Adjusting ring gear

Determine total shim thickness "S tot" (Si + S2).

The ring gear must be readjusted if the transmission housing, transmission side cover, tapered roller bearings for differential, differential housing or drive set have been replaced.


The drive pinion must be removed in order to determine the preload of the differential tapered roller bearings.

1. Make sure the bearing outer races of the tapered roller bearings are well seated in the transmission housing or transmission side cover, respectively.

2. Fit one 2.5 mm spacer both on the ring gear side of the differntial to be used as well as on the opposite side.

3. Place differential into transmission housing and rotate repeatedly.

4. Fit transmission side cover without seal and tighten all bolts to 25 Nm.

5. Place gauge block plate VW 385/17 on the collar of the differential.

6. Fasten universal dial gauge holder VW 387 with dial gauge and extension to the housing and set to zero with 2 mm preload.

Measuring And Adjusting Backlash

A = Dial gauge extension (approx. 30...40 mm long)

B = Gauge block plate VW 385/17

7. Move differential up and down. Read off backlash on the dial gauge and note.


Do not turn differential while measuring backlash as this will give an incorrect reading.

8. Calculate "S tot".

"S tot" = thickness of inserted shims + measured value

+ pressure fit of tapered roller bearings


Thickness of inserted shims 5.00 mm

Measured value 0.90 mm

Pressure fit (constant value) 0.25 mm

"Stot" 6.15 mm

9. Remove differential, pull off both tapered roller bearings and distribute calculated shim thickness "S tot" as follows. As a start for backlash adjustment, the thickness of spacer Si is reduced by 0.70 mm while the thickness of spacer S2 is increased by 0.70 mm.

Rounded down ring thicknesses

Measure shims in several places using a micrometer. Admissible deviation is 0.02 mm. Also check shims for burrs and damage.


Total shim thickness of spacers Si + S2 = 6.15 mm

Thickness of spacer Si

6.15 mm

2.375 mm

Thickness of spacer S2

3.775 mm


The spacers are available in thicknesses of 1.6...3.1 mm in increments of 0.10 mm.

A 0.25 mm shim allows the ring thicknesses to be selected in increments of 0.05 mm.

The shim thicknesses calculated must be rounded up or down for plausible dimensions that will not alter the total shim thicknesses Si and S2.


Calculated ring thicknesses

39 - 22 Adjusting drive set

Porsche Classic Models

Porsche Classic Models

The History of Porsche Cars through its generational changes. A must have ebook for any Porsche fanatic, this ebook is a reference book for Porsche enthusiasts. Discover all there is to know about the greatest Porsches ever made. All models are fully described and illustrated providing a definitive production history plus an accurate guide to original specs and equipment.

Get My Free Ebook

Post a comment