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post #1 of 47 Old Oct 17th, 2006, 10:00 pm Thread Starter
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Unhappy 17 Ball Final Drive Toast

Servicing the bike this afternoon and pulled final drive drain plug and I now have enough metal flake to paint an 18 wheeler. No Noise, no wobble, no indication of a bearing failure at all until I pulled the drain plug. I had the 17 ball bearing installed at 28,000 miles and it is now at 69,500 miles. I have been running Mobile 1 75/140 full syn gear lub. and have been changing it at 6,000 mile intervals. I will start pulling it apart tomorrow morning, Oh joy.
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post #2 of 47 Old Oct 18th, 2006, 3:19 am
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Bummer. Be sure and take some pics to share.

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post #3 of 47 Old Oct 18th, 2006, 9:33 am
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Quote:
Originally Posted by Moonshine
Servicing the bike this afternoon and pulled final drive drain plug and I now have enough metal flake to paint an 18 wheeler. No Noise, no wobble, no indication of a bearing failure at all until I pulled the drain plug. I had the 17 ball bearing installed at 28,000 miles and it is now at 69,500 miles. I have been running Mobile 1 75/140 full syn gear lub. and have been changing it at 6,000 mile intervals. I will start pulling it apart tomorrow morning, Oh joy.
Do you know if they checked the bearing clearance and shimmed it properly when they put in the new bearing? I do not subscribe to the "just replace the bearing and seal" camp at all. Axial clearances in bearings have several times the tolerance range of Radial clearances, and should be checked for the correct shim thickness needed to get the correct preload.

I have always felt that a final drive "rebuild" stood a good chance of failing again, and doubt that over 10% of dealers have a clue how to do it properly.

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David Shealey
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post #4 of 47 Old Oct 18th, 2006, 9:57 am
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Quote:
Originally Posted by dshealey
Do you know if they checked the bearing clearance and shimmed it properly when they put in the new bearing? I do not subscribe to the "just replace the bearing and seal" camp at all. Axial clearances in bearings have several times the tolerance range of Radial clearances, and should be checked for the correct shim thickness needed to get the correct preload.

I have always felt that a final drive "rebuild" stood a good chance of failing again, and doubt that over 10% of dealers have a clue how to do it properly.
OMG we agree again

<grin>

actually this is a good post, I loved to hear folks say they replaced this or that , then ask them what the clearences were, get a puzzled look from them about 70% of the time


i'm interested in seeing the new drive failure rate on the GS Gt S series bikes, (Why I have no idea since we already bought them)

Tom

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post #5 of 47 Old Oct 18th, 2006, 11:25 am
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Have you seen this?

FIRE

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post #6 of 47 Old Oct 18th, 2006, 12:06 pm Thread Starter
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Question 17 Ball Final Drive Toast

I doubt if the assembly was checked for proper preload however I don't know for sure, since they did not remove the final drive from the bike to replace the bearing. However I am going to do this one myself and I will check for proper bearing preload and I will do it cold (room temp) and at a higher temp (let it soak at approx 150 degrees) this should allow for the expansion of the ring gear carrier and bearings (steel parts) and the aluminum housing to become temp stable then I will check again for preload. This was the method we used when we assembled the sprint car quick change rear ends that were using a steel axle assembly. The center sections were either aluminum or magnesium and there was a significant difference between cold & hot clearances or as we called it side play or bearing preload. I think that I will continue to replace the bearing at 30,000 to 40,00 mile intervals though just as a preventive measure.

For the record, when I look at the old 19 ball bearing the dealer removed I see that the spalling that had begun to show is centered in the ball grove of the outer race. I would think that if the preload was to tight the spalling would start more to the side of the outer race bearing groove.

All suggestions and additional information is welcome.

