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Discussion Starter #1
History:
".....repaired twice under warranty at 18,000 miles and again at 23,000. Now at 93,000 it's gone again..... the seal did come out and left an black oil puddle in my garage.( I use the BMW 90 wt oil) I expect I rode 25 miles after hearing the rum rum rum noise."

Here are the forensics at this early stage, I haven't cleaned anything yet, just pulled the FD cover and bearing off the hub. Classic crownwheel bearing failure. Other FD components look okay. Inside of the cover is a little chewed up in spots where the bearing retainer worked at it. I haven't cut open the bearing but the retainer was in advanced stage of destruction; broken in several places and all the rivets pulled out. Heavy pitting of the races visible.

At preliminary inspection tapered roller bearing and pinion and crown gears look okay.

Existing shim was 0.60mm
 

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70,000 miles doesn't seem all that bad. Were you able to measure the correct pre-load required? Were the two previous rebuilds done by the same person/dealer?
Any thoughts about doing a look inside the FD at any pre-determined mileage? If I recall, you looked inside yours at about 30,000 didn't you?

Thanks,
Frank
 

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Discussion Starter #3
fpmlt said:
70,000 miles doesn't seem all that bad. Were you able to measure the correct pre-load required? Were the two previous rebuilds done by the same person/dealer?
Any thoughts about doing a look inside the FD at any pre-determined mileage? If I recall, you looked inside yours at about 30,000 didn't you?

Thanks,
Frank
I understand that the first two rebuilds were done under warranty by the same dealership.
I don't consider 70,000 miles good at all; 150,000-200,000 miles might be acceptable.

I think it makes sense to check the setup of any final drive of the years 99-05 what ever the mileage if you want to have the best piece of mind on long trips. After 06 the number of failures seems to be much smaller, but that's just my "impression" of the reported failures.

I did a check of my drive that I rebuilt at 30K at 70K and it was fine after those 40,000 miles. I might check it again at 100K. I honestly think that these drives when set up properly will go a 100,000 easily no problems. There are plenty of final drives out there that have done just that.
 

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Any idea as to the pre-load being close or correct? How does .6MM shimming compare to what you'd expect to see?
 

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Discussion Starter #5
fpmlt said:
Any idea as to the pre-load being close or correct? How does .6MM shimming compare to what you'd expect to see?
I haven't done my measurements for the new bearing yet.

As previously reported by me here, all the failed FDs I have rebuilt ended up with less preload shimming that what was in there originally.

This one will be interesting because of it's history of two prior rebuilds at a BMW dealership.

I just got back from a ride down to AJ's Cycle to pick up a bearing and seal, so I'll have measurements pretty soon....
 

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fpmlt said:
70,000 miles doesn't seem all that bad. Were you able to measure the correct pre-load required? Were the two previous rebuilds done by the same person/dealer?
Any thoughts about doing a look inside the FD at any pre-determined mileage? If I recall, you looked inside yours at about 30,000 didn't you?

Thanks,
Frank
70,000 miles is absolutely unacceptable for a part like this. I consider 100K an absolute miniumum and really 200K should be the norm. When was the last final drive you had fail on a car? These are well-known mechanical parts that should last nearly forever with normal maintenance and in normal service.
 

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Discussion Starter #7
Voyager said:
70,000 miles is absolutely unacceptable for a part like this. I consider 100K an absolute miniumum and really 200K should be the norm. When was the last final drive you had fail on a car? These are well-known mechanical parts that should last nearly forever with normal maintenance and in normal service.
I agree. I'd like to think that the FD on the KLT would do as well as those on the old Airheads, which for the most part were pretty bullet proof.

When things like auto differentials wear out, output and input bearing shafts get sloppy resulting in weeping oil seals, not catastrophic leaks, and the gears begin the whine.

It would be nice to think that the BMW KLT final drive would run until it just sort of wears out, rather than a sudden failure like we see. I tend to think that a properly assembled and maintained one will do just that. Remember what we are seeing here is the small percentage of the drives that have failed, not the much larger percentage that are running just fine.

(FD cover is in the oven) ;)
 

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Curtis,

I'm guessing you'll use something more than 0.60 during reassembly if being too tight is the culprit.

