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Axle Noise Diagnosis

Page 3 - Analyze the Symptoms
From Master TechOctober 1999
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You probably know that whenever gears are meshed together and moving, some level of sound is produced. Axle sounds are inherent to axle operation; excessive sound levels, on the other hand, mean that you may need to make adjustments to the axle.

Unfortunately, areas other than the axle can contribute to sound concerns (Fig. 9), including other driveline components, the engine and exhaust, and things like suspension and body components. This means you have to be especially careful before pinning the cause of a sound complaint on an axle. A good point to remember is that axle sounds can be classified into one of three main types: a howl, a growl or a whine.

Figure 9 Other components can contribute to the cause of sound complaints.


A howl is a low- to medium-frequency sound which may change in pitch, or have a rhythmic oscillation. A howl can usually be heard through all speed ranges and is torque-sensitive, and may be accompanied by a vibration. A howl is usually associated with excessive runout of rotating components.


A growl is a low-frequency sound that is nearly constant in intensity. A growl is not as torque-sensitive as a howl, but can also be heard through all speed ranges. A growl usually indicates a bearing issue.


The third type of axle sound is a whine, which is a high- frequency sound with a sharp, metallic quality. There is no oscillation to a whine, and it is very much torque- and load-sensitive. A whine is often speed-sensitive, meaning you can drive in and out of it, and is most prominent between 45 and 70 mph. A whine is usually the result of a ring or pinion gear issue.

So those are the three main types of axle sounds: howl, growl and whine. As stated earlier, however, components other than the axle can cause axle-like sounds, such as those in the driveline, the engine and exhaust, the suspension, body and others. An example of this is exhaust drone, which can easily be confused with gear whine, but can be heard while the vehicle is stationary. The point is, before you try to isolate the condition, you should have a good idea of whether the sound is a howl, growl or whine, which will lead you to check certain things.

In most cases, a howl is the sign of a runout concern in rotating components; a growl points to a bad bearing; and a whine indicates a gear issue.

Howl Runout of rotating components
Growl Bearings
Whine Gears


Part 4 Isolate the Condition



Last Update: December 20, 1999