My rear differential seal started to leak a while ago, so did a re-search and couldn't find anyone doing DIY on A6, I did previously on my past A4's,
and the task wasn't difficult . I looked at the Bentley manual and there is little instructions provided, So here it is a DIY for seal replacement on A6
C5 Series. I have bought new drive axles seals and had left over Amsoil 75w90 Gear oil you need 1.5 Liters to fill it up, you can use any 75w90 synthetic oil found
at automotive store . The recommended replacement is every 100k miles or 60k miles to keep parts lubricated.
I did one seal at the time, at least one wheel has to be off the ground in order to move the axles around to access all the bolts .The rear muffler
needs to be dropped or remove from hangers this will give you enough clearance to move the axles to the side so you can remove the flange from the
differential (by manual they recommend dropping the catback exhaust , but it is not required )this will save you a lot of time, it took me 4 hours to do
one side the other was done in 70 minutes knowing all the steps, so with right tools you can do it under 3 hours.
Parts needed:
2 x 1 Liter 75w90 Synthetic Gear Oil
2 x rear differential seals (You need to order part for your car not 100% sure if the seals part# is the same for all the cars)
Tools / Cleaners I used:
12 point 8 mm key
10 mm hex key
8 mm hex Key
screw driver 8-10 long"
Engine Cleaner
Rubber mullet
oil transfer pump
Access to lift would be perfect, but i didn't have it, so I used scissor jack lift for big trailers rated at 7000 lbs and jack stands to stabilize the
vehicle rear end. I have lift the rear of the car with wheels off the ground which I needed to be moved freely to access the bolts, also I remove the rear muffler off the
hangers and support by jack stand
Here how my differential looked covered with oil
First task was to remove the heat shield that is attached to the rear differential, I used 8 mm key and removed the heat shield once that is done using
engine cleaner I cleaned every bolt from grease that needed to be removed Then first thing I did is to lose the fill and drain plugs , if you can't
remove the fill plug it will be hard to refill the differential.
Once you lose both plugs , then start removing the bolts from drive shaft using 8 mm 12 point key once that is done use rubber mullet and tap around the
driveshaft end to lose from flange move the driveshaft around it will come off , then pushed the end of the shaft toward the wheel, it will allow you to
pass over the flange and move the drive shaft toward the front of the car and let it
rest on the exhaust, you should have entire flange visible with half of inch clearance space between the flange and driveshaft clean the flange from the
grease and you will expose the securing bolt that hold the flange to the differential to lose the bolt use 8mm key and screw 2 bolts info flange shaft
and counter hold while unbolting the screw, then the flange will come off,
now you can see the seal,
clean the area of the grease, and using flat
screwdriver to carefully remove the seal take time, it is easy to damage aluminum ring and scratch it the walls where the seal sits ,
once that is done, clean entire seal area from grease,
then insert new seal, and using rubber mullet tap couple time once the seal gets half way, use your old seal and tap until the old seal is flash with
lip of the differential ring, as shown on the picture.
once that is done you are ready to put back everything, and do in reverse, clean the flange from
the grease and clean the ring where the seal sits, this is the residue left from leaking seal,
Install the flange shaft and tight the bolt to 25 nm
if you have shaft grease add about half of the bag into the flange, and install drive shaft into flange and tight each bolt 40 nm
re-install heat shield to differential and tight the bolts to 25 nm
Do the same process to other side , once you done, reinstall heatshield
Now it is time to drain the fluid , remove the drain plug, and let all oil drain to pan
it will be dark brown in color comparing to brand new oil.
once that's done, put back the drain plug and tight to 35 nm
open fill plug and using oil pump refill until it will fill to lower edge of filler opening.
once that is done, re tight the fill plug to 35 nm, clean residue left from leaking oil and put back the muffler into the hangers , and you are done.
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