Driveline vibrations can be related to one or more of the following components:

These components are splined together and therefore rotate at the exact same speed. This means that any vibrations they may cause will produce the same frequencies and the same symptoms. These vibrations will usually be related to the first-order of driveline rotation.

Driveline vibrations, as a whole, are vehicle-speed related. In many instances, the disturbance is also torque sensitive, meaning the vibration is present or more severe when accelerating, decelerating, or crowding the throttle. However, the disturbance will always appear at the same vehicle speed. This characteristic of being torque sensitive and vehicle-speed sensitive is always a clue in pointing to the driveline as a cause. (Tire and wheel vibrations are also vehicle-speed related, but are not torque sensitive, as a rule.)

The following are symptoms of first-order driveline vibration:

Once a disturbance has been identified as being related to the first-order of driveline rotation (during road testing), it is much easier to continue the diagnosis in the work stall. This allows for both identification of the exact area that the vibration is coming from and for proper action to then be taken. Of course this depends on being able to reproduce the same disturbance in the stall that was originally experienced on the road.

In most cases, the vibration can be reproduced in the stall, but it is either not as severe or a lot more severe than experienced on the road. This is normal. The idea at this point is to reduce the vibration to the lowest possible level in the stall and then evaluate the results on a road test. Many times a vibration that is reduced drastically in the stall will be completely eliminated on the road.

The cause of first-order driveline vibrations is usually due to excessive runout or the imbalance of a component. In order to quickly determine which component is at fault, the following procedure offers a systematic process of elimination.

Isolating the Components

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

•	When a test requires spinning the drive wheels with the vehicle jacked up, adhere to the following precautions:

-	Do not exceed 56 km/h (35 mph) when spinning one drive wheel with the other drive wheel stopped. This limit is necessary because the speedometer indicates only one-half the actual vehicle speed under these conditions. Personal injury may result from excessive wheel spinning.

-	If all of the drive wheels are spinning at the same speed, do not exceed 112 km/h (70 mph). Personal injury may result from excessive wheel spinning.

-	All persons should stay clear of the rotating components and the balance weight areas in order to avoid possible personal injury.

-	When running an engine in the repair stall for an extended period of time, use care not to overheat the engine and the transmission.

•	When a test requires jacking up the vehicle and running with the wheels and brake rotors removed, adhere to the following precautions:

-	Support the suspension at normal ride height.

-	Do not apply the brake with the brake rotors removed.

-	Do not place the transmission in PARK with the drive axles spinning.

-	Turn Off the ignition in order to stop the powertrain components from spinning.

•	When running an engine in the work stall, use the exhaust removal system to prevent breathing dangerous gases.

1. Raise and suitably support the vehicle on a suitable hoist or jackstands, so that the rear suspension is supported at curb height (with the rear wheels free to rotate). Refer to Lifting and Jacking the Vehicle in General Information.
2. Remove the rear tire and 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.

(Removal of the tire and wheel assemblies makes isolating the vibration easier.)

3. Check the propshaft for any undercoating and any obvious dents or damage to the propshaft or U-joints.
4. Start the engine and allow the engine to idle.
5. Have an assistant shift the transmission into gear, then run the vehicle up to the road speed at which the vibration was the most severe.
6. Note whether or not the disturbance is present, and at what speed it is present.
7. If the vibration IS present, determine which end of the differential housing is vibrating the most.

7.1.	Place the vibration sensor of the Smart EVA 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).

7.2.	Observe the frequency readings on the Smart EVA; the higher frequency readings will be seen closest to the disturbance.

8. If the vibration IS NOT present, the vibration is most likely sensitive to torque. Proceed to Diagnosis of First-Order Driveline Vibrations -- Torque Sensitive, below.

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 work stall, then it is possible that the vibration is being generated by internal rear axle components. This may also be true if the vibration was correctable in the work stall, but returned when the vehicle was driven on the road. These vibrations tend to be aggravated by the load of the vehicle working against the ring and pinion gear set.

Up to this point, the vehicle has been operated at a steady speed in the work stall where the vibrations seem to be the worst. This test is designed to load the pinion so it will produce the vibration on the hoist, allowing for identification and isolation of the vibration.

Isolating the Components

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

•	When a test requires spinning the drive wheels with the vehicle jacked up, adhere to the following precautions:

-	Do not exceed 56 km/h (35 mph) when spinning one drive wheel with the other drive wheel stopped. This limit is necessary because the speedometer indicates only one-half the actual vehicle speed under these conditions. Personal injury may result from excessive wheel spinning.

-	If all of the drive wheels are spinning at the same speed, do not exceed 112 km/h (70 mph). Personal injury may result from excessive wheel spinning.

-	All persons should stay clear of the rotating components and the balance weight areas in order to avoid possible personal injury.

-	When running an engine in the repair stall for an extended period of time, use care not to overheat the engine and the transmission.

•	When a test requires jacking up the vehicle and running with the wheels and brake rotors removed, adhere to the following precautions:

-	Support the suspension at normal ride height.

-	Do not apply the brake with the brake rotors removed.

-	Do not place the transmission in PARK with the drive axles spinning.

-	Turn Off the ignition in order to stop the powertrain components from spinning.

•	When running an engine in the work stall, use the exhaust removal system to prevent breathing dangerous gases.

