Went to change rear tire on 99LT 60000+ miles. When I took out the studs that hold the wheel on, oil ran out all five holes.Not just a little, almost the entire final drive reservoir. Had replaced the bearing 15000 miles ago, it looks and sounds good. The outer seal is fine....and no oil residue anywhere on the wheel etc.


Any idea what has happened? How to remedy?

If you had oil out of the bolt holes removing the rear wheel bolts and you final drive is empty, the seal is NOT good. Did BMW replace the drive and was it less than two years ago? If so take it back to the dealer and have them replace the FD. There is not anyway that I know of for oil to leak out of the FD and it not be a seal issue. JM2CW

x2 on Steve.................It is a seal................

You had too much oil in the final drive. I'm surprised that you didn't have other signs of too much oil such as oil being vented out the breather.

What to do: clean up the mess.
Install your rear wheel.
Fill the final drive with appropriate lubricant up to the bottom of the threads of the filler hole. Do not spin the wheel to get more oil in, just let the oil settle until the level is even with the bottom of the threads. More than that is too much.
(You may find upon removing the final drive filler plug that you still have a little too much oil if you have not drained oil via the drain plug. Oil running out the wheel bolt holes will bring the level close to the proper level, but you may still have a little too much. I suggest draining the final drive via the drain plug and then refilling to the correct level).
Reinstall oil filler plug.
Go for a nice long ride.
Don't worry.

Explanation: The crown wheel assembly (which includes the hub the rear wheel is bolted to) is drilled and tapped all the way through for the wheel bolts. If you have too much oil it will come out those holes when you remove the bolts just as you observed. I was surprised when I first observed that the rear wheel bolts were involved in keeping the oil inside the final drive, but that is the way it is.

Replacing the crownwheel seal will have no effect on this. If the drive was not leaking before you removed the rear wheel, there is nothing wrong with your seal.

Charlie I think you meant to say.
Only the center bolt hole is tapped all the way through.

If you had oil out of the bolt holes removing the rear wheel bolts and you final drive is empty, the seal is NOT good. Did BMW replace the drive and was it less than two years ago? If so take it back to the dealer and have them replace the FD. There is not anyway that I know of for oil to leak out of the FD and it not be a seal issue.

According to the schematic, there is no seal other than the outer and inner housing seal. They have been replaced and there were no leaks around the housing. If you look in to the cluster (holes) from the wheel side you can see the ring gear moving and oil is present.

My understanding of the seals are they are to keep the oil contained in the housing? Both seals are on the outer housing. Is there a internal seal that keeps the oil from leaking to the bolt holes?

I always drain the final with the drain plug, so I am at a loss on how I overfilled it....never have had any issues in the past.

Please keep the answers coming, I appreciate it!

Well, sort of but not exactly. To clarify: The outer holes do communicate with the inside of the FD housing (on at least some of the crownwheel hubs I have seen.) The outer portion of the bottom of the outer wheel bolt holes is bottomed in the body of the hub. The inner portion of the bottom of the outer wheel bolt holes is bottomed by the aluminum component of the crownwheel assembly. Note that crown wheel assembly is made up of two components, one carbon steel, the other aluminum, which are pressed together. This assembly comes from BMW as one part. And there is a small gap there that will let oil out. If you just sound the bottom of the outer holes you would conclude that they are solid at the bottom. But they are not.

In a little while I'm going to go pop open my spare FD and take a few pics. I'll reply more after that. Meanwhile, don't throw away your final drive.

I am still learning here; my previous answer about too much oil was based on what I recalled of the machining of the crownwheel hub. So much for going on memory!
Now I am curious what the inside of your drive looks like.
Attached here are some pics of my spare which I just opened.

One pic shows the hub with bolt holes. I think you can see the bottom of the outer holes where the bottom is partly the metal of the carbon steel hub and partly the pressed in aluminum component of the crown wheel assembly. There is a small space at the bottom where the bolt hole communicates with the cavity inside the aluminum casting of the crown wheel assembly. If I shine a light down one of the four outer bolt holes, I can see the light through the center bolt hole; all the bolts hole communicate with the cavity in the center of the aluminum casting.

However, what I don't see on this particular assembly is how oil from the oil bath would get into this cavity inside the crownwheel assembly. This is why I wonder what your crownwheel assembly looks like. How did oil from the housing get inside the cavity of the crownwheel assembly I wonder?

It was reported in BMW Owner's News (Max Parkhouse's column IIRC) at least one case of FD failure where the aluminum component was not properly fitted to the crown wheel hub. This resulted is symptoms of final drive failure, not what you are reporting; but the report gets me wondering. It seems to me that the obvious conclusion is that there is a communication between the cavity inside the crownwheel assembly and the oil bath, but where it is, or if it is of any significance remains a question.

Why don't you open up the drive and have a look? And take some pictures.

You don't need to remove the final drive from the bike. Remove the brake caliper and rotor, then remove the final drive cover fasteners. Tap the cover off the final drive. The cover with the bearing, seal, and crownwheel assembly will come off. You will then be able to inspect the inboard end of the crownwheel assembly.

