Audi Workshop Service and Repair Manuals

Adjusting crown wheel (Adjusting differential)   Note Re-adjustment of the crown wheel is required if the rear final drive housing, final drive cover, differential tapered roller bearings, differential cage or final drive gear set have been renewed. Table of adjustments → Chapter

Special tools and workshop equipment required

t	End measuring plate -VW 385/17-

t	Universal dial gauge bracket -VW 387-

t	Measuring lever -VW 388-

t	Crown wheel adjusting tool -VW 521-

t	Torque wrench -V.A.G 1331-

t	Dial gauge

t	Hexagon bolt M 8 x 45

Determining total shim thickness “Stotal” for shims “S1” plus “S2” (Setting preload of tapered roller bearings for differential) l  Pinion shaft is removed. l  If only the tapered roller bearings for the differential are being renewed, the crown wheel can be removed from the differential cage. The pinion shaft then does not have to be removed. l  Shims available for “S1” + “S2”: refer to → Electronic parts catalogue. –  Pry out flange shaft oil seal using assembly lever. –  Remove tapered roller bearing outer races for differential and take out shims → Chapter. –  Press outer race of tapered roller bearing together with a 1.00 mm thick shim onto stop in housing (S2 side) → Chapter.   Note For measurement purposes a 1.0 mm thick shim “S2” is inserted provisionally. This is referred to in the following as “S2*”. “S2*” is exchanged with the final shim “S2” after determining backlash.

–  Press outer race for tapered roller bearing without shim “S1” into cover for final drive. –  Fit differential in housing. Crown wheel is on same side as cover. –  Fit cover for final drive and tighten 4 bolts to 25 Nm in diagonal sequence.

–  Attach special tools to differential cage on final drive housing side. –  Turn final drive unit so that cover side faces upwards. –  Turn differential 8 turns in both directions to settle tapered roller bearings.

–  Attach measuring equipment. –  Place measuring plate -VW 385/17- on differential. A - Dial gauge extension -30 mm- –  Screw in hexagon bolt M 8 x 45-B-. –  Apply dial gauge extension to centre of measuring plate -VW 385/17-. –  Set dial gauge (3 mm measuring range) to “0” with 2 mm preload.

–  Raise differential in direction of -arrow- without turning, read play off dial gauge and note down (example: 0.50 mm). If the measurement has to be repeated, the differential must again first be turned 8 turns in each direction to settle the tapered roller bearings.    Formula: “Stotal” = “S2*” + measured value + bearing preload Example:

Example:
	Inserted shim “S2*”	1.00 mm
+	Measured value	0.50 mm
+	Bearing preload (constant value)	0.30 mm
=	Total shim thickness “Stotal” for “S1” plus “S2”	1.80 mm

Determining thickness of shim “S1*”   Note t  Provisional shim “S1*” is replaced with final shim “S1” after determining backlash. t  Total shim thickness "Stotal" remains unchanged.    Formula: “S1*” = “Stotal” – “S2*”

Example:
	Total shim thickness “Stotal” for “S1” + “S2”	1.80 mm
–	Inserted shim(s) “S2*”	1.00 mm
=	Thickness of shim “S1*”	0.80 mm

l  Select correct shim(s) from → Electronic parts catalogue.

Measuring backlash (Position of crown wheel in final drive housing) l  Pinion shaft installed with shim S3 l  Outer races for tapered roller bearings installed in final drive housing with shims S1* + S2* l  Differential installed –  Fit cover for final drive and tighten bolts to 25 Nm. –  Turn differential 5 turns in both directions to settle tapered roller bearings. –  Attach measuring equipment. –  Fit dial gauge with dial gauge extension -VW 382/10- (6 mm flat). Set measuring lever -VW 388- to dimension “a” = 60 mm. Measure play between teeth faces (backlash) as follows: –  Turn crown wheel until it makes contact with the face of one tooth (end of backlash travel). –  Preload dial gauge to 2 mm and set to “0”. –  Turn back crown wheel until it makes contact with opposite tooth face (backlash). –  Take backlash reading and note down measured value. –  Turn crown wheel through 90° and repeat measurements another 3 times. Determining average backlash –  Add the four measured values together and divide by four.

Example:
	1st measured value	0.28 mm
+	2nd measured value	0.30 mm
+	3rd measured value	0.30 mm
+	4th measured value	0.28 mm
=	Sum of measured values	1.16 mm

l  Result: the average backlash is 1.16 mm : 4 = 0.29 mm   Note If the individual measurements differ by more than 0.06 mm, this means that the installation of the crown wheel is not correct or that the final drive gear set itself is defective. Check installation; renew final drive gear set if necessary. Determining thickness of shim “S2”    Formula: “S2” = “S2*” – backlash + lift

Example:
	Inserted shim(s) “S2*”	1.00 mm
–	Average backlash	0.29 mm
+	Lift (desired average value for backlash)	0.15 mm
=	Thickness of shim “S2”	0.86 mm

l  For available shim(s) refer to → Electronic parts catalogue. l  The exact shim thickness required can be obtained by using the shim tolerance variations. Install two shims if necessary. Determining thickness of shim “S1”    Formula: “S1” = “Stotal” – “S2”

Example:
	Total shim thickness “Stotal” for “S1” plus “S2”	1.80 mm
–	Thickness of shim “S2”	0.86 mm
=	Thickness of shim “S1”	0.94 mm

l  For available shim(s) refer to → Electronic parts catalogue. l  The exact shim thickness required can be obtained by using the shim tolerance variations. Install two shims if necessary. –  Install correct shims: S1 on crown wheel side, and S2 opposite crown wheel. If necessary use 2 shims.

Checking adjustment –  After installing shims “S1” and “S2”, turn differential 5 turns in both directions so that the tapered roller bearings settle. –  Measure backlash four times on circumference. l  Specification: 0.12 ... 0.22 mm.   Note t  Adjustment must be repeated if backlash is outside tolerance. The total shim thickness “Stotal” must remain unchanged. t  The discrepancy between individual measured values must not exceed 0.06 mm.