Owners of 2004-2009 Audi A4/S4, 2005-2010 A6 and 2007-2010 A8 vehicles may report vibrations, humming noises or rubbing noises from the drivetrain when driving slowly around very tight turns. The noise is particularly noticeable when maneuvering at full steering wheel lock in a parking lot.
Friction-reducing additives in the differential oil are reduced by wear. At high load on tight turns, the friction discs and worm wheel teeth in the center differential are subject to wear. This changes the friction and locking values in the center differential and causes vibrations in the drivetrain.
Test drive the vehicle. Light vibrations at full steering wheel lock are normal. With stronger-than-normal vibrations in minor corners or heavy vibration at full steering wheel lock, proceed as follows:
- Check the center differential according to the repair manual for correct oil level and inspect for damage (metal shavings).
- Ensure that the wheels are not damaged (bent) and that all four tires are the correct size and type.
- If nothing is found, change the oil of the center differential with G 055 145 A2. The center differential does not have a drain plug. Gear oil must be drained by removing the cover. Follow the repair manual directions for removal and installation of the Self-Locking Center Differential Cover, but only remove the cover gar enough to drain the oil. Then reassemble and fill with the new G 055 145 A2 oil.
- Drive the vehicle along numerous bends until the gearbox temperature reaches 80 degrees Celsius (176 degrees Fahrenheit) and reassess the vibrations.
