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 Lifting and Jacking the Vehicle in General Information.
2. Remove the tire/wheel assemblies.
3. Remove and inspect 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 Kph (55 mph),accelerate from 72 Kph (45 mph) to 107 Kph (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 noise 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.