Front Diff (auto) driver side flange seal replace - looking for tips/clarification

[Rsniper4]

[Done, see comments for update]
Hello
My vehicle: 2001 A4, 1.8T AWD Automatic transmission,
I have sprung a moderate leak at the front differential on the driver side. I can't tell if the fluid is gear oil or transmission fluid...
I've replaced seals before, but I am seeking tips and/or clarification as to the proper procedure and what other components need to be removed/replaced when removing the flange. I've done prior research, but information is inconsistent and confusing.
Is it possible to simply slide out the flange, or does the entire flange housing (item 23) need to be removed with it? If the housing does indeed need to be removed, does the ball bearing (item 27) come out with it or does that remain in place deeper within the transmission? Does the ball bearing really need to be replaced like the manual states?
I've read that the gear oil must be drained from the front diff before removing the flange, otherwise it will mix with the ATF...? Is there any truth to this?
If ATF is leaking from the inside, then I'm guessing the internal o ring (item 29) needs to be replaced. I am doubtful this is the case since I have not read much about transmission leaks occurring in this area.

I really want to do this right so I don't damage any sensitive parts and prevent future leaks. I appreciate any and all help, advice, tips, and clarification!
Thank you!

George

Diagram.jpgitems.jpg

[Job complete, update in comments]

[PZ.]

Here is the DIY I made years ago. You will need to confirm any part numbers as this was a fwd trans.

http://passatb5.wikidot.com/automati...t-drivers-side

[walky_talky20]

I'd recommend you consult the Bentley version of this procedure. The one that PZ created is pretty great (the only writeup with pictures of this process that I've ever seen), but it skips over a critical step: draining the front differential gear oil.

The long axle shaft passes through the ATF chamber and then through a secondary internal seal where it passes into the differential section of the transmission. This seal separates the Gear Oil and ATF chambers. If you just yank the axle shaft out of the car, the gear oil can dump into the Auto Trans, immediately contaminating the ATF. Welcome to Slip City. So it is critical to drain the gear oil first before pulling the shaft out. As luck would have it, there is no drain plug for this. You have to suck the gear oil out through the fill hole. It's super great. Also critical is being *very* careful not to damage that internal seal at all when you are removing or reinstalling the shaft. It's located in the very depths of the transmission and damage will cause the gear oil and ATF to swap spit over time. No bueno (That means 'not good' in Spanish).

Anyway, I can email you the Bentley Manual pages that describe the procedure for changing this seal. Just shoot me your email address in a PM.

[Rsniper4]

Thank you PZ and walky for your contributions! I will be tackling this job on my next break! Will report back how it went...

[seanf86]

Double check its not the steering rack leaking directly above it and making it look like the axle seals leaking..... ask me how I know lol

[Rsniper4]

Job completed!
4 month update: procedure was completed successfully, everything fit back together and the leak has stopped.

I have used PZ's writeup and walky' bentley file info to complete this job successfully.
Since it was my first time doing a job like this, I decided to buy the backup hardware from ecs tuning. This actually saved my butt since I damaged the snap ring when attempting to remove it.

Part numbers:
- Snap ring (number 28 on diagram) MPN: 01V409297
- Bracket O ring (driver side, number 26 on diagram) MPN: 01V409133

I did determine that it was indeed transmission fluid leaking (I topped it off after ). I had found that the leak due to a worn o ring that seals between the transmission and the drive flange mounting bracket. The actual shaft seal was still looking healthy and was not leaking.
From the outside, it was too hard for me to tell that the leak was coming from the o ring, since the entire area was moist. I suppose going forward, if there is a leak in this area again, it would be good practice to replace both the flange seal and the bracket o ring.
Even though the bentley manual states to replace the drive flange ball bearing every time, I had found mine to be in excellent condition and did not warrant any replacement.
The snap ring that retains the flange to the bracket is rather tight, I ended up damaging mine due to improper tool use when removing. Luckily I had bought a spare one along with the replacement o ring. Placing the snap ring back luckily was considerably easier than removing it.

I hope this will help others that run into this issue down the road :)

[walky_talky20]

Wow, thanks for posting the update and all the detail. Interesting that the leak was just the o-ring.