(New information) the bearing & seal are out of stock at Chicago BMW & it will be two weeks or more before I get the replacement bearing & seals.
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post #7 of 47 Old Oct 18th, 2006, 1:09 pm
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Quote:
Originally Posted by Moonshine
(New information) the bearing & seal are out of stock at Chicago BMW & it will be two weeks or more before I get the replacement bearing & seals.
In my experience with Chicago BMW parts ordering, just about everything is out of stock. They offer 20% off BMW list prices, but I think they keep their inverntory low. I order from them, but not when I am in a hurry because I anticipate they will be ordering the part from BMW for me.
I would not interpret the fact the Chicago is NIS on any item as meaning there are spot shortages of the part.
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post #8 of 47 Old Oct 18th, 2006, 3:32 pm
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post #9 of 47 Old Oct 18th, 2006, 8:56 pm
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Quote:
Originally Posted by clay
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FIRE

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yes but too many questions are unanswered, like why? what was the diagnoses?

was it brake related like another final drive "fire" we know tha tone personally here, the brake was dragging and got so hot it caught the rubber boot on fire

Tom

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post #10 of 47 Old Oct 18th, 2006, 8:59 pm
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Quote:
Originally Posted by CharlieVT
In my experience with Chicago BMW parts ordering, just about everything is out of stock. They offer 20% off BMW list prices, but I think they keep their inverntory low. I order from them, but not when I am in a hurry because I anticipate they will be ordering the part from BMW for me.
I would not interpret the fact the Chicago is NIS on any item as meaning there are spot shortages of the part.
I don't really think any BMW dealer stocks anything more than common maintenance parts.. and just a few weeks supply at that.

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post #11 of 47 Old Oct 18th, 2006, 9:48 pm
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Axial Clearance of rear drive bearing.

Quote:
Originally Posted by dshealey
Do you know if they checked the bearing clearance and shimmed it properly when they put in the new bearing? I do not subscribe to the "just replace the bearing and seal" camp at all. Axial clearances in bearings have several times the tolerance range of Radial clearances, and should be checked for the correct shim thickness needed to get the correct preload.

I have always felt that a final drive "rebuild" stood a good chance of failing again, and doubt that over 10% of dealers have a clue how to do it properly.
David, because you noted (in a previous post) that the axial clearance tolerance of these bearings could vary .005 plus, I did a feeler stock comparison check comparing the old 19 ball FAG with the new 17 ball SKF.
With only one thousandth difference, I rebuilt it with the same .028 thick shim. The FAG-19 was .006; and the SKF-17 was .005

Barnett
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post #12 of 47 Old Oct 18th, 2006, 10:16 pm
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I discussed this situation in detail today riding for several hours (in a cage) with my very retired mech engineer brother. He asked if the ball bearing is a radial or an angular contact affair. I had assumed earlier it is simply a radial bearing. He strongly felt that an angular contact bearing might be appropriate when opposed by a tapered roller bearing, but that a radial bearing would not.

He also agreed that replacement bearings are not necessarily the same dimension and that a .002 inch thrust shim increment sounded pretty coars to him.

I have not seen a cross section drawing of this application - just what I read here. Does anyone have a sketch?

Q - Is the orientation of the ball bearing very specific (i. e. angular contact)? or can it be installed either way (suggesting a radial ball bearing)
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post #13 of 47 Old Oct 19th, 2006, 12:01 am
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Post moved to correct thread.

All better, guys?

Ken
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Last edited by meese; Oct 19th, 2006 at 3:45 am.
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post #14 of 47 Old Oct 19th, 2006, 1:04 am
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Red face

Quote:
Originally Posted by meese
I had them add the BC-2 to my '99 for free as part of the purchase. When that failed (constant static), BMW told them to pull it and refund my money. There was no ComSystem (BC-3) yet, so they wrote me a check.
Huh? Ken, me thinks you have mixed up your threads!

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post #15 of 47 Old Oct 19th, 2006, 1:15 am
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Originally Posted by AlaskaFish
Huh? Ken, me thinks you have mixed up your threads!

John
Thanks John,

I went all the way back through the thread looking for a BC something , or other related to the drivetrain.
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post #16 of 47 Old Oct 19th, 2006, 7:46 am
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Quote:
Originally Posted by niel_petersen
I discussed this situation in detail today riding for several hours (in a cage) with my very retired mech engineer brother. He asked if the ball bearing is a radial or an angular contact affair. I had assumed earlier it is simply a radial bearing. He strongly felt that an angular contact bearing might be appropriate when opposed by a tapered roller bearing, but that a radial bearing would not.

He also agreed that replacement bearings are not necessarily the same dimension and that a .002 inch thrust shim increment sounded pretty coars to him.

I have not seen a cross section drawing of this application - just what I read here. Does anyone have a sketch?

