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Axle Noise Diagnosis

Part 2 Verify Related Symptoms
From Master Tech October 1999
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VERIFY RELATED SYMPTOMS

Once you have verified that a sound exists, inspect the wheel and tire assemblies for any obvious signs of damage or uneven wear, and check for proper inflation pressure. Also make sure that all four tires are the same brand, model and size (Fig. 5).

Figure 5 Inspect the wheel and tire assemblies for damage or uneven wear; all four tires should be the same brand, model and size.

During the road test, note whether there are any vibrations associated with the sound and the suspected source. Also look for any issues with handling or braking, which could provide clues to the cause of the sound.

Repeat the drive mode and speed range tests at different engine speeds to determine if the powertrain is the source of the sound. This can be accomplished by switching the overdrive on and off (Fig. 6), or by manually downshifting a manual transmission. You can also change engine speed by lightly pressing the brake pedal. This disengages the torque converter for a minimal change in engine speed.

Figure 6 You can change the engine speed by flipping the overdrive on and off

If the sound changes with engine speed, it may be relat- ed to the engine and exhaust or the transmission (Fig. 7) - not the axles. If this is the case, note the approxiate engine speed at which the sound peaks.

Figure 7 Sounds that change with engine speed may be related to the engine and exhaust or the transmission.

Back in the service bay, check for any diagnostic trouble codes stored in the PCM, particularly if the vehicle exhibits performance concerns.

With the vehicle on a hoist, check for any loose or grounded items (Fig. 8), such as suspension or exhaust system components, which may be contributing to the sound.

Figure 8 Check for components that may be loose or grounded - in contact with other components.

Make note of any other symptoms associated with the sound, no matter how unrelated they seem. When it comes to sound complaints, the cause is often not readily apparent.

Part 3 Analyze the symptoms.


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Last Update: December 20, 1999