For 1990-2009 cars

Front wheel drive shafts have the following characteristics

• | The front wheel drive shafts are short.

• | The front wheel drive shafts have constant-velocity (CV) universal joints.

• | The front wheel drive shafts have low mass.

• | The front wheel drive shafts turn or spin at a lower rate of speed than the propeller shaft on a RWD vehicle.

Although FWD is smoother than RWD, the following problem conditions may occur and require diagnosis and correction:

• | Launch shudder

• | Third-order tire-related vibrations

• | Growling (wheel bearing) noise

• | Clicking noise or shudder during turns

### Launch Shudder

Launch shudder is a shaking sensation that is felt in the steering wheel and/or the front of the vehicle during moderate to heavy acceleration from a standing start. Launch shudder may also be a rocking back-and-forth motion in the vehicle during acceleration.

On front-wheel-drive vehicles, launch shudder can be caused by the following conditions:

• | Worn or damaged inner tri-pot joints

• | Excessive inner joint angularity

Excessive joint angles are usually the result of a front trim or a spring height that is set too high. A powertrain mounting that is damaged or misaligned can also create the following conditions:

• | Excessive joint angles

• | Launch shudder

During fast acceleration, the front suspension height is raised by the high torque of the vehicle powertrain. When the suspension height rises, the inner tri-pod joint angles increase and can cause a launch shudder condition if one of the following conditions are present:

• | The joints are worn.

• | The angles are already excessive before acceleration.

Because the inner tri-pot joint is usually the cause of launch shudder, the disturbance is typically related to third-order tire rotation frequency.

1. Identify the type of disturbance.
2. Visually inspect the drive axles for worn or damaged inner joints.
3. If you detect no obvious problem, measure the trim or spring height in order to determine if the suspension is causing an excessive joint angle.

Do not measure the body height. Body height measurements are not used because potential sheet metal variations could lead to mis-diagnosis of the problem cause. Trim height specifications are found in the vehicle service manual.

4. If the spring height is out-of-specification, place sandbags under the following locations in order to lower the suspension:

• | Under the hood

• | Over the strut towers

Caution: Road test a vehicle under safe conditions and while obeying all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to these precautions could lead to serious personal injury and vehicle damage.

5. Road test the vehicle, adding sandbags until you eliminate the disturbance.
6. In order to lower the suspension, measure the spring height in order to determine the required springs to install.

Each vehicle line has multiple spring options with different spring rates. You can achieve approximately 10 mm of suspension height change by dropping down one spring code. You can locate the spring codes in the following areas:

• | On the springs

• | On the SPID label in the vehicle

Important: Always replace the springs in matching sets in order to insure correct body levels and proper suspension performance.

You can find the list of available springs in the parts catalog.

### Third-Order Tire-Related Vibrations

Tri-pot joints are so named because of their design characteristics. Tri-pot or tri-potal joints have three trunnions (or a trilobal spider assembly) that fit into a race or a cup. The assembly moves in and out freely in order to compensate for drive axle length changes during suspension travel.

Although worn or damaged inner tri-pot joints can cause launch shudder, worn or damaged inner tri-pot joints may also cause vehicle speed-related, third-order tire vibrations.

Third-order tire-related disturbances can occur if the following conditions are present:

• | The joint becomes worn or damaged.

• | The joint has excessive free-play or lash.

The worn joint creates three disturbances per revolution of the axle shaft. Because the axle shaft turns at the same rate as the wheel, third-order tire-related vibrations will result.

#### Growling (Wheel Bearing) Noise

Front-wheel-drive (FWD) hub and bearing assemblies can make a low, growling noise that increases with the vehicle speed. The tires and the bearings can make a similar noise. The tires and bearings are vehicle-speed-sensitive.

In order to differentiate between tire noise and bearing noise, drive the vehicle in a straight line and perform several turning maneuvers side-to-side. A worn wheel bearing typically exhibits increased noise during turns. If the noise level increases during a right-hand turn, then the left-hand wheel bearing generally is 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 with the fault.

#### Clicking Noise or Shudder During Turns

A clicking noise or a shudder during vehicle turns is usually a symptom caused by one of the following conditions:

• | A worn or damaged outer constant-velocity (CV) joint

• | A worn or damaged outboard CV joint

During a visual inspection of the drive axle, look for a damaged boot on the outer CV joint. A damaged boot can allow water and other contaminants such as dust and dirt to compromise lubrication and prematurely destroy the joint. The CV joint will no longer function smoothly, causing the disturbance.