For 1990-2009 cars

The techniques and procedures for correcting the following types of vibrations are including in the road testing diagnosis:

• | Tire and wheel shake

• | Steering/suspension shimmy and shake

• | Launch shudder

• | Exhaust moan

• | Engine firing frequency

### A Process of Elimination

A few basic concepts must be understood before attempting to diagnose a vibration. As in any diagnostic process, information must be gathered and deciphered, and a correction made based on the results. Road testing and inspecting the vehicle in a manner which systematically eliminates different components, in turn supplements the information received from the customer concerning the complaint. Concentrating efforts on the areas that have not been eliminated will make repairs faster and more effective.

### Duplicate the Condition

All vehicles produce vibrations. Some vibrations are normal, while others are not. Some vibrations can be repaired, some cannot. The customer's complaint must be duplicated or experienced. The vibration and the cause of the vibration must be evaluated under changing conditions. Otherwise, there is no way to know for sure that you are fixing what the customer would like fixed.

The symptoms and characteristics of a noise or vibration are also important information. Ask yourself the following questions before you begin:

• | What does the vibration feel like?

• | Does the vibration make noise? If so, what does the vibration sound like?

### What Does the Vibration Feel Like?

Different types of noise and vibration have particular characteristics. These characteristics will help determine the cause of the condition, and the best way to correct the condition. This is the reason for duplicating the vibration.

### Identifying the Complaint

The first step in diagnosing a vibration complaint is identifying the exact vibration that the customer is complaining about.

Sometimes the vibration can be duplicated at a given speed. Other vibrations may not be as evident and may require questioning the customer carefully. A road test may need to be performed with the customer in the vehicle in order to point out the specific vibration complaint.

The following questions should be asked when attempting to identify a vibration complaint:

• | At what speed is the vibration the worst?

• | Can the vibration be felt? If so, where?

• | Can the vibration be heard?

• | Does the engine or the vehicle load affect the vibration?

• | Does the vibration occur in more than one gear range?

• | When did the vibration first appear?

The answers to these questions will help in duplicating and diagnosing the vibration.

If the vibration that has been duplicated is suspected as being normal, compare the vibration with a vehicle that is equipped in the same way. The same equipment should include the following:

• | Body style

• | Engine option

• | Engine driven accessories

• | Transmission type

• | Tire size

• | Suspension performance type

• | Axle ratio

Important: Once an attempt has been made to repair what may be a normal condition, the customer will likely be convinced that the vehicle has a problem. Customer satisfaction becomes extremely difficult after this point.

If necessary, make the comparison with the customer present and explain the situation.

### Purpose of Road Testing

The purpose of road testing is to duplicate the vibration complaint and to find any operating conditions that change or eliminate the vibration. Most importantly, road testing will determine whether the vibration is related to the engine speed or the road speed.

In order to complete a quick and accurate road test, install an engine tachometer (such as a scan tool) and the EVA in the vehicle. Place the EVA vibration sensor in a location where the customer's concern can be felt.

### Which Component Group is Causing the Vibration

After a vibration has been categorized as being engine or vehicle-speed related, the vibration can be broken down further to fit into one of the following three groups of rotating components:

• | The engine, the clutch disc (manual transmission), the propeller shaft (within the driveline support assembly), the transmission flexplate (automatic transmission) and the transmission torque converter

• | The transmission output shaft and the rear axle differential pinion (mounted in the rear of the differential)

• | The tires, wheels, hubs, and rotors

These three groups represent the major areas that can produce vibration complaints. The components in each group are related to each other because they are either bolted or splined together. This means that each group of components rotates at the exact same speed.

These categories can be broken down further in order to identify the exact component responsible for the disturbance. The emphasis is on testing (and more testing) in order to pinpoint the source and to eliminate unnecessary parts replacement.

### Types of Road Tests

The following are the most often used and informative road test procedures:

• | Tire and Wheel Inspection

• | Slow Acceleration Test

• | Neutral Coast-Down Test

• | Downshift Test

• | Neutral Run-up Test

• | Brake Torque Test

• | Steering Input Test

• | Standing Start Acceleration Test (Launch Shudder)

Refer to

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.

in Cautions and Notices. These tests will help to pinpoint the vibration. Perform all of the tests on a smooth, level road.