Bob, the BMW mechanic, didn't share with me the shims used the 2 times he rebuilt it. Nor did he say what was in there as an original. Guess it MIGHT be in his shop records. I just don't know. :(

Sounds like it's OK to rebuild it...................let me know when you need funds. Curtis, I really appreciate your help.

Thanks for the pics,

Vern :bmw:
 

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Discussion Starter #9
Here's my data on this drive:

From Dman's dial indicator method, shim range: 0.30-0.35mm
From the BMW Service Manual depth micrometer method, shim range: 0.25-0.30mm

I'll shim with 0.30mm shim.

Assuming the failed bearing and the replacement bearing were dimensionally the same, the original shim was 0.30mm too thick.

Since this drive had failed twice before and went 70K miles on the last rebuild, I double checked measurements using both methods. Within a little measurement error the results are essentially consistent. I usually discard a couple of measurements that are at large variance from the majority of measurements. If I were to use those most extreme measurements the thickest shim I could come up with is 0.40mm, which is still significantly less than the 0.60mm shim that was in there.

Yeah, I'd like to have been a fly on the wall during the previous rebuilds. Did they assume that it was a matter of bad bearings and just replace 'em without remeasuring for preload? We'll never know, 'cause if they didn't do the measurements they aren't going to tell us.

Thanks for the opportunity to evaluate this drive.

Excel spreadsheet showing calculations attached:
 

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For what it's worth Curtis the last one I rebuilt it had .014 preload from the factory. It went a little over 100,000 miles. I went from a .7mm shim to a .4mm shim with the new bearing. His bearing definitely had more side load wear marks than my bearing did. My bearing had the proper preload from the factory.
 

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CharlieVT said:
I agree. I'd like to think that the FD on the KLT would do as well as those on the old Airheads, which for the most part were pretty bullet proof.

When things like auto differentials wear out, output and input bearing shafts get sloppy resulting in weeping oil seals, not catastrophic leaks, and the gears begin the whine.

It would be nice to think that the BMW KLT final drive would run until it just sort of wears out, rather than a sudden failure like we see. I tend to think that a properly assembled and maintained one will do just that. Remember what we are seeing here is the small percentage of the drives that have failed, not the much larger percentage that are running just fine.

(FD cover is in the oven) ;)
I agree, Charlie. Then again, if auto units failed at the same percentage as LT drives fail, were would have thousands if not hundreds of thousands of car differentials fail each year... :)

Just trying to keep it in perspective. :)
 

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CharlieVT said:
I agree. I'd like to think that the FD on the KLT would do as well as those on the old Airheads, which for the most part were pretty bullet proof.

When things like auto differentials wear out, output and input bearing shafts get sloppy resulting in weeping oil seals, not catastrophic leaks, and the gears begin the whine.

It would be nice to think that the BMW KLT final drive would run until it just sort of wears out, rather than a sudden failure like we see. I tend to think that a properly assembled and maintained one will do just that. Remember what we are seeing here is the small percentage of the drives that have failed, not the much larger percentage that are running just fine.

(FD cover is in the oven) ;)
Curtis,
My first drive went at 127K, currently have 97K on Steve R's Red Rover (11k+86K for me)Final drive. I guess I'm just lucky.
 

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No argument here guys, I'm just trying to learn/understand. Reason I thought that 70 seemed OK, I guess, was that it's lots longer than most go before failure. Where I "think" this is different from any car, is that it's a single load bearing (no pun intended) point, and I just can't imagine the forces placed on it, considering how hard some of us ride these things, and how heavy they are.
Like I said, just trying to understand, and appreciate all the different perspectives.
Frank.
 

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Discussion Starter #14
fpmlt said:
No argument here guys, I'm just trying to learn/understand. Reason I thought that 70 seemed OK, I guess, was that it's lots longer than most go before failure. Where I "think" this is different from any car, is that it's a single load bearing (no pun intended) point, and I just can't imagine the forces placed on it, considering how hard some of us ride these things, and how heavy they are.
Like I said, just trying to understand, and appreciate all the different perspectives.
Frank.
I imagine that folks who lost their FD at 18K miles would have been happier with 70K. :histerica

I agree that the stresses on this FD have to be much greater than the standard auto differential, or even the FD of an old Airhead with a double swingarm and a full axle.

