Torsional backlash, measuring

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Drive shaft installed with shims " S ₃ " and " S ₄ ".
O-ring is inserted in final drive cover.

Install differential with ring gear: " S ₁ " is on cover side, " S ₂ " is installed in transmission housing.
Install cover for final drive and tighten bolts to 24 Nm.
Insert locking sleeve VW 521/4 and VW 521/8.
Turn differential 5 turns in both directions so that the taper roller bearings settle.

Fig 1: Securing Dial Gauge Holder VW 387 To Transmission Housing

Courtesy of VOLKSWAGEN UNITED STATES, INC.

Secure dial gauge holder VW 387 to transmission housing.
Insert dial gauge with extension pin VW 382/10 (6 mm).
Set measuring lever VW 388 to dimension "a" = 75 mm (for ring gear dia. 186 mm).
Determine play between teeth flanks as follows:

Turn ring gear until it makes contact with a tooth flank (end of backlash travel).
Set dial gauge to "0" with 2 mm pre-load.
Turn ring gear back until lying against an opposite tooth flank (backlash).
Read off backlash and note measured value.

Turn ring through 90° and repeat measurements 3 times.

NOTE:

If drive pinion - 1 - turns when measuring, counter hold drive pinion so that an exact torsional backlash can be measured.

Determining average backlash

Add four measured values together and divide total by 4 to determine average.

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
=	Total of measurements	1.16 mm

Result: Average backlash is 1.16: 4 = 0.29 mm

NOTE:

If measurements vary more than 0.06 mm from each other, ring gear or gear set is not installed correctly. Check installation, replace final drive set if necessary.

Determining thickness of adjustment shim " S ₂ "

Formula: " S ₂ " = " S ₂ * " - measured torsional backlash + specified torsional backlash

Example:
	Inserted adjustment shim " S ₂ * "	1.30 mm
-	Measured torsional backlash	0.29 mm
+	Specified torsional backlash	0.15 mm
=	Thickness of adjustment shim " S ₂ "	1.16 mm

Available adjustment shims for " S ₂ "

Shim thickness (mm) * See note
0.45	0.61	0.77
0.49	0.65	0.81
0.53	0.69	0.85
0.57	0.73

*Using shim tolerances it is possible to find the exact shim thickness required, insert two shims if necessary.

Determining thickness of adjustment shim " S ₁ "

Formula: " S ₁ " = " S _total " - " S ₂ "

Example:
	Total shim thickness " S _total " for " S ₁ " + " S ₂ "	2.22 mm
-	Thickness of adjustment shim " S ₂ "	1.16 mm
=	Thickness of adjustment shim " S ₁ "	1.06 mm

Available adjustment shims for " S ₁ "

Shim thickness (mm) * See note
0.45	0.61	0.77
0.49	0.65	0.81
0.53	0.69	0.85
0.57	0.73

*Using shim tolerances it is possible to find the exact shim thickness required, insert two shims if necessary.

Fig 2: Securing Dial Gauge Holder VW 387 To Transmission Housing

Courtesy of VOLKSWAGEN UNITED STATES, INC.

Measurement check

After installing adjustment shims " S ₁ " and " S ₂ " , rotate differential 5 rotations in both directions so that tapered roller bearings settle.
Measure backlash four times on circumference.

Specified value: 0.12 to 0.22 mm

NOTE:

If drive pinion - 1 - turns when measuring, counter hold drive pinion so that an exact torsional backlash can be measured.
If backlash is outside tolerance, repeat adjustments. Do not change total shim thickness " S _total " while doing so.
The individual measurement values can deviate a maximum of 0.06 mm from each other