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Audi A8 Transmission Output
Flange Seal Replacement
By Paul Waterloo

Symptoms of Seal Replacement
The transmission output seal is the seal that seals between the rotating output flange (which is bolted to the drive shaft) and the distributor gear chamber. This distributor gear is filled with gear lube, it has the gears that drive the the transmission output flange and the final drive - front, on the forward bottom side of the transmission.

The seal that rides on the output flange can leak gear lube across it. Once it drips out, it falls on the left side catalytic converter. This produces a nasty gear lube oil smell when it burns off. It is most noticeable during hot weather after shutting the car down. If you smell gear lube burning (it has a very distinct smell), this is most likely your problem.

If you get under your car, you'll be able to see burned oil on the left hand catalytic converter. That will confirm your problem.

Parts Needed
The 4 nuts, bolts and washers are to be used on the left hand side exhaust flange. The old hardware will be rusted and in need of replacement. I also purchased the exhaust donut which sits between the two flanges on the left hand exhaust, but it is most likely not needed. I did not use the replacement, the part is manufactured from steel, so it doesn't wear out.

Special Tools Required

If you don't have a lift, or access to a lift, you can complete this procedure, but it will be much more difficult. Find somebody with a lift to help you out!

Paul Waterloo's A8 on the way up to perform the job. If you don't have a lift, you'll need to put the jack up on four jack stands so you'll have clearance to drop the exhaust and fill the distributor gear.

Put the car up on a lift or jack the car up and place on four jack stands.

Pull the exhaust system from converters to tail pipes as an assembly. Disconnect at crossover immediately behind catalytic converters.

Using penetrating oil, spray all four nuts. Loosen nuts about 5 or 6 turns, but don't remove from bolts. Make sure you loose all four nuts, the pipes will seperate where they want to. Use smooth, even, torque on the nuts so they break loose, then let them stand for a minute or so before unscrewing them. This will prevent excessive heat build up in the bolt causing it to break.

Loosen all four nuts, this allows the exhaust to come off any of the four pipes when removing the exhaust.

Once all four nuts are loosened, open the clamps with a large screwdriver. With help of a friend, drop the exhaust by removing towards the rear. It is held up by four rubber hangers, it's best to spray with a soap solution and they just pop off with via hand pressure if you push up on the exhaust. If you are doing this on jack stands, place a jack under the exhaust and support it.

Pulling exhaust towards the back of the car, the exhaust pipes should pull out and move it out of the way.

The exhaust hangers just pop off with a little force. It's easiest to remove/install them by pushing up on the exhaust and sliding them off. Lubricate them with some soap solution for best results.

Remove the four left hand exhaust flange bolts. On the 97's it was a 13mm bolt head and a 12 mm nut, on the 98 it was 13 mm on both sides. If they strip, you can cut them with a sawsall. Use penetrating oil on the threads. The exhaust donut will fall out when they are removed. Move the cat off to the side and rest on something suitable so the O2 sensor does not have to be removed.

Left hand catalytic converter removed. What a nice design lift to do this job on! Rest it out of the way so the O2 sensor wire does not have to be removed.

Remove three heat shields, with the most forward one shown in the picture below first. They overlap forward to back. So when removing, remove the forward shield first. When installing, install the rear shield first. They are held in place with 13 mm nuts over studs, just bend them over the studs.

Remove heat shields (3) forward to back, install back shield to front. Note all the burnt oil on the bottom of the shaft output shield.

Remove the alloy front CV joint splash shield shown in the picture above. It is a Torx 45. Use a long extension to get to the two screws. Loosen one side, then loosen the other side, then remove the bolts, this will prevent movement of the shield protecting it from breaking during removal.

Loosen the driveshaft to output flange bolts, using a 6 mm hex on a 3/8" socket. If the wheels are in the air, use the parking brake to hold the drive train still.

Removing driveshaft to output flange bolts. Use the parking brake to hold the drive train in place if the wheels are in the air. The forward end of the drive shaft is actually a CV joint.

Gently tap the CV joint (forward end of drive shaft) with a rubber mallet to unseat it. Take care not to damage the flange gasket.

Remove the shield just aft of the drive shaft center bearing. Remove the center bearing shaft support, noting position of mounting and very carefully remove the drive shaft rearward. Support it with a piece of wire to the forward right exhaust hangers so it doesn't get damaged. It is carbon fiber and must be handled carefully. Keep exposed CV joints and flanges absolutely clean. Cover them with plastic bags if they will be left open for an extended amount of time. Do not wipe off the CV joint grease.

Remove shield and center support bearing. The center support bearing location should be noted prior to removal. You should be able to see the washer marks after removing it. Support it with a piece of wire to the forward right exhaust hangers so it doesn't get damaged.

Remove the final output flange using a Torx 40 socket. To hold the flange still while removing it, install two flange bolts and use a large screwdriver to hold the flange still. Before removing the flange, make sure you have an oil catch pan below, about 5 oz of gear lube will dribble out.

Use two bolts to hold output flange with a screwdriver when removing Torx bolt.

Pry out the seal using a screwdriver, take care not to score housing. Just bang on the screwdriver handle with your hand, using the housing as a fulcrum point.

Transmission output shaft seal after removing output flange. Make sure an oil catch pan is in place.

Remove the seal with a screwdriver.

Install the new seal flush to the housing. Tap in with a small hammer and seat with a large socket (1.5" or something suitable). Lube the inside diameter of the seal with a small amount of gear lube after it is installed.

Inspect drive flange. Polish seal surface with 1000 grit sandpaper or 0000 steel wool. Clean well. Reinstall flange and install center retaining bolt. Use lock tite on threads.

Clean the seal running area with 1000 grit sandpaper or
0000 steel wool to remove burnished area.

Remove the gear lube fill plug on the right hand side of the distributor gear with a 8 mm hex wrench. Open the gear lube bottle, it has a long nipple built in. Put the nipple in the distributor gear and fill the cavity until oil starts coming out, probably about 8 oz or less. Put the fill plug back in place and torque.

The Audi gear lube bottle has a built in nipple,
just squeeze the bottle and fill the distributor gear cavity.

Installation is reverse of removal. Torque the Torx bolt holding the output flange to 18 lb-ft of torque. Use new output shaft to drive shaft bolts. If using the old bolts, use loctite on them. Torque to 45-50 lb-ft.

Mount the rear support bearing in the same place as where it was removed.

When hanging the exhaust, first mount the left hand catalytic converter, and hand tighten the four flange nuts/bolts using new hardware. Then hang and mount the exhaust before tightening anything. After everything is in place, tighten all exhaust bolts. Use soap solution on hangers. Start car and ensure there are no exhaust leaks.

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