Final Backlash and Carrier Bearing Preload Adjustments
After setting the pinion depth, backlash, and the pinion bearing preload, set the carrier bearing preload. Three different shim or adjustment methods, screw adjusters, outside shim design, and inside shim design, cover most differentials.
Screw Adjuster Design
The easiest method uses screw adjusters to set the backlash and carrier bearing preload. Carefully oil the adjuster threads on both the housing and on the adjusters themselves. Note the order in which you tighten the adjusters so the backlash remains consistent, even when subjected to heavy loads. The pinion gear always forces the ring gear away from itself whenever it transfers power. Start with a looser backlash setting than the axle’s manufacturer calls for and always ensure that the last adjustment made to the left adjuster tightens it. If the backlash becomes too tight, loosen the left adjuster first, followed by tightening the right adjuster. To reestablish the backlash setting, tighten the left adjuster. Ensure that the last adjustment made to the left adjuster tightens it to eliminate any space between it and its bearing race. Any space or looseness on the left side will let the carrier deflect when under load, and this will allow backlash to open up when driven under load. Once the backlash approaches the manufacturer’s recommendations, tighten both left and right adjusters evenly to increase carrier bearing preload. Set the carrier bearing preload to approximately 150 to 200 pounds/feet. It is difficult to damage bearings with excessive carrier bearing preload on a screw-adjusted differential.
If the preload is close and the backlash is too loose, tighten the left adjuster a notch or two until the backlash is correct and the preload is sufficient.
If the preload is close and the backlash is too tight, tighten the right adjuster until the backlash is correct and the preload is sufficient. As stated before, ensure that the last adjustment made to the left adjuster tightens it. That will eliminate the possibility of a space between the adjuster and the bearing race.
Outside Shim Design
This design uses shims between the carrier bearing races and the housing. Initially set the backlash with very little carrier bearing preload. After setting the backlash, add equal amounts of shims to both sides of the carrier to set the carrier bearing preload as tight as possible without damaging the shims (carrier bearings in this axle design hardly ever fail due to excessive carrier bearing preload).
If the preload is close and the backlash is loose, add shims to the left side. This increases the carrier bearing preload and tightens the backlash at the same time.
If the preload is close and the backlash is too tight, add shims to the right side. This increases both the carrier bearing preload and the backlash at the same time.
Inside Shim Design
This design uses shims between the carrier bearing and the case. Initially set the backlash tight and the preload light, as it will make carrier removal and installation easier. After setting the backlash, add equal amounts of shims to both sides until the correct preload is achieved. n If the preload is close and the backlash is loose, add shims to the left side. This increases the carrier bearing preload and tightens the backlash at the same time. n If the preload is close and the backlash is too tight, add shims to the right side. This increases the carrier bearing preload and the backlash at the same time.
Now that the pinion depth, pinion bearing preload, backlash, and carrier bearing preload are set, check the pattern one last time to make sure that it is correct.
When filling the axle with oil, use a high quality name brand and fill the unit to the manufacturer’s recommended capacity. Synthetic oil is recomended for most applications.
Backlash is the free movement of the ring gear with the pinion gear fixed in place. All ring and pinion sets are matched pairs. Make sure you have a matched ring and pinion set. Clean all parts before you start assembly. Apply a light coat of oil to all bearings. Examine all components and remove any burs, nicks or sharp edges that could cause components seat improperly.
1. Set backlash to proper clearance. (See page 11)
2. Shim or adjust the ring gear away from or closer to the pinion to get the correct backlash.
3. The pinion bearing preload should match those recommended on the specification sheet (See page 2). Achieve the recommended preload with a preload shim pack (combine shims of various thicknesses) or a collapsible crush sleeve. Use a new crush sleeve during final assembly.
4. Achieve the pinion depth by shimming the pinion toward or away from the ring gear centerline. Start with the same shim thickness on the new gear set as on the old set. Note that not all housings are shimmed in the same location.
Pattern Movements Summarized
1. Move the ring gear closer to the pinion to decrease backlash.
2. Move the ring gear farther from the pinion gear to increase backlash.
3. Move the pinion closer to the ring gear to move the drive the pattern deeper on the tooth (flank contact) and slightly toward the toe. The coast pattern will move deeper on the tooth and slightly toward the heel.
4. Move the pinion further away from the ring gear to move the drive pattern toward the top of the tooth (face) and slightly toward the heel. The coast pattern will move toward the top of the tooth and slightly toward the toe.
New Gear Break-In
All new gear sets require a break-in period to prevent overheating damage. Any overloading or overheating will break down the gear oil, which will cause the ring and pinion to fail. This can be determined by inspection and will void the gears’ warranty. Please follow these guidelines to insure proper break-in.
Avoid heavy acceleration during the break-in process.
Drive the vehicle lightly for the first 15 to 20 miles and stop. Let the differential cool before proceeding. n Avoid heavy acceleration for the first 100 miles.
Drive the vehicle at least 500 miles before towing to retain the gears’ warranty. n When towing for the first time, drive for a very short distances (less than 15 miles) with the full load and stop. Let the differential cool for about 20 minutes before proceeding. Repeat this procedure two more times (45 miles total) to fully break in the gears.
Change the oil after the first 500 miles. This will remove any metal particles and phosphoric coating shed by the gear set during the gears’ break-in period. These towing instructions may seem unnecessary to most people, but we have seen many differentials damaged from being loaded before the gear set was fully broken-in.