Vibrations

WARNING: THE ELECTRICAL POWER TO THE AIR SUSPENSION SYSTEM MUST BE SHUT OFF PRIOR TO HOISTING, JACKING OR TOWING AN AIR SUSPENSION VEHICLE. THIS CAN BE ACCOMPLISHED BY TURNING OFF THE AIR SUSPENSION SWITCH LOCATED IN THE RH KICK PANEL AREA. FAILURE TO DO SO MAY RESULT IN UNEXPECTED INFLATION OR DEFLATION OF THE AIR SPRINGS WHICH MAY RESULT IN SHIFTING OF THE VEHICLE DURING THESE OPERATIONS.

Driveline vibration exhibits a higher frequency and lower amplitude than does high-speed shake. Driveline vibration is directly related to the speed of the vehicle and is usually noticed at speeds of 72 km/h (45 mph) or higher. Driveline vibration can be perceived as a tremor in the floor pan or is heard as a rumble, hum, or boom. Driveline vibration can exist in all drive modes, but may exhibit different symptoms depending upon whether the vehicle is accelerating, decelerating, floating, or coasting. If the vibration is particularly noticeable during acceleration or deceleration, especially at lower speeds, the driveline angle should be checked. Driveline vibration can be duplicated by supporting the axle upon a hoist or upon jack stands, though the brakes may need to be applied lightly in order to simulate road resistance.

1. Raise the vehicle promptly after road testing. Use twin-post hoist or jack stands to prevent tire flat-spotting. Engage the drivetrain and accelerate to the observed road test speed to verify the presence of the vibration. If the vibration is not evident, check the non-driving wheels with a wheel balancer to rule out imbalance as a possible cause. If required, balance the non-driving wheels and repeat the road test. If the vibration is still evident, proceed to Step 2.
2. Mark the relative position of the drive wheels on the axle(s) or the wheel lugs. Remove the wheels. Install all the lug nuts in the reversed position and repeat the road speed acceleration. If the vibration is gone, check the wheel and tire assemblies. If the vibration persists, proceed to Step 3.

NOTE: Perform this procedure with the vehicle supported and all four tires off the ground.

3. Inspect the driveshaft(s) for signs of physical damage, missing balance weight, undercoating, or improperly seated, worn, or binding universal joints. Check the index marks (paint spots) on the rear of the driveshafts and axle(s) companion flange. If these marks are more than one quarter turn apart, disconnect the driveshaft and re-index to align the marks as closely as possible. Clean the driveshaft and replace the universal joints or replace the driveshaft if damaged. After any corrections are made, recheck the vibration at the road test speed. If the vibration is gone, reinstall the wheels and road test. If the vibration persists, proceed to Step 4.





4. With the vehicle on a hoist and the wheels off, measure the runout at the front, center, and rear of the driveshaft with indicator, rotating the driveshaft by turning a brake disc rotor. On a one-piece driveshaft, if the runout exceeds 0.89 mm (0.035 inch) at the front or center, the driveshaft must be replaced. If the front and center are within this limit, but the rear runout is not, mark the rear runout high point and proceed to Step 5. If the runout is within the limits at all points, proceed to Step 7 or the driveshaft balancing procedure.
5. Note or mark the indexing of the driveshaft to the axle companion flange. Disconnect the driveshaft, rotate one half turn, and reconnect. Circular axle companion flanges can be turned in one quarter increments to fine tune the runout condition; half-round axle companion flanges are limited to two positions. Check the runout at the rear of the driveshaft, if it is still over 0.89 mm (0.035 inch), mark the high point and proceed to Step 6. If the runout is no longer excessive, check for vibration at the road test speed. If vibration is still present, re-index the driveshaft slip yoke on the transmission output shaft one half turn and road test the vehicle. If the vibration persists, proceed to Step 7 or the driveshaft balancing procedure.

NOTE: Move the universal U-joints clockwise and counterclockwise during re-indexing. If a universal joint feels stiff or has a gritty feel in either direction, replace the universal joints.





6. Excessive driveshaft runout may originate in the driveshaft itself or in the axle(s) companion flange. To determine which, compare the two high points marked in Steps 4 and 5. If the marks are close together, within about 25 mm (1 inch), the shaft should be replaced and checked for vibration.





7. If the marks are on opposite sides of the driveshaft, the yoke or axle(s) companion flange is responsible for the vibration.

When replacing an axle companion flange, the driveshaft runout should not exceed 0.89 mm (0.035 inch). When runout is within limits, recheck for vibration at road speed. If vibration persists, balance the driveshaft.

8. To balance the driveshaft, install one or two hose clamps on the driveshaft, near the rear. Position of the hose clamp head(s) can be determined by trial-and-error.





9. Mark the rear of the driveshaft into four approximately equal sectors and number the marks 1 through 4. Install a hose clamp on the driveshaft with its head at position No. 1.

Check for vibration at road speed. Recheck with the clamp at each of the other positions to find the position that shows minimum vibration. If two adjacent positions show equal improvement, position the clamp head between them.





10. If the vibration persists, add a second clamp at the same position and recheck the vibration.





11. If no improvement is noted, rotate the clamps in opposite directions, equal distances from the best position determined in Step 8. Separate the clamp heads about 13 mm (1/2 inch) and recheck the vibration at the road speed.

12. Repeat the process with increasing separation until the best combination is found or the vibration is reduced to an acceptable level.
13. Install the wheels and road test, (vibration noticeable on the hoist may not be evident during the road test). If the vibration is still not acceptable, replace the axle drive line vibration damper first, if equipped. If the vibration is still not acceptable, replace the ring gear and pinion.