Anyone have any idea how many K1200LTs BMW has sold since the model was introduced?
 

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CharlieVT said:
I imagine that folks who lost their FD at 18K miles would have been happier with 70K. :histerica

I agree that the stresses on this FD have to be much greater than the standard auto differential, or even the FD of an old Airhead with a double swingarm and a full axle.

Anyone have any idea how many K1200LTs BMW has sold since the model was introduced?
I don't know if the stresses are higher or not, but if they are that was a design decision by BMW. Look at the hub on a front-wheel drive car. It is the same basic "use case" as for the LT. It is single-sided and carries more weight in all but the smallest of cars than does the LT. A fully loaded LT may have 700 lbs on the rear wheel. Most FWD cars weigh at least 3,400 lbs and typically have 60% of their weight on the front axle. That amounts to 1,000 lbs on each front hub. Most of these hubs have two bearings also and a large cantilever as the center of the tire contact patch is well outside of the bearings, much as with the LT.

I personally don't see any real difference in the basic design or loading. If anything, the auto system is more severely loaded as it must handle both vertical forces and substantional lateral forces during corning. The lateral forces add to the torque on the hub in addition to the torque caused by the offset in the vertical force. The motorcycle has to counteract only the vertical force and the torque from the offset in the vertical force, but no significant lateral force.

I think the motorcycle configuration if anything should be a far easier design from a bearing perspective.
 

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Discussion Starter #16
I think you make a very good point. Consider the front wheels of an all wheel drive/4 wheel drive vehicle. There is a drive shaft input, steering capability, and a lot of weight.

It makes me think the BMW FD design is more than adequate, IF properly set up. I've said before that you can fault the design engineers for not making the FD really easy to set up properly, but probably the design is robust enough when it is properly set up.


Voyager said:
I don't know if the stresses are higher or not, but if they are that was a design decision by BMW. Look at the hub on a front-wheel drive car. It is the same basic "use case" as for the LT. It is single-sided and carries more weight in all but the smallest of cars than does the LT. A fully loaded LT may have 700 lbs on the rear wheel. Most FWD cars weigh at least 3,400 lbs and typically have 60% of their weight on the front axle. That amounts to 1,000 lbs on each front hub. Most of these hubs have two bearings also and a large cantilever as the center of the tire contact patch is well outside of the bearings, much as with the LT.

I personally don't see any real difference in the basic design or loading. If anything, the auto system is more severely loaded as it must handle both vertical forces and substantional lateral forces during corning. The lateral forces add to the torque on the hub in addition to the torque caused by the offset in the vertical force. The motorcycle has to counteract only the vertical force and the torque from the offset in the vertical force, but no significant lateral force.

I think the motorcycle configuration if anything should be a far easier design from a bearing perspective.
 

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CharlieVT said:
I think you make a very good point. Consider the front wheels of an all wheel drive/4 wheel drive vehicle. There is a drive shaft input, steering capability, and a lot of weight.

It makes me think the BMW FD design is more than adequate, IF properly set up. I've said before that you can fault the design engineers for not making the FD really easy to set up properly, but probably the design is robust enough when it is properly set up.
This is my suspicion also. If the design defect involved the bearing(s) being too small for the loads applied, then the failure rate would be closer to 100% than 4%. Since the failure rate appears to be much less than 100%, I suspect that the design defect is, as you suggest, the fact that the FD setup procedure is simply too complicated for a typical production line.
 

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CharlieVT said:
Anyone have any idea how many K1200LTs BMW has sold since the model was introduced?
Didn't someone report the number a couple monthgs ago? I believe it was 13,000 and change worldwide.

Loren
 

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Discussion Starter #19
wa1200lt said:
Didn't someone report the number a couple monthgs ago? I believe it was 13,000 and change worldwide.

Loren
Thanks for the reply. I must have missed the previous post.
 

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I was wondering... that happens when I aint out riding...

Has anyone compared the number of "FD" failures to those running the "recommended" tire air pressures?

Could the increased air pressure be 'jarring' the FD / sending undamped vibrations into the FD setting up failure?

Man, I just need to go ride... =)
 
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