Q - Is the orientation of the ball bearing very specific (i. e. angular contact)? or can it be installed either way (suggesting a radial ball bearing)
It is a strictly radial bearing, not angular contact. The little tapered roller on the other end of the axle is only to keep the shaft in line with and take some of the load from the pinion bearing. It is way too small to act as opposition force for an angular contact bearing. It does take some axial force, but the ball bearing is the major radial axle support in this case.

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Last edited by dshealey; Oct 19th, 2006 at 12:43 pm.
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post #17 of 47 Old Oct 19th, 2006, 8:40 am
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Quote:
Originally Posted by niel_petersen
I discussed this situation in detail today riding for several hours (in a cage) with my very retired mech engineer brother. He asked if the ball bearing is a radial or an angular contact affair. I had assumed earlier it is simply a radial bearing. He strongly felt that an angular contact bearing might be appropriate when opposed by a tapered roller bearing, but that a radial bearing would not.

He also agreed that replacement bearings are not necessarily the same dimension and that a .002 inch thrust shim increment sounded pretty coars to him.

I have not seen a cross section drawing of this application - just what I read here. Does anyone have a sketch?

Q - Is the orientation of the ball bearing very specific (i. e. angular contact)? or can it be installed either way (suggesting a radial ball bearing)
there was one floating around not long ago, i thoughtI kept it, there is also one floating around of the new rear drive well showing a slightly tapered bearing, , I'd really like to see the parts myself, so I could give informed opinion of this newer design. It is a weight issue on our LT, as ourfinals fail much more often than any other bmw's, it needs more support IMHO.

but face it, the lt isnot the biggest seller, a couple years ago (maybe not that long ago) when I did some checking to see how my K12Lt bikes had been made, it was right at 5000 for all years to that point, if a 3% or 4% failure is correct, well then it would be a waste of money for BMW to do a complte redesign for our LT's, I bet though it is more like 10% or more failure rate

I'm hoping the new ones do not fail on the GS or GT models, My K12LT is history, this is my last one, I Loved it but I have no need for a big bike like this anymore when they have somehting very comparable out set up the GT right for TWO up and we have what everyone wants 100 lbs or more lighter, more power, not top heavy.

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post #18 of 47 Old Oct 19th, 2006, 9:49 am
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Quote:
Originally Posted by tmgs
--------------but face it, the lt isnot the biggest seller, a couple years ago (maybe not that long ago) when I did some checking to see how my K12Lt bikes had been made, it was right at 5000 for all years to that point,-------------
There are a lot more than that. The BMWNA rep at CCCR Santa Fe in 2002 stated that there were over 7,000 LTs sold just in the US at that time. He gave the exact number, think it was about 7,200

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post #19 of 47 Old Oct 19th, 2006, 9:53 am
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http://www.thk.se/pdf/382-E.pdf

This is what I would like to put in a final drive to test. The RB816 crossed roller bearing is 80X120X16 mm, where the standard ball is 85X120X18 mm. It would require grinding the 85MM shaft to 80MM, and using a 2MM spacer on the outer race. If I still had the LT, and the failed drive I had in the garage for awhile, I would be very tempted to try it.
The standard ball bearings have a roughly 5500 pound radial rating, this crossed roller bearing has a 6900 pound rating.

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post #20 of 47 Old Oct 19th, 2006, 11:58 am
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Hi David,

I like that bearing design better than what we currently have. I believe the number is actually RB8016.

I haven't had a drive apart yet (knock on wood) so I'm not that familiar with the drive design. You mention needing a 2mm spacer on the outer race but I'm wondering if 1mm spacers on each side would be better/worse or the same. What would you suggest?

I'm also a little confused by the greasing hole terminology in the brochure. Would we need to do something different or is the current drive design OK. Does the standard bearing have seals? It looks like these are available with one or two seals....would we need to remove any seals?

Maybe we could convince Don Arthur to get another LT and start riding again. If we put one of these on his bike we would get some answers pretty quick

With a rather low failure rate we would need to get these in quite a few bikes to determine if they were any better. If they ended up not working out it would be a problem since the shaft would be turned down already.

hmmm....what to do?


