Rear Differential Axle Flange Seal Replacement

[Igor Kessel]

Folks,
I have just performed a Rear Differential Axle Flange Seal Replacement
on my
wife's '98 A4TQ. Perhaps somebody will find this write-up useful.
I have based this write-up on my old write-up for the UrS6, which in
turn was based
on the yet older excellent write-up for the 200TQ by Fred Munro.

Rear Differential Axle Flange Seal Replacement

1. Roll the front of the car onto the ramps. Jack up and safely support
the rear
of the car on jackstands making certain that the car is level. This will
become
important in step 17. I also removed the wheels because I wanted to
replace the
supper tyres with the winter ones, but I do strongly suspect that
strictly
speaking it is not really needed.

2. Loosen the filler plug on the rear differential with a 10mm Allen
socket.
Note that the A4 does not utilise the standard 17mm Audi Allen to which
you are
used so much. Loosen it before even attempting to loosen the drain plug.
You
don't want to be stuck with the empty differential facing the necessity
to turn
the car upside down for refilling if your filler plug is rusted in.

3. The best part is there is no need to remove the rear and the central
mufflers. The Bentley manual is wrong about that. I unbolted the two
beefy
exhaust mounts and carefully lowered it on the hydraulic jack as not to
strain
the EM studs. I then swung the whole exhaust 10-15 cm to the side and
that had
provided all the needed room for clearing the left axle.

4. Remove the bolt (the unusual for Audi 18mm hex!) that secures the top
of the
connecting link to the upper trapezoidal suspension arm and swing out
the lower
control arm with the connecting link. You might also need to remove the
bolt
that secures the rear stabiliser to that connecting link. This is
required to
release the inner CV joint and drop the half-shaft out of the way.

5. Remove the six 10mm triple square head bolts securing the inner CV
joint to
the axle flange. DO NOT use a Torx driver on these bolts - they take a
special
triple square driver. Make sure the driver is securely seated by
cleaning the
bolt sockets and tapping the driver home.

6. Remove the CV joint from the axle flange. This may take Croil or ZEP
or
Liquid Wrench if the car is old - rust between the joint and the flange
can bind
the unit together. Lower the inner end of the half shaft out of the way.

7. Remove the 6mm Allen head bolt securing the axle flange to the
differential
carrier - it is located in the centre of the axle flange. The axle
flange can be
held while removing this bolt by inserting a drift in one of the holes
to hold
the flange stationary.

8. In case you haven't lost as much oil as you think, put a drain pan
under the
differential. Pull out the axle flange. Inspect the seal running surface
for
wear and clean the flange & sealing surface.

9. Measure the old seal position with a caliper to determine how far in
it is
from the outer rim of the seal seat. There is no inner stop to position
the seal
- the Audi driver tool has an outer flange which hits the outer rim of
the seal
seat and stops at the proper depth. My both seals was seated at
approximately
7.8 mm from the outer rim given the parallax induced by my hanging
upside down
with a Mitutoyo calliper in my teeth.

10. Pry out the old seal with a seal remover. Wipe the seal seat clean.
Note
that it is tapered partway in but here is no inner flange to stop the
seal from
going too far. If you drive too enthusiastically, you can push the seal
right
into the dofferential - I can guarantee this will ruin your entire day!

11. You absolutely need at least a replica of the Audi tool. I've made
my own
version of the Audi factory seal driver 2062 out of Aluminium with a
flange
plate to stop the seal from falling in. You can try driving the seal in
w/o such
tool with just a hammer but I can almost guarantee you that you will
cock the
seal inside of the differential.

12. Fill the space between the lips of the seal with lithium general
purpose
grease. Put the seal onto the seal driver. Drive the new seal in
squarely to the
depth measured in step 9 above.

13. Apply a thin film of grease to the sealing surface of the axle
flange. Slide
the axle flange back into the dofferential. Insert the axle flange
securing
bolt. This bolt is tightened to 25 Nm. Always check your Bentley for the
actual
values since they can change at any point!

14. Bolt up the CV joint to the axle flange. It is recommended that the
gasket
between the axle flange and the CV joint be replaced whenever the joint
is
removed. I neglected to replace mine. The 10mm triple square bolts are
torqued
to 40 Nm.

15. Reinstall the bolt that secures the top of the connecting link to
the upper
trapezoidal suspension arm and tighten it up with a new nut. The torque
is 50 Nm
with additional 1/4 turn. Reinstall the bolt that secures the rear
stabiliser to
that connecting link and tighten it up with a new nut. The torque is 50
Nm.
Always check your Bentley for the actual values since they can change at
any
point!

16. Repeat the above for the other side.

17. Drain and fill the dofferential with appropriate lube. The Audi
specs call
for GL-5 spec 90 hypoid oil. GL-5 spec 80W90 hypoid is OK, as are GL-5
spec
synthetic gear oils. I personally like to use the Red Line synthetic
gear oil.
It's a good idea to put antiseize compound on the fill and drain plugs
to
prevent electrolytic corrosion between the steel plugs and the alloy
case.

18. Put on the wheels, torque the wheel bolts to 110 Nm and lower the
car.

Igor Kessel
08 December 2002
two turbo quattros