1. Raise and suitably support the vehicle on a suitable hoist or jackstands, so that the rear suspension is supported at curb height (with the rear wheels free to rotate). Refer to Lifting and Jacking the Vehicle in General Information.
2. Remove the rear tire and 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.

(Removal of the tire and wheel assemblies makes isolating the vibration easier.)

3. Place the vibration sensor of the Smart EVA on top of the rear axle differential, at the rear (over the ring and pinion gear set).
4. Start the engine and allow the engine to idle.
5. Have an assistant shift the transmission into gear, then accelerate and decelerate the vehicle through the speed range at which the vibration was first noted during the road test.

Example: if the vibration was originally noted at 88 km/h (55 mph), accelerate and decelerate from 72 km/h (45 mph) to 104 km/h (65 mph), back to 72 km/h (45 mph) and so on.

6. Have the assistant repeat this process, while taking note whether the pinion gear set vibrates under load during the accel and/or decel.
7. If the vibration IS NOT experienced, reinstall the rear tire and wheel assemblies. Refer to Tire and Wheel Removal and Installation in Tires and Wheels.

(Reinstalling the tire and wheel assemblies will help to put an additional load on the system.)

8. Repeat the acceleration, deceleration process.

Notice: Do not accelerate against the brakes for longer than 10 seconds. Do not overheat the engine or the transmission. Depending on the vehicle design, the engine will only accelerate to a certain point under these conditions. Also, care should be taken during diagnosis as some disturbances may be created during brake torque that normally do not exist.

9. If the vibration still cannot be reproduced, try LIGHTLY applying the brakes to further load the system, while maintaining the vibration concern speed.
10. If during any of these steps, the area of the pinion gear set (the rear of the differential) produced the vibration, the rear axle differential will likely exhibit one of the following (or other abnormal) conditions:

•	A high spot on the pinion gear itself

•	A cocked or damaged pinion bearing

•	A mis-bored or mis-aligned axle housing, etc.

•	Bent pinion stem

Anything that can affect the pinion gear and how it contacts the ring gear as it rotates could contribute to a first-order, torque sensitive driveline vibration. The only way to correct for these conditions is to replace the affected components. In most cases this means the ring and pinion gear set and related bearings, but in some cases, it may include the axle housing. Presently, there is no way to effectively measure or identify the exact component at fault, except close visual inspection for unusual wear marks that may or may not be present.

Sometimes the installation of a known good axle assembly from a stock unit is the best way to quickly isolate an internal axle problem as the cause. Always qualify or evaluate the known good stock unit to ensure that it does not have a vibration problem.

Once an internal axle problem has been corrected, perform a road test, in order to determine if the vibration has been eliminated.

(1)	Inner Joint Outer Race
(2)	Inner Joint Cage
(3)	Inner Joint Inner Race
(4)	Ball Bearings
(5)	Inner Joint Outer Race Retaining Ring
(6)	Inner Joint Seal
(7)	Axle Shaft
(8)	Outer Joint

Rear-wheel-drive vehicles which utilize constant velocity (CV) wheel drive shafts do not typically experience many vibrations originating from the shafts.

CV wheel drive shafts used on rear wheel drive vehicles are always operating in a straight-ahead path (unidirectional), and therefore do not exhibit many of the conditions which can be found on CV-driven front wheel drive vehicles. There are, however, a few noise and vibration conditions which may occur; requiring diagnosis and correction.

•	High-frequency tire-related disturbances

•	Growing (wheel bearing) noise

•	Launch shudder

Launch shudder may also be heard as a droan or howl sound

Diagnosis of Launch Shudder and High-Frequency Wheel Speed-Related Vibrations

Launch shudder in a rear wheel drive vehicle may be felt as a shaking sensation in the steering wheel, the seat and/or the rear of the vehicle during moderate to heavy acceleration from a standing start. Launch shudder might also be described by a customer as a rocking back-and-forth motion in the vehicle during acceleration.

In rear-wheel-drive vehicles, launch shudder is typically caused by excessively worn or damaged wheel drive shaft inner CV joints.

Excessively worn, damaged, or imbalanced inner CV joints (enhanced double offset type) may cause launch shudder, but may be more easily detected as vehicle speed-related high-order vibrations.

If the inner CV joint is worn or damaged, the axle shaft (connecting the inner and outer CV joints) will NOT be rotating in balance, and will produce centrifugal force which may be felt, but will likely only be felt as launch shudder or high-order tire-related disturbance if the inner CV joint is EXCESSIVELY worn or damaged.

Momentary high-order wheel speed-related disturbances may be produced by excessive joint angles resulting from a powertrain mount that is damaged or misaligned.

Once the type of disturbance has been identified, visually inspect the wheel drive shafts for worn or damaged inner joints.

Diagnosis of Growling (Wheel Bearing) Noise

Rear-wheel-drive independent suspension hub and bearing assemblies can make a low, growling noise that increases with vehicle speed. Tires and bearings can make a similar noise and both are vehicle-speed-sensitive.

To differentiate between tire noise and bearing noise, drive the vehicle in a straight line and perform several turning maneuverers side-to-side. A worn wheel bearing will typically exhibit increased noise during turns. If the noise level increases during a right-hand turn, then the left-hand wheel bearing will generally be causing the problem. The opposite is true for a left-hand turn. If a bearing and not the tires is the cause of the disturbance, the noise level increases when turning because an added load is applied to the bearing at fault.