Front-wheel-drive (FWD) designs provide smoother drivetrain operation. Because of their design characteristics, front-wheel-drive vehicles generally do not exhibit many of the driveline vibrations seen with rear-wheel-drive vehicles. Typically front-wheel-drive axles are relatively short, have constant-velocity (CV) universal Joints, low mass, and turn or spin at a lower rate of speed than a propeller shaft on a rear-wheel-drive vehicle.

Although front-wheel-drive is generally smoother than rear-wheel-drive, certain problem conditions may occur and require diagnosis and correction. These conditions are:

Launch Shudder

Launch shudder is typically 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 might also be described by a customer as a rocking back-and-forth motion in the vehicle during acceleration.

On front-wheel-drive vehicles, launch shudder can be caused by worn or damaged inner Tri-pod joints and also by excessive inner joint angularity. Excessive joint angles are the result of a front trim or spring height that is set too high. A powertrain mounting that is damaged or misaligned can also crate excessive joint angles and cause launch shudder.

During heavy 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 lunch shudder condition, if the joints are worn or if the angles are already excessive before acceleration.

Because the inner Tri-pod joint is usually the cause of launch shudder, the disturbance will typically be related to third-order tire rotation frequency. For diagnosing the complaint, use the EVA in the Snapshot Mode or use a reed tachometer.

Once the type of disturbance has been identified, visually inspect the drive axles for worn or damaged inner joints. If no obvious problem is detected, measure the trim or spring height to determine if the suspension is causing an excessive joint angle. Refer to Trim Height in Suspension. 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.

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.

If the spring height is out-of-specification, place sandbags under the hood and over the strut towers to lower the suspension. Next, road test the vehicle, adding sandbags until the disturbance is eliminated. Then, measure the spring height to determine the required springs to install to the lower suspension.

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

Each vehicle line has multiple spring options with deferent spring rates. By dropping down one spring code, approximately 10mm (3/8 in) of suspension height change can be achieve. Spring codes can be located on the springs and also on the Service parts identification (SPID) label on the vehicle. The list of available springs can be found in the Service Parts Operation (SPO) parts catalog.

Third-Order Tire-Related Vibrations

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

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

Third-order tire-related disturbance can occur if the joint becomes worn or damaged and has excessive free-play or lash. The worn joint will create three disturbances per one revolution on 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 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. If a wheel bearing needs to be replaced, refer to Front Wheel Bearing and Hub Replacement or Rear Wheel Bearing and Hub Replacement in Suspension.

Clicking Noise or Shudder During Turns

A clicking niose or shudder during vehicle turns is usually a symptom caused by a worn or damaged outer or outboard constant-velocity (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.