Audi Workshop Service and Repair Manuals

(Adjusting differential)

The table on Page 39-64 lists the repairs which require adjustment of the crown wheel.

Determining total shim thickness "Stotal" for shims "S1" + "S2"

(Setting preload of taper roller bearing for differential)

• ● Drive pinion and differential removed.

• ‒ Take out old shims "S1" and "S2"=>Page 39-49.
• ‒ Fit 1.5 mm provisional shim "S2" (2 shims of 0.75 mm) in taper roller bearing outer race seat.

Note:

For measurement purposes a provisional shim "S2" of 1.50 mm is installed; this shim is designated "S2*" in the following. After determining the average backlash=>Page 39-96, "S2*" will be replaced by the correct shim "S2".

• ‒ → Pull outer race of taper roller bearing into gearbox housing onto stop with shim "S2*".

• ‒ → Press taper roller bearing outer race without shim "S1" into cover for differential.
• ‒ Fit differential into gearbox housing.
• ‒ Fit differential cover and tighten bolts to 25 Nm.

• ‒ → Secure dial gauge bracket VW 387 to housing and place end measuring plate VW 385/17 on differential.
• ‒ Preload dial gauge to 1 mm and set to zero.
• ‒ Move differential up and down several times without turning it.

Note:

Do not turn differential when measuring otherwise the bearing will settle and a false measurement will be given.

• ‒ Read off axial play on dial gauge and note reading.

• ● Reading in following example: 0.60 mm.

Determining thickness of shim "S1*"

Notes:

• ◆ The provisional shim "S1*" will be replaced with the correct shim "S1" after determining the backlash.
• ◆ The total shim thickness "Stotal" remains unchanged.

• ‒ → Press outer race for taper roller bearing with a shim "S1*" of the calculated thickness (1.00 mm in example) into cover for differential. Table of shims available for "S1"=>Page 39-101.
• ‒ Fit cover and tighten bolts to 25 Nm.

Adjusting backlash

(Setting position of crown wheel in gearbox housing)

• ● Drive pinion and shims "S3" and "S4" installed

• ‒ Install differential with shims "S1*" and "S2*".

• ‒ Fit differential cover and tighten bolts to 25 Nm.
• ‒ Turn the differential 5 turns in each direction to settle the taper roller bearings.
• ‒ → Secure dial gauge retainer VW 387 onto housing.
• ‒ Attach crown wheel adjusting device VW 521/4 and VW 521/8.
• ‒ Set measuring lever VW 388 to dimension "a" = 70 mm.

Measure play between teeth flanks (backlash) as follows:

• ‒ Turn crown wheel until it makes contact with one tooth flank (end of backlash travel).
• ‒ Preload dial gauge to 1 mm and set to zero.
• ‒ Turn crown wheel back until it makes contact with the opposite tooth flank.
• ‒ Read off backlash and note reading.

• ‒ → Fit separating device -A- (e.g. Kukko 17/2) if drive pinion turns whilst turning differential so that an exact backlash can be measured.
• ‒ Loosen locking screw of VW 521/4. Then turn crown wheel through a further 90°and repeat complete measuring process another 3 times. Add the four measured values together and calculate average backlash.

Determining average backlash

• ‒ Add the four measured values together and divide by four.

• ● Result: the average backlash is 1.96 mm /4 = 0.49 mm.

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 crown wheel and pinion themselves are defective. Recheck the installation, and if necessary renew crown wheel and pinion.

Determining thickness of shim"S2"

• ‒ Multiply the backlash figure by 1.17 (constant value), subtract the result from the thickness of the already inserted shim "S2" (1.50 mm in example), and add 0.20 mm for lift (constant value).

• ‒ Determine shim(s) as accurately as possible from table. Part numbers

=> Parts catalogue

The following shims are available for "S2"

    1)    Using the shim tolerance variations it is possible to find the exact shim thickness required, insert two shims if necessary.

Determining thickness of shim "S1"

• ‒ Determine shim(s) as accurately as possible from table. Part numbers

=> Parts catalogue

The following shims are available for "S1"

    1)    Using the shim tolerance variations it is possible to find the exact shim thickness required, insert two shims if necessary.

→ Carrying out measurement check - Measuring backlash

• ‒ After installing shims "S1" and "S2", turn differential 5 turns in both directions so that the taper roller bearings settle.
• ‒ Measure backlash four times on circumference.
• ‒ Specification: 0.15 ... 0.25 mm