Side Bearing Preload & Ring Gear Backlash

After adjusting pinion shaft depth and bearing preload, remove front and rear covers from final drive housing. Withdraw pinion shaft. Install differential assembly and pinion shaft into final drive housing.
Install new oil seals into front and rear covers. Install new "O" ring on rear cover. Lubricate "O" ring and pinion shaft bearings. Apply sealer to bolt flange of front cover. Install front and rear covers and tighten attaching bolts.
Install new "O" rings on differential side bearing adjusting rings. Lightly coat "O" rings and threads on adjusting rings with multipurpose grease. Lubricate bearings with hypoid gear oil. Install each adjusting ring into housing until surfaces between tooth divisions are flush with housing surface.
Turn in right adjusting ring slowly until ring gear meshes fully with pinion gear without backlash. Screw in left adjusting ring (opposite ring gear) as far as possible. Preload left ring slightly to take play out of differential side bearings.
Turn right adjusting ring 1/2 tooth division out. Turn left adjusting ring 2 tooth divisions in. This should correctly set side bearing preload and ring gear backlash.
To check ring gear backlash, turn pinion shaft several times in both directions to settle bearings. Using Holding Fixture (VW 386a), clamp pinion shaft so that it cannot turn.
Insert Clamping Sleeve (VW 521/4) with Slotted Sleeve (VW 521/7 on 089 models; 521/8 on 087 models) into differential through adjusting ring and secure with nut. Adjust length of Backlash Measuring Bar (VW 388) to 2.44" (62 mm) on 089 models or to 2.68" (68 mm) on 087 models.
NOTE: See Fig 2 and Fig 3 for assembly and positioning of ring gear backlash measuring tools.
Attach Measuring Bar (VW 388) to Clamping Sleeve (VW 521/4). Install dial indicator with Square End Extension (VW 382/10) in Holder (VW 387) and attach holder to final drive housing.
NOTE: Dial indicator tip must be located at right angle to backlash measuring lever.

Fig 1: Adjusting Side Bearing Preload and Ring Gear Backlash
Courtesy of AUDI OF AMERICA, INC.

Use Spanner (VW 544) to turn adjusting rings.

Fig 2: Adjusting Measuring Bar Length for Ring Gear Backlash Check
Courtesy of AUDI OF AMERICA, INC.
Turn ring gear to take up backlash. Zero dial indicator and clamp in holder. Turn ring gear in opposite direction until it touches pinion gear again and note indicator reading. This reading is ring gear backlash.
Check ring gear backlash at 4 locations (90° apart) around circumference of ring gear. Add 4 measurements together, then divide total by 4. Resulting figure is average ring gear backlash. Average ring gear backlash should be .006-.010" (.15-.25 mm).
NOTE: Backlash specifications apply to new ring and pinion set. If ring and pinion are being reused, backlash should be set to same value as found prior to disassembly.

Fig 3: Positioning of Ring Gear Backlash Measuring Tools
Courtesy of AUDI OF AMERICA, INC.

CAUTION: Difference between individual backlash measurements must not exceed .002" (.05 mm). If measurements differ more than this, ring gear or pinion shaft is incorrectly installed.
If backlash is not within specification, correct by turning both side bearing adjusting rings by equal amounts in opposite directions. Adjusting rings must be moved in equal amounts to maintain bearing preload.
NOTE: If new differential side bearings have been installed, as well as new pinion shaft bearings, recheck pinion shaft turning torque. With differential installed, pinion shaft turning torque should be approximately 3.5-4.4 INCH lbs. (.4-.5 N.m) greater than it was when only pinion shaft was installed.
Install side bearing adjusting ring lock plate. Recheck total bearing preload to ensure no alterations were made during backlash adjustment. See Fig 1 .