Initial Inspection and Diagnostic Overview

A suspension vibration diagnostic procedure always begins with a road test. The road test and customer interview (if available) will provide much of the information needed to find the source of a vibration.

During the road test, drive the vehicle on a road that is smooth and free of undulations. If vibration is apparent, note and record the following:
^ the speed at which the vibration occurs
^ what type of vibration occurs in each speed range-mechanical or audible
^ how the vibration is affected by changes in vehicle speed, engine speed and engine torque
^ type of vibration sensitivity-torque sensitive, vehicle speed sensitive, or engine speed sensitive
^

Use the following explanation of terms to help isolate the source of the vibration.

Torque Sensitive
The condition can be improved or worsened by accelerating, decelerating, coasting, maintaining a steady vehicle speed and application of engine torque.

Vehicle Speed Sensitive
The vibration always occurs at the same vehicle speed and is not affected by engine torque, engine speed or transmission gear selection.

Engine Speed Sensitive
The vibration occurs at varying vehicle speeds when a different transmission gear is selected. It can sometimes be isolated by increasing or decreasing engine speed with the transmission in NEUTRAL or by stall testing with the transmission in gear. If the condition is engine speed sensitive, the condition is not related to suspension.

If the road test indicates the vibration is related to the tires or wheels, refer to Wheels, Tires and Alignment to help pinpoint the cause of the concern.