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TSB 03-05-99

Axle Diagnosis

Page 2 - Verify and analyze Symptoms

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VERIFY RELATED SYMPTOMS:

Areas other than axles can contribute to sound complaints. A four wheel drive vehicle will have additional sound paths, including other driveline components. This means that you have to be especially careful before associating the cause of the sound complaint with the axle.

1).    Continue with the Road Test. Determine that the noise is not being caused by related symptoms.

2).    To determine if the sound is engine speed related, drive in different gears when the noise occurs. For example: cycle the OD button to obtain a 4-3 and 3-4 shift without changing the throttle angle. Lightly depressing and releasing the brake pedal, while driving, will cause the torque converter to unlock and lock.

3).    Inspect vehicle for related vehicle vibrations, handling, and braking conditions' Inspect for any related diagnostic trouble codes (DTC's) which may be present.

Related symptoms that may be confused for axle noise are: Wind induced vibration (roof rack cross bars, loose body components, etc.)

Tire or wheel
Axle shaft bearing
Transfer case chatter/shudder
Axle chatter/shudder from the limited slip / Vari-Lok unit
Transmission overdrive unit chatter
Loose or grounded suspension components
Loose or grounded exhaust components
Loosed or grounded engine, transmission, transfer case components or mounts

4).    Stop the vehicle. Apply the parking brake. Place the transmission in NEUTRAL.

5).    Slowly increase the engine speed to the rpm range that the sound occurs. A drone sound can often be detected using this method since it is often engine speed related and is not axle related.

6).    Raise and support the vehicle in a safe manner.

7).    Inspect the vehicle powertrain and suspension for related conditions.

8).    If a related symptom is not the cause of the axle sound, then proceed with the DIAGNOSIS.

ANALYZE THE SYMPTOMS:

It is important to understand that all gears make sounds. Axle sounds are inherent. When a sound is perceived as a condition, by the customer, it becomes an issue that requires further investigation. The ability to identify the type of axle sound being generated will assist in determining what component of the axle will require service. There are three major types of axle sound: a growl, a howl, and a whine. Any axle may exhibit one or more of the sounds described in this TSB. It is very important for the technician to remember that the extent of repairs performed must address each of the sound conditions.

99 A growl sound generated by the axle may be caused by the contact surface of any bearing within the axle. This sound may occur when the surface of the axle bearing or the race becomes rough. The growl sound will tend to increase as the axle temperature rises and may increase as the bearing changes over time. The growl sound is often low in frequency and constant in intensity. The growl sound will occur through all speed ranges. Axle components that may generate this sound are a differential case bearing, a pinion bearing, or an outer axle shaft bearing. Exercising and/or loading the different bearings may assist in determining the affected component. Performing various turns with the vehicle is a method to exercise and load the outer axle bearings. If the axle is generating a growl sound then a visual and tactile inspection should be made of the contact surfaces of the affected component. Special attention should be paid to bearing preload and torque-to-turn values, as these indicators have a great impact on bearing life and sound.

A howl sound generated by the axle may be caused by runout of the major rotating axle components. This sound may oscillate rhythmically as the clearance between the rotating component change. The howl sound may be a low to medium frequency sound and may vary in pitch. A howl will be heard through all speed ranges, but can be torque sensitive. The vibration may accompany the howl and may be felt while driving in the pedals and steering wheel. Axle components may generate this sound are an out of round differential case, a pinion gear, or a ring gear. If the axle is generating a howl sound, attention should be paid to verify the runout for these major components.

A whine sound generated by the axle is very much torque and load sensitive. The whine sound is often a high frequency noise and does not oscillate. The whine sound will often be speed sensitive at one or more speed ranges. If the axle is generating a whine sound it may be due to reduced loads on the pinion or differential case bearings (preload). The low bearing loads may cause a change in the ring and pinion backlash and the contact pattern they create. Special attention should be paid to bearing preload, torque-to-turn values, and the contact pattern.

NOTE:    THE WHINE SOUND MAY BE CAUSED BY MACHINING VARIATION OF THE RING AND PINION GEAR SET. WHINE SOUND MAY BE CAUSED BY A RING AND PINION GEAR SET WITH A MACHINE VARIANCE EVEN THOUGH THE GEAR BACKLASH AND CONTACT PATTERN APPEAR ACCEPTABLE. IN THESE RARE CASES, THE TECHNICIAN WILL NOT BE ABLE TO DETERMINE VISUALLY THE MACHINING VARIATION AND CAN ONLY REPLACE THE GEAR SET TO ADDRESS THE WHINE CONDITION.

If the analysis is leading the technician toward a diagnosis that the condition is caused by an axle sound, then proceed with the ISOLATE THE CONDITION.

Page 3 - Isolate the condition

 


Thanks to Bob Bergevin for supplying the TSB information

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Last Update: October 25, 1999