Diagnosis will be much easier once you have identified a vibration as first-order of driveline rotation during the road test. Next identify the exact area of the vibration 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, then evaluate the results during a road test. Many times, a vibration you were only able to reduce drastically in the stall will be completely eliminated on the road.

The cause of first-order driveline 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:

Caution: One or more of the following guidelines may apply when performing specific required tests in the work stall:

1. Raise the vehicle to curb height. Support the vehicle on a hoist or heavy stands. Refer to Lifting and Jacking the Vehicle in General Information.
2. Remove the rear tire/wheel assemblies, then install the wheel nuts to securely retain the brake rotors to the wheel hubs. Refer to Tire and Wheel Removal and Installation in Tires and Wheels.

Important: Do not step on the brake while the brake drums are being removed.

3. Remove the brake drums. Refer to Brake Drum Replacement in Drum Brakes.
4. Inspect the propeller shaft. The propeller shaft should be free of undercoating before continuing.
5. Inspect the propeller shaft and the U-joint for any obvious dents or damage. Dents or damage will contribute to first-order driveline vibrations.
6. Start the engine.
7. Place the transmission in gear.
8. Accelerate the vehicle to the speed at which the vibration was most severe.
9. Record whether the vibration was present, and at what speed.
10. If the vibration is not present, the vibration is most likely sensitive to torque. Refer to Diagnosis of 1st Order Vibration -- Torque Sensitive.
11. If the vibration is present, determine which end of the driveshaft is vibrating the most.

Important: Check to make sure the engine exhaust system is cool prior to placement of vibration sensor.





11.1.

Place the EVA vibration sensor on top of the rear axle differential, first at the rear (over the ring and pinion gear set), then move to the front (over the transmission output shaft at the transmission).

Important: Check to make sure the vibration sensor cord does not come in contact with the exhaust system during diagnostic testing.





11.2.

Using tie straps, strap the sensor cord out of the way.

11.3.

Accelerate the vehicle to the speed at which the vibration was most severe and check the EVA frequencies.

12. If the EVA is not picking up any high frequency readings to indicate a vibration concern, check the front bearing housing on the propeller shaft.

Important: Check to make sure the engine exhaust system is cool prior to placement of vibration sensor.





12.1.

Place the EVA vibration sensor on the front bearing housing assembly.

Important: Check to make sure the vibration sensor cord does not come in contact with the exhaust system during diagnostic testing.





12.2.

Using tie straps, strap the vibration sensor cord out of the way.

12.3.

Accelerate the vehicle to the speed at which the vibration was most severe and check the EVA frequencies.

13. If the EVA is not picking up any high frequency readings to indicate a vibration concern, check the rear bearing housing on the propeller shaft.

Important: Check to make sure the engine exhaust system is cool prior to placement of vibration sensor.





13.1.

Place the EVA vibration sensor on the rear bearing housing.

Important: Check to make sure the vibration sensor cord does not come in contact with the exhaust system during diagnostic testing.





13.2.

Using tie straps, strap the vibration sensor cord out of the way. Run the cord along the inside of the fuel tank strap and into the passenger door.

13.3.

Accelerate the vehicle to the speed at which the vibration was most severe and check the EVA frequencies.

If propshaft runout is suspected at this point, perform a driveline support assembly inspection. Refer to Driveline/Axle.

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

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. Refer to Tire and Wheel Removal and Installation in Tires and Wheels.
3. Remove the brake drums. Refer to Brake Drum Replacement in Drum Brakes.
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:

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.

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.