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Audi A8 Final Drive - Rear
Flange Seal Replacement
By Bob Dunne

Final Drive - Rear. Note oil and grime splattering on
adjacent support from a leaking output shaft seal.

The seals on the rear differential tend to leak on most A8's. Not enough to leave you stranded but enough to leave the differential and surrounding areas wet. This is a fairly straightforward fix. This procedure illustrates how to remove and replace the "output seals". These are the ones that face the CV axles. There is a third seal in the differential (it faces the driveshaft) but that is not covered here. That one can develop leaks as well. The procedure for the driver and passenger side is basically the same with some minor differences noted. If you have access to ETKA, take a look at illustration 525-20. Part # 12 on the diagram. If you have already done the prop shaft seal replacement, this will be an easy project for you.

Figure about 3- 3..5 hours to do both sides.

Parts Required
(2) flange seals, assuming that you do both sides. I paid about $12 for both. (Optional) - Audi gear fluid.

Tools Required

Get the car positioned (ramps, jackstand, lift) so that you have good access to the center of the car. Note: You will not have access to all of the axle bolts without either moving the car or rotating the rear wheel(s). I have a pit, so I just moved the car a few feet which rotated the axle and gave me access to the remaining bolts. You will have to reposition the car if you're using ramps. On jackstands, I suppose you could rotate the wheels and use the handbrake to lock the axle in place. No big deal, just something to keep in mind before you get all setup.

Using the 12 point socket, remove the six bolts that hold the axle to the differential flange (see note above, you will have to get the axle rotated in some way to get all six removed. Mark the axle and flange so that you can get it oriented the same way upon reassembly.

Now, gently pull the axle down and you will find a convenient holder in the emergency brake cable. You only need access to the center of the output flange to remove one bolt. You might have to move the CV joint around a little in order to get it to "clear" the lip on the flange. Just try a few different angles until it drops down and rests on the cable. If there is a lot of grease, put the CV joint into a big baggy and tie it shut while you do more prep work.

On the pass side, thread one of the bolts back into the flange all the way (remove the bag if you used one). You're going to use this in order to "lock" the flange in place so you can remove the center flange bolt. Move the flange so that the bolt bottoms out on the differential. There might be another/better way to do this but the flange bolt is very easy to remove so you're not putting much stress on anything.

Using a 6mm hex/socket, "lock" the flange as described above and remove the bolt directly in the center of the flange. It might not be obvious with all of the grease inside. This bolt is not torqued tightly so it should come out pretty easily.

Now, gently pull the flange straight out of the differential. Careful not to bang it and keep it clean. You will notice that virtually no gear fluid drips out at this point so it is unlikely that you will need any gear fluid to put back in. I checked the level when I was done and it was full. This is different than the prop shaft seal where quite a bit of fluid drips out when the flange is removed.

Clean the flange up where it contacts the seal. You can also polish it with very fine (#000) steel wool or similar. I also rubbed a thin layer of gear oil onto the surfaces that I cleaned up. Once that's done you are ready to remove the seal.

Look inside and you will see the source of your leak. Using a seal puller or something similar, remove the seal. Important:

Reinstall the new seal. Put a light coating of oil, gear oil, similar around the outside edge of the seal so that it slides in smoothly.

NOTE: You need something to seat the seal properly. I happen to have a 46mm socket which is the perfect size. Not everyone is going to have that laying around. You can use the back of a socket and gently tap around the outside edge to get it seated. Remember how far in it should go and don't put it in backwards.

Once the seal is in, reinstall the flange. Pay attention to your orientation marks and begin reinstalling the bolts. You'll have the same issue with access to all six as you did upon removal. Do whatever you did to get them out. I didn't find this in the Bentley (I'll keep looking) so I don't have torque values for any of the bolts. I'll update once I find them. I've done a millions axle replacements so I torqued these by feel along with the center flange bolt.

That's it, you're done !! Clean up everything, check the fluid level and test drive for leaks. If you're doing the drivers side as well, read below.

Driver's Side Notes
The drivers side is essentially the same with three exceptions:

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