I know this should be posted in the main final drive thread.... but. This post from the LD board describes how to exchange the crown bearing and seal without removing the FD. Assuming the diagnosis made early.What do you think ?
From: "Dick Fish" <firstname.lastname@example.org>
Subject: [LDRider] BMW Rear Drive Bearing
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After some thought I will try to explain my experience with this BMW
weakness. I apologize in advance to all the non BMW riders on the list but
have been asked to add some details so will try to do the best I can for
those who care. For the people who know it all with Clymer manuals and the
"I've read or heard" knowledge or my mechanic "said" hit the delete key now.
I believe it is common knowledge that this bearing is a weak point in the
BMW rear drive. I presently own five BMW's of which four use the identical
bearing and seal. As I said earlier I have replaced three. As said very well
by David E.B. Smith the biggest problem is that most dealer's don't stock
the parts.If you carry them you eliminate this part of the problem. I also
agree with David's comment "If you have the bearing and
seals and can replace them before the whole drive gets trashed from lack
of oil and are mechanically skilled, you could handle probably 95% of
final drive failures."
This leads to catching the problem before it becomes more than the bearing
and seal. My experience indicates that a grinding noise will be audible
before you destroy the crown and pinion. Better than that is finding the
very small flakes of the inner race of the bearing before any noise starts.
You will find these on the drain plug magnet.These are extremely fine at the
beginning but the magnet shows that they are steel. If you remove and
examine the inner race of the bearing with a magnifying glass you will see
the initial breakdown. My answer to this is to change the rear drive
lubricant at every engine oil change which gives me the chance to inspect
the magnet. Very cheap insurance I believe.
Now to the interesting part that I'm supposedly not able to do.I believe
almost anybody can do this if they set there mind to it. I have a long
mechanical background so might have some advantage on some but this is not
rocket science.To clarify when I say on the road I would hope to be at a
service station at the least. You will need heat to accomplish this which
you must carry, buy, or borrow. A heat gun is the best but a propane torch
Remove the rear wheel and brake disk as required.
Using a 7mm Allen wrench ( which is not in the BMW tool kit and does
not come in most sets of metric Allen wrenches. I ordered mine separately
and carry one in each toolkit ,A long handle or socket driven works best.)
Remove the aluminium housing which carries the seal, bearing, crown gear and
Gently heat the aluminium housing around the seal. The crown gear, shaft,
and bearing will fall out of the housing with no help when the housing is
warm enough.Be careful not to let the crown gear fall and hit something.
There will be a shim or possibly two that is between the bearing and the
housing.This is what sets the gear lash in part and lets you replace the
bearing without redoing the gear lash if you accept the fact that the
tolerance on the bearing width is for these purposes identical.This part is
very easy because you are dropping steel out of aluminium.
The next is a little tougher because you are removing steel from steel.You
must heat the bearing while keeping the shaft cool. A wet rag on the shaft
after heating the bearing usually works. This is where I use the screw
driver unless I have a set of pullers to remove the bearing from the shaft.
The reassembly is much easier because you can heat the inner race of the
bearing while keeping the shaft cool. If at home I put the shaft in the
freezer and the bearing almost falls on. Make sure the bearing is fully
seated on the crown shaft At this stage remove the seal from the housing
and make sure the shim is replaced with the groove being perfectly clean.
Polish the end of the shaft where it is going to turn in the seal. Reheat
the housing and drop the shaft and bearing assembly into the housing making
sure it is fully seated against the shim. Replace the seal from the outside
being careful not to push it past flush with the housing. There is a small
o-ring around the outer edge of the housing that probably should be replaced
for good shop practice since it is a low cost item. Reassemble and you
should be good to go. If you are not comfortable with your torque skills
have the bolts re-torqued when a torque wrench is available. I hope this
does not sound complicated. I don't feel it is but others may have less
experience. At the very least I would carry the parts so a mechanic could do
this. If you feel comfortable with it I suggest you replace as described at
home and then carry the removed bearing and a new seal as your spares. Then
you will be confident on the road.
I hope this helps.