. In either case, replace the propeller shaft before continuing with this procedure.
The working angle of a U-joint is the difference between the angles formed when two shafts intersect. One piece propeller shaft systems have two working angles, the front and the rear.
• | The two working angles should be equal within 1/2 of a degree. |
• | The working angles themselves should not exceed 4 degrees. |
• | The working angles themselves should not be equal to zero because a zero working angle will cause premature U-joint wear due to lack of rotation of the U-joints. |
The angle of the propeller shaft and the rear axle pinion form the rear working angle (2). The angle of the propeller shaft and the transmission output shaft form the front working angle (1).
The angles of these components are most accurately measured from the U-joint bearing caps. The bearing caps should be free of corrosion or foreign material to ensure accurate readings. Remove any snap rings that may interfere wit the correct placement of the inclinometer. Do not forget to reinstall them after you take the measurements.
Take the measurements from the same side of the propeller shaft to maintain consistent angle measurements (either driver or passenger side).
It is extremely helpful to record the readings on a diagram like the one shown as you proceed through the measurements.
The two working angles in a one-piece propeller shaft system should be equal to within 1/2 of a degree for effective cancellation.
Two-piece propeller shaft systems have three working angles instead of two as in one-piece systems.
• | The first angle is the front working angle (8). It is formed by the angle of the output shaft of the transmission (1) and the angle of the front propeller shaft (2). |
• | The second angle is the middle working angle (7). It is formed by the angle of the front propeller shaft (2) and the angle of the rear propeller shaft (4). |
• | The third angle is the rear working angle (6). It is formed by the angle of the rear propeller shaft (4) and the angle of the pinion yoke of the rear axle (5). |
This system has an odd joint that does not have another joint to provide cancellation. Therefore, the rear working angle (6) and the middle working angle (7) act as a pair of joints to cancel each other out, like in one-piece propeller shaft systems.
The front angle (8) is considered the odd joint because it does not have another joint to provide cancellation. Because of this, the working angle of the odd joint must be kept at or under 1/2 or a degree.
Keep the working angle of this odd joint to a minimum so that there are not any great fluctuations in speed that need to be canceled out. The front joint is used as the odd joint because the front joint angle does not change with suspension bounce, rebound, or axle windup. For this reason, think of the front propeller shaft of a two piece system as an extension of the transmission output shaft.
The setup and measurement techniques are identical to that of a one-piece propeller shaft system. First, check for proper phasing:
If the two U-joints of the front propeller shaft are not in this phase, the two halves of the propeller shaft may have been assembled incorrectly.
The procedure for lateral alignment of a two-piece propeller shaft is used for launch shudder or any second-order, driveline vibrations. Adjust the lateral alignment before you measure and adjust the driveline angles.
If launch shudder or second-order driveline vibration is still present, measure and correct the driveline angles.
This procedure is essentially the same as for one-piece propeller shafts. You must, however, take into account the third angle.
The working angle is within tolerance, following the rule that the working angle of an odd joint in a two-piece joint system is 1/2 degree or less. Notice that in each of the good examples that the front working angle (FWA) is 1/2 degree or less and is treated as a separate joint. The middle working angle (MWA) and rear working angle (RWA) are subtracted and the difference (DIFF) is 1/2 degree or less. The middle and rear joints may cancel each other.
In order to change the working angles, shim the components up or down. Look closely at the existing angles. Use the existing angles and the shims in order to achieve the correct working angles.
Compared to horizontal or true level, the components located at the rear of the vehicle are usually lower than the components located at the front of the vehicle. This condition is called down in the rear. If a component with a down in the rear angle is shimmed up at the rear, then the shim will bring the component closer to the horizontal (zero). Alternately, if a component with a down in the rear angle is shimmed down, then the component will move farther from the horizontal (zero).
Rear axle wind-up may cause launch shudder even when all of the working angles are within specifications. Rear axle wind-up occurs when heavy torque during acceleration causes the pinion nose to point upward. In order to compensate for axle wind-up, tip the pinion nose downward. Install the axle shims incrementally, performing a road test after each shim. Add shims until the road test indicates that the shudder is eliminated.
Wedge shims of different sizes are available through GMSPO and independent suppliers for the purpose of shimming the rear axle angle. GM shims are available in two, three and four degrees.
Caution: Never attempt to shim a rear axle using anything except shims that are designed for this purpose. Failure to do so will result in the shims falling out and a loss of vehicle control and that could cause personal injury.
Install the shims (5) in order to increase or decrease the angle of the rear axle pinion. Install the shims between the leaf spring (3) and the spring seat. Depending on the design of the suspension (leaf spring on top or underneath the axle), and the direction of the desired change, install the shims with either the thick side toward the front of the vehicle or toward the rear of the vehicle.
Important: After installing the shims, ensure that the U-bolt has two or three threads above the nut. Ensure also that the center bolt, located in the spring seat, is long enough to seat in the locator hole. If these two conditions do not exist, use longer U-bolts and center bolts. Longer U-bolts and center bolts are available through local spring shops.
If a transmission requires shims, order the shims through GMSPO.
Installing most shims will change the transmission angle approximately ½ degree.
When shimming transmissions, use a shim made from steel stock at the necessary thickness. Ensure that the shim contacts the full width of the area to be shimmed. Do not use washers.