Adjusting the circumferential backlash (transmission G 86)

The circumferential backlash must be 0.12 mm... 0.22 mm. 

1. Install the output shaft with the adjusting shims "S3" and "S4".
2. Insert the differential, fit the cover and tighten all fastening screws with the stipulated tightening torque.
3. Screw the special tool VW 388 to the special tool VW 521/4 and adjust the lever length to 72 mm with the gauge plunger. See Fig 1 .
4. Insert the adjustment device with the special tool VW 521/12 into the differential and clamp it securely.
5. Turn the differential several times in both directions so that the tapered roller bearings can settle.
6. Fit the dial gauge holder with the dial gauge so that a right angle is produced between the dial gauge axis and the lever.
   Fig 1: Fitting Dial Gauge Holder And Dial Gauge

   Courtesy of PORSCHE OF NORTH AMERICA, INC.

   Dimension "a" = approx. 72 mm

   Fig 2: Identifying Dimension "a"

   Courtesy of PORSCHE OF NORTH AMERICA, INC.
7. Carefully turn the crown wheel as far as it will go via the clamping screw of the adjustment device and set the dial gauge to zero. Next, turn the crown wheel back and read off the circumferential backlash. Note the value.
   NOTE:

   • If the friction coefficient of the output shaft is too low, the special tool 3177 must be fitted so that an exact circumferential backlash can be measured. The differential can then only be inserted in such a way that the aperture of the bevel gears faces the output shaft.
8. Repeat the measuring procedure another three times after continuing to turn the crown wheel through 90° in each case. Add up the measured values and calculate the average circumferential backlash. With the assembled special tool 3177, install the differential offset by 180° and repeat the measuring procedure.
   NOTE: If the individual measured values deviate from each other by more than 0.06 mm during this measurement, installation of the crown wheel or the drive set itself is not in order. Inspect the assembly work and replace the drive set if necessary.
9. Determine the average circumferential backlash.

   Example:

   CIRCUMFERENTIAL BACKLASH CALCULATION
   
   

   1st measurement		0.84 mm
   2nd measurement		0.85 mm
   3rd measurement		0.84 mm
   4th measurement	+	0.83 mm
   Total		3.36 mm
   Average circumferential backlash: 3.36 : 4	=	0.84 mm

10. Determining the disc thickness "S2" (with respect to the crown wheel).
    DISC THICKNESS (S2) MEASUREMENT CALCULATION
    
    

    S2	=	Stot.
    	-	Average circumferential backlash
    	+	Take-off (constant value)
    Take-off = 0.15 mm

    DISC THICKNESS MEASUREMENT CALCULATION
    
    

    Stot.		1.92 mm
    Average circumferential backlash	-	0.84 mm
    		1.08 mm
    Take-off (constant value)	+	0.15 mm
    S2		1.23 mm

    NOTE: Discs of 0.45 to 100.00 mm thickness are available (0.05 mm increments). Different tolerances allow the required disc thickness to be measured exactly.
11. Determining the disc thickness "S1" (crown wheel side)

    S1 = Stot. - S2

    Example:

    DISC THICKNESS (S1) MEASUREMENT CALCULATION
    
    

    Stot.		1.92 mm
    S2	-	1.23 mm
    S1		0.69 mm

    NOTE: Discs of 0.45 to 100.00 mm thickness are available (0.05 mm increments). Different tolerances allow the required disc thickness to be measured exactly.
12. Install determined adjusting shims "S1" on the crown wheel side and "S2" opposite the crown wheel.
13. Carry out a check measurement. When doing so, measure the circumferential backlash four times around the circumference. It must be 0.12...0.22 mm.