Road Test

Road Test

Purpose of Road Testing

Important: Do NOT attempt to repair a normal condition, or the customer will probably be convinced that the vehicle has a problem. Customer satisfaction becomes extremely difficult after this point.


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 to the vehicle speed.

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

Determining the Component Group

After you have related a vibration to either the engine speed or to the vehicle speed, break the vibration down further in order to fit into one of the following groups of rotating components:

* The engine, the clutch disc (manual transmission), the transmission flywheel (automatic transmission), and the transmission torque converter.
* The transmission output shaft, the propeller shaft, and the rear axle differential pinion.
* The tires, the wheels, the hubs, the drums, and the rotors.

These three groups represent the major areas that can produce vibration complaints. The components in each group are related to each other because the components 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 in order to pinpoint the source and to eliminate unnecessary parts replacement.

Perform a road test for ALL vibration complaints unless the disturbance occurs only with the vehicle at a standstill.