Kevin

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post #21 of 47 Old Oct 19th, 2006, 12:36 pm Thread Starter
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Bearing type

I am not sure that this type of bearing would be applicable to the final drive. It appears to be designed for applications of CNC machinery rotary placement where extreme accuracy is required. It does not appear as though this would be a press fit application as the current bearing is and I don't know but it may also be for a relative low RPM application. Its just too bad that they did not design this using a tapered roller bearing in lew of the ball. However I did notice that on some of the new cars they are now using a sealed for life ball bearing assemblies for the front wheels, it suprised me. The ball bearing lobby is hard at work.
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post #22 of 47 Old Oct 19th, 2006, 12:41 pm
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Quote:
Originally Posted by kevincook
Hi David,

I like that bearing design better than what we currently have. I believe the number is actually RB8016.
Yep, just typed too fast.
Quote:

I haven't had a drive apart yet (knock on wood) so I'm not that familiar with the drive design. You mention needing a 2mm spacer on the outer race but I'm wondering if 1mm spacers on each side would be better/worse or the same. What would you suggest?
The gear face the bearing inner race is pressed against has to remain in the same position at assembly, so a 2mm spacer would have to be used on the hub side of the outer race to maintain that.
Quote:

I'm also a little confused by the greasing hole terminology in the brochure. Would we need to do something different or is the current drive design OK. Does the standard bearing have seals? It looks like these are available with one or two seals....would we need to remove any seals?
That is used where lubrication has to be occasionally re-introduced. In the final drive, the lubrication is always there.
Quote:

Maybe we could convince Don Arthur to get another LT and start riding again. If we put one of these on his bike we would get some answers pretty quick
Don has a GT on order, getting it in January.
Quote:

With a rather low failure rate we would need to get these in quite a few bikes to determine if they were any better. If they ended up not working out it would be a problem since the shaft would be turned down already.
Yep. I would try it for myself, but would not expect to do more than the one. It would be very difficult to get any real data, but I would be trying to see if there were any relatively early issues with the setup.
Quote:

hmmm....what to do?


Kevin
I just threw this out for provoking thought regarding bearing arrangements. Probably not too many people here other than myself that would do the work to try it.

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David Shealey
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post #23 of 47 Old Oct 19th, 2006, 12:59 pm
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I was curious so I called our bearing supplier to get a quote.

$441.55

Ouch!

It would probably make more sense just to buy a new drive from BMW and hope they have actually solved this problem with improved manufacturing procedures. I still like the idea though.

Kevin

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post #24 of 47 Old Oct 19th, 2006, 2:29 pm
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The crossed roller units are OK & I have used them for quasi-static industrial applications, but note that there is no published speed rating. Did you find that some place else? Otherwise it is the sort of bearing only appropriate for very slow applications like telescope mountings etc.

This application with an 85 (or 80?) mm bore and a continuous operating speed of say 1200 RPM isn't trivial. I suspect the life problem isn't just radial load carrying capacity, it is also speed limited. Frankly most of my career's bearing failures have been speed related.

Angular contact bearings handle speed very well, but they must be thrust loaded by either using them in pairs or by something else to get the precision spindle axes needed to maintain the gear alignments enough to minimize noise.

Tapered roller bearings can handle thrust well but don't like the combination of speed and large IDs. Getting the thrust preload with a tapered roller bearing (what is the present size?) would seem an unusual but reasonable design approach. Might someone make such an angular contact bearing in that large ball bearing size? Gotta go look...........

BTW - Oil will improves a bearing's speed capability - especially compared to grease (or sealed grease). But the gears will require the oil to be heavy (and full of anti-wear additives) to survive. Magnetic drain plugs would be necessary to keep the tramp metal from the gears from destroying the bearing races.
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post #25 of 47 Old Oct 19th, 2006, 6:34 pm
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Exclamation Caution

Quote:
Originally Posted by wilbar00c
David, because you noted (in a previous post) that the axial clearance tolerance of these bearings could vary .005 plus, I did a feeler stock comparison check comparing the old 19 ball FAG with the new 17 ball SKF.
With only one thousandth difference, I rebuilt it with the same .028 thick shim. The FAG-19 was .006; and the SKF-17 was .005

Barnett
That may be OK only if the FD was properly set up at the onset.

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post #26 of 47 Old Oct 19th, 2006, 9:27 pm
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Quote:
Originally Posