Initial Inspection and Diagnostic Overview

INSPECTION AND VERIFICATION
Vibration, roughness, tramp, shimmy and thump may be caused by excessive tire or wheel runout, worn or cupped tires, or wheel and tire imbalance.

These conditions may also be caused by rough or undulating road surfaces. Driving the vehicle on different types of road surfaces will indicate if the road surfaces are actually causing the condition.

1. Inspect for signs of uneven wear which may indicate a need for balancing, rotation, front suspension alignment, damaged tie-rod, or steering idler arm

2. Check tires for:
^ Cuts.
^ Stone bruises.
^ Abrasions.
^ Blisters.
^ Embedded objects.

3. More frequent inspections are recommended when rapid or extreme temperature changes occur, or where road surfaces are rough or occasionally littered with debris.
4. Tread wear indicators are molded into the bottom of the tread grooves. Replace tire when indicator bands become visible.

Do not immediately suspect the tires when attempting to diagnose a vibration concern. Other sources of vibration include:
^ Loose or worn wheel bearings.
^ Loose or worn suspension or steering components.
^ Brake hub and rotor or drum runout.
^ Loose engine or transmission supports.
^ Engine driven accessories.

ROAD TEST
A tire 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 tires.

If the road test indicates the vibration is related to the tires or wheels, refer to Pinpoint Test G under suspension testing and inspection.

If the road test indicates there is tire whine, but no shake or vibration, the noise originates from the contact between the tire and the road surface.

A thumping noise usually means the tire has flat or soft spots making a noise as they slap the roadway. Tire whine can be distinguished from axle noise because axle noise diminishes or changes according to load or speed. Tire noise remains the same over a range of speeds.

To verify that tire noise is not associated with shake or vibration, inflate the tires one at a time to 345 kPa (50 psi) and check for a change in the sound. The pitch or whine will change as the increased pressure changes the tire frequency.

CAUTION: Be sure to deflate tires to their proper pressures after this check is completed.