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Axle Noise Diagnosis

Part 5 - Axle Inspection and Analysis
From MasterTech October 1999
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Before you can perform any kind of axle service, you need to make sure you have all the required essential special tools (Fig. 11). It is important that these tools are inventoried and any missing or damaged items are ordered. A complete list of special tools required for each axle can be found in the differential and driveline section of the appropriate service information source.

Figure 11 - all of the essential axle tool are required for axle service. Inventory the tools before beginning service and replace any that are missing.

You will also need some other tools to complete the axle inspection and analysis, including a 0-1 " micrometer, and a 0-6" dial caliper (Fig. 12).

Figure 12 - A micrometer and dial caliper are used to make different measurements during axle adjustment and repairs.

Additionally, you will need a 0-75 inch-pound, beam- or dial-type torque wrench, as well as a 0-300 foot-pound torque wrench in Y4" or I " drive (Fig. 13). Heavy truck axles require a larger torque wrench.

Figure 13 - Inch-pound and foot-pound torque wrenches are also used.

The object of the axle inspection and analysis is to gather complete information about the axle to determine whether there is a gear, bearing, or runout issue within the differ- ential. We will go through each step in the process, but having the sound identified as a howl, growl or whine should give you an idea of what needs to be checked.

For example, a whine should get you thinking about checking the gear contact pattern and measuring back- lash, a growl will lead to checking for bearing preload or damaged bearings, and a howl indicates the need to verify proper runout of rotating components.

The February 1 997 Master Tech titled "Front and Rear Axle Service" is a very good reference for many of these axle service procedures.


To begin the inspection and analysis, remove the differ- ential cover from the axle that is exhibiting the sound. Inspect the condition of the-fluid (Fig. 14), looking for any obvious signs of degradation or axle failure.

Figure 14 - Inspect the fluid for signs of degradation or axle conditions.

Concerns can include fluid that is discolored, burnt or otherwise contaminated, or which shows the presence of metal filings. Always make sure that only manufacturer- approved fluids and additives are used.


Next you will need to measure the ring gear backlash, which tells you if the ring gear is positioned correctly in relation to the pinion. Use a dial indicator set against a ring gear tooth to make the measurement (Fig. 15). Measure and record backlash at eight to 16 points spaced equally around the ring gear.

Figure 15 - Set the dial indicator plunger against a tooth on the ring gear to measure backlash.

The backlash measurements should not vary by more than .002" from each other. If they do, the ring and pinion gear set or the differential case may be out of specification. For complete backlash measurement details and specifications, consult the appropriate service information source.


After removing the propshaft and both axle shafts, rotate the pinion at least 10 times to seat the bearings. Using a beam or dial-type inch-pound torque wrench, measure and record the total turning torque (Fig. 16). Make sure the rotation is smooth and steady. Uneven rotation can be an indicator of improper clearances.

Figure 16 Measure and record the total turning torque with an inch-pound torque wrench.


The next step in the axle inspection and analysis is a gear contact pattern check, which indicates whether or not the backlash and pinion depth are correct.

Paint the drive and coast sides of the ring gear teeth with Mopar gear marking compound. While placing a load on the pinion, rotate the ring gear one full revolution (Fig. 17), which forces the marking compound out of the areas with good contact.

Figure 17 - Rotating the ring gear while loading the pinion makes the gear contact pattern visible.

Observe the gear tooth contact pattern on the ring gear (Fig. 18) and compare it to the chart in the service manual or other service information source to determine if any adjustment is necessary. Then rotate the ring gear in the opposite direction and check the contact pattern again.

Figure 18 Compare the gear contact pattern to the chart in the appropriate service information source to evaluate ring gear backlash and pinion depth.


After checking the gear contact pattern, spread the housing on Dana axles no more than .020" with a spreader that is part of the axle service essential special tools (Fig. 19), and remove the differential carrier from the housing.

Figure 19 Use a spreader to spread the housing no more than .020".

Measure and record the pinion turning torque, in inch- pounds, with the beam or dial-type torque wrench. Subtract the pinion turning torque from the total turning torque to calculate the differential turning torque. Write this value down.

The next step is to remove the pinion gear and compare the match number on the pinion to the match number on the ring gear (Fig. 20). These numbers should be the same. If they are not, a new gear set should be installed.

Figure 20 - The match numbers on the ring and pinion gears should be the same.

Also record the pinion depth variance number that appears on the pinion, and remove the pinion depth shim (Fig. 21) and record its thickness.

Figure 21 - Record the thickness of the pinion depth shim.

Inspect all bearings and races (Fig. 22) for abnormal wear patterns or other signs of damage.

Figure 22 - Check bearings and their races for damage and excessive wear.

Then remove the ring gear from the differential carrier, and with the housing spread, install the carrier back into the axle housing. Remove the spreader after doing this.


With the carrier in the housing, measure and record the carrier runout at the ring gear flange (Fig. 23). Runout should be no more than .001". Measure the carrier runout again, this time at the flange center pilot, and record the value. It should be less than .001". If either runout measurement is out of spec, replace the differential case and bearings and verify proper runout.

Figure 23 - Measure carrier runout at the ring gear flange (shown) and at the flange center pilot.

Finally, using the appropriate special tools, measure to determine the proper thickness of the pinion depth shim (Fig. 25) and record this value.

Figure 24 - Measure to determine the proper pinion depth shim thickness.

Once you have completed the axle inspection and analysis and recorded all the required information, you can make a determination about what, if anything, needs to be adjusted on the axle to address the sound complaint. And that concludes Step 4 - isolating the condition. That takes us to Part 6 - making the adjustment.

Part 6 Service the Condition



Last Update: December 20, 1999