Audi Workshop Service and Repair Manuals

Measuring backlash l  Pinion shaft fitted with shims “S3” and “S4”. l  The O-ring is fitted into cover for final drive. –  Install differential with crown wheel: “S1” is fitted on cover side, “S2” in gearbox housing. –  Fit cover for final drive and tighten bolts to 24 Nm. –  Insert crown wheel adjusting tool -VW 521/4- and -VW 521/8-. –  Turn differential 5 turns in both directions so that the tapered roller bearings seat properly.

–  Secure universal dial gauge bracket -VW 387- to gearbox housing. –  Fit dial gauge with dial gauge extension -VW 382/10- (6 mm flat). –  Adjust measuring lever -VW 388- to distance “a” = 75 mm (for Ø 186 mm crown wheel). –  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 a further 3 times.   Note If the pinion shaft -1- rotates during the measurements, counter-hold pinion shaft to make sure that the measured value of the backlash is correct. 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 from each other by more than 0.06 mm, the installation of the crown wheel or the final drive gear set itself is not correct. Check installation; renew final drive gear set if necessary. Determining thickness of shim “S2” Formula: “S2” = “S2*” - measured backlash + specified backlash

Example:
	Inserted shim “S2*”	1.30 mm
-	Measured backlash	0.29 mm
+	Specified backlash	0.15 mm
=	Thickness of shim “S2”	1.16 mm

–  Determine shim(s) according to table. Part numbers → Electronic parts catalogue “ETKA”. Available shims for “S2”

Shim thickness (mm) → Note
0.45	0.61	0.77
0.49	0.65	0.81
0.53	0.69	0.85
0.57	0.73

1)  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”	2.22 mm
-	Thickness of shim “S2”	1.16 mm
=	Thickness of shim “S1”	1.06 mm

–  Determine shim(s) according to table. Part numbers → Electronic parts catalogue “ETKA”. Available shims for “S1”

Shim thickness (mm) → Note
0.45	0.61	0.77
0.49	0.65	0.81
0.53	0.69	0.85
0.57	0.73

2)  The exact shim thickness required can be obtained by using the shim tolerance variations. Install two shims if necessary.

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. t  Specification: 0.12 ... 0.22 mm   Note t  If the pinion shaft -1- rotates during the measurements, counter-hold pinion shaft to make sure that the measured value of the backlash is correct. 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.