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Thanks for your help CharlieVT...

I have the final drive on the bench. I filled the unit to the edge of the filler hole. With in 20 minutes oil starts to seep from the bottom stud hole....go figure....

You do have the old style FD with the drain plug at the very bottom of the housing? It should look like this only without the tan wiring. If so and you have been filling through the proper hole, check under your front rubber boot and see if it's full of oil. If so, check your transmission level. I suppose the rear tranny seal and the front FD seal could both be leaking, but I defer to Charlie. He is the FD guru.

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Posted too quick....my unit looks similar to the pictures. I will disassemble and report back

There seems to some end play between the aluminum and steel pieces. not very much but detectable. Everything is free and smooth.

No transmission leaks.....

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You can detect play between the aluminum piece which carries the tapered roller bearing and the steel hub which consists of the hub with wheel bolt holes and the crown gear?!?

If so, that's not right. This is the unusual point of failure I referred to above and was described in BMW Owners News. The aluminum piece is an interference fit into the crown gear/hub part. If it is loose, that's a problem. The crownwheel assembly would need to be replaced IMO. And, if it is replaced gear lash between the pinion gear and crown wheel gear needs to be checked and adjusted by reshimming the tapered roller bearing.
Very interesting. I've never seen what you are describing. Only know of it from the BMWON article.

I am guessing that looseness between the aluminum part and crownwheel hub is where your oil is getting into the cavity in the hub.

Very interesting, but troublesome for you.

Let us know what you find....

Not good....you can hold the aluminum part and when you put it on the bench and then pick it up you hear and feel a distinct clunk....

Thanks for all your help....

I can send to you if would want to inspect it...(grin)

Sure, I'd be happy to see it.... but for what purpose other than my own entertainment I don't know.

Here's what I'd do to try and take the pieces apart for inspection:
Remove the bearings. Putting the whole crownwheel assembly in the oven at 250F will ease removal of bearings.
With the bearings off I'd heat the thing again. Also put a damp towel in the freezer.
After the thing gets to temp take it out of the oven, wrap the cold damp towel around the aluminum part and see if you can get the components apart. (You might not even need to cold towel, sometimes things come apart just by heating the whole thing up.)

It would be interesting to inspect the mating surfaces and measure to see what the interference is. I'm not sure what is should be but some of the mech engineers on this site might offer an opinion as to what the fit should be. If you get it apart, and the mating surfaces look okay, you might consider reassembly with a Loktite product specifically designed for that kind of application.

One step ahead of you....tried the heating thing...no good, nothing seems to budge. However, now there is no movement. I'm not sure that is a good thing, because now the two pieces seem locked together. Running out of options....hotter heat....puller....sledge?

On your unit the aluminum and the steel stud hole piece DO move independently of each other...right?

Ok, now you guys have gone and gotten me worried. I've had the rear wheel off twice - the first just after I got the bike (July 09) and had a new rear tire put on it and once in September to repair a flat. Both times I found a very light film of gear lube on the wheel bolts and between the wheel and the hub it bolts to. It has been 10K total miles since July, I've changed the oil in the FD twice - both times clean and no signs of metal in it. No noticeable drop in level, no play in the rear wheel and no visible signs of leakage with the wheel on and torqued down.

I would think you have nothing to worry about.....when I pulled the wheel the oil POURED out....<grin>

No, it is not normal for the aluminum component and the carbon steel hub component of the crown wheel assembly to move with respect to each other. Those parts are fitted together at the BMW factory and the assembly is sold as an individual part. AND, I would expect that the fit between them would be oil tight, but apparently it is not always.

As a matter of fact it seems you can't buy just the crownwheel gear assembly, you have to buy the pinion gear and crown gear as a set. From the MAX BMW parts fische: 33127661910 CROWNGEAR SET: (I=34:13=2,62) - 01/2001 and above 5.61 1 $632.65 OUCH!, I don't think I'd spend 600+ bucks when I could pick up a used drive for a third of that.

You know, if the components of the assembly are stable and have no radial movement, any axial movement would be prevented by the preload. Failures at this location are rare, the only one I ever heard of was the one written up in BMWON. You might be alright just checking the preload and putting it all back together. Just be prepared for oil when you do tire changes!

Yeah, I know... that idea doesn't give a nice warm fuzzy feeling either.

If that were my drive and the only one I had, I'd consider putting it back together as a spare and shop for another used drive to rebuild and use as a primary.

If by chance you do get it apart this may be the thing to use to keep it stable (and sealed) upon reassembly. If not this then some other Loctite product should do the trick. Their website has changed a little bit since I looked the last time, but they make what you need.



http://www.henkelna.com/cps/rde/xchg...UID=0000000M7T

Thanks for the Loctite website....I'm willing to try anything.

As for the two pieces moving separately, the more I got to thinking(scary) the more I could not understand why BMW would make them separate. The two pieces moved so smoothly I thought there was some kind of bearing in there.....

I wonder how much longer that would have gone on.... I'll bet the wheel would have started to "shake ,rattle and "roll" when it failed......yikes!

Thanks to everybody for their wisdom....

Do I understand you to say that the aluminum component spins smoothly in the hub? The aluminum part that the tapered roller bearing is seated on spins freely within the hub that the crownwheel gear is part of?
I didn't understand that from your earlier posts, you did say everything was turning smoothly, but I didn't imagine you were referring to the components of the crown wheel assembly itself. Yikes!

THAT IS the failure mode described in BMWON. Verrly Instersting... Yours is only the second one that I have heard of, the article in BMWON being the first. And I suspect oil leaking out of the wheel bolt holes is an early indication of this failure. I feel silly having first suggested that too much oil would be the cause of oil coming out the bolt holes; I just remember noting that the bolt holes were drilled all the way through the hub during my past assemblies and didn't think about it further; your predicament and findings have helped understand these drives further. WOW!, BMW has sure managed to build a final drive that can fail in so many ways.

With this new understanding, (what I think I know ) I would speculate that any oil leaking out of wheel bolt holes is an indication of impending failure of the crownwheel assembly. I would now say that any oil coming out of the wheel bolt holes is an indication that something is wrong with the crown wheel assembly and should be investigated.

Shit, not another "weep hole" to drill............

Does Loctite really have that much capability that it can replace a shrink fit? I would be inclined to doubt it.

I'm sure aluminum is used as a shaft material in this assembly to keep the axial thermal expansion and hence the axial preload relatively constant as the FD heats up. I'm not familiar with the assembly, but 160 degF temperature shift will cause steel to expand .001 inch/inch, and aluminum .002 inch per inch.

You don't want to heat aluminum to much more than say 300 degF, but at the other end you can use dry ice (-70 degF) or better yet liquid nitrogen (~-350 degF) to assemble or disassemble something. It is a wonder combination of thermal expansion properties between aluminum and steel that allows this. Generally an interference compression fit of about .002 inch per inch is used for a shrink fit.

To salvage the existing assembly, is it possible to shim between the two parts? Aluminum foil is good for ~.0007 per layer? Loctite would be good to give a final seal between the surfaces.

I guess I was not very descriptive my earlier posts. Since I did not have another unit to compare to, and the pieces moved SO smoothly, I thought that was the way of the beast.
I was troubled though, why you would have a bearing on the end AND have one internally.

Anyway, I have disassembled the unit, which was quite easy. Just take a punch, put it in one of the wheel stud holes and tap(somewhat hard, but not real hard) while spinning the aluminum piece. Comes out with no heat or cold.
The unit is very smooth, but not obviously damaged.

I have reassembled the unit using the suggested Loctite.
Glass beaded both pieces(hoping to ruff them up so the Loctite would have something to adhere to) cleaned with solvent and drilled three holes though the steel hub and into the aluminum piece and put in small pins under the big bearing race. Waiting on things to dry before putting the bearing back on.

Was in a big of a hurry (not sure why...) and forgot to take pictures...rats.

You are correct in thinking any oil coming from the crown holes would mean that the two pieces have separated.

I have rode that bike for 10years and know it pretty well. I could tell when that "infamous" bearing everyone was talking about was going bad a couple years ago. Checked the drive oil and found metal flakes that reinforced my "feeling"

With this problem,I had no idea this was going on. My only clue was when I changed the final drive oil, it was really black.
I'm not sure it would cause a catastrophic failure with out some kind of sign. I think more of a problem would be decreased oil in the drive reservoir. The oil would "leak" into the aluminum cavity and there might not be enough to lubricate the ring and pinion good enough (over time...)

Very interesting description of your findings and your repair, thanks.

So the final drive assembly line had some machining problems.
It would seem reasonable to conclude that the interference fit wasn't right. Similar to cases where the tapered roller bearing was loose on its shaft. A problem that I have heard more of than your problem. And since that is the same part that you find loose in the crowngear hub it is sort of more of the same. Bad machining.

Since I suspect many of these drives were set up badly as far as preload calculations, I wonder how much improper preload plays a role in contributing to the kind of failure that you have. Two distinct problems no doubt, but one might compound the other.

In any case, it sounds like you are fashioning a pretty good fix, all things considered. I'd suggest rechecking the preload, you having added Loktite and may have changed things a little bit.

Yeah, sorry we didn't see pics, I am curious of your pin placement. Pins are in blind holes underneath the inner race of the crownwheel bearing?

I have not (fortunately!) had the FD on my 07 apart so I am not real familiar with its design. However, I'm wondering what all can happen when this interference fit fails? Is it just an oil leak issue? I'm assuming that the lug bolts go through both pieces so that there is no danger of the wheel coming off, right?

The pre load between the bearings keeps this assy all together inside the drive housing. The wheel is only bolted to the ring gear. If it does become loose the only indication is oil coming from the bolt holes. The wheel will not fall off.