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footyboyack
10-05-2011, 04:16 PM
Hi guys,

I have a '99.5 A4 B5 1.8T Quattro with the 5-speed Tiptronic. I notice moderate to heavy (like carshakingly heavy) vibration and accompanying low rumble noise when giving the car gas on a turn, from a standstill - as in accelerating when turning at an intersection. I have also noticed and examined an oil leak at the center differential, specifically at the output seal where differential meets driveshaft off the back of the transmission. Is my center differential failing? Are the gears becoming pitted, etc. due to heat from the supposed lack of oil within the diff.?

If so, how can I rectify the problem? I have a moly additive for differentials from Lubro Moly - will this help at all if I change the seal and fill the differential with oil+additive?

If the differential IS doomed, then does anyone know about sourcing a new one and what type of pricing I'm looking at?

Thanks for the time,
Ben P.

walky_talky20
10-05-2011, 04:21 PM
The vibration while turning is normal. I don't think it is anything to worry about. The leak is very common and needs to be fixed. Replace that output shaft seal and refill the center diff.

If it truly is "car-shaking", then you've got issues. Probably from running the diff out of oil. I do believe you can replace the center diff without removing the trans from the car. You just remove the tail section of the trans. You would definitely want to find used parts to fix it. The torsen center diff for the Tiptronic transmission is available as a separate piece from Audi at cost of over $1300.

If you end up needing those parts, PM me. I might be able to hook you up.

FNK
10-05-2011, 04:29 PM
Mine does the same thing, I also have a leaking center diff. (Fixing this this weekend)

But from what I've heard, it's just making it's job of transferring the torque between the front and the rear.

Edit :
Idiotic comment removed [facepalm]

walky_talky20
10-05-2011, 06:07 PM
Not hydraulic, it is just a gear package. No clutches or pressure applied besides the torque on the gears themselves. The binding is usually only noticed when turning quite sharply where the relative speed difference between the axles is at maximum. This is something that you don't really do at higher speeds. Pretty much just the parking lot and other tight turns.

footyboyack
12-13-2011, 09:22 PM
Thanks for the good advice, guys. I'm still not sure if I should put in the moly-additive or not, though. Common sense says I should be able to because it's certainly formulated not to harm seals, and there would be no issue with slipping clutches because, as walky_talky20 says, the differential is only a gear package. Any objections to putting in a bit of additive along with the fresh oil?

Thanks again,
Ben

walky_talky20
12-14-2011, 04:23 AM
I don't see any harm in putting in an additive. There is a friction element to how the torsen diff works. The friction between the components in the washer stack has some effect on the final TBR: Torque Bias Ratio (ie. how much "magic" the torsen is able to do). An oil additive may affect this somewhat. In your case that may be good because if anything it would smooth things out, possibly at the expense of a little TBR.

footyboyack
12-14-2011, 03:44 PM
Awesome, thanks.

pelletman
07-21-2013, 08:56 PM
Did you get the center differential problem taken care of? Can you share what it was? My don has an b5 a4 with the same issues, shuddering while turning and it is definitely NOT normal shuddering.. Thanks

footyboyack
07-26-2013, 04:53 AM
Did you get the center differential problem taken care of? Can you share what it was? My don has an b5 a4 with the same issues, shuddering while turning and it is definitely NOT normal shuddering.. Thanks

Hey pelletman,

I believe the shuddering was coming from the front or center diff, as I replaced the oil seals for both and refilled each with new oil and a moly additive, and the shuddering subsided to nearly nothing after a few days of driving and a few initial (I.e., post-fill) figure eights in a parking lot.

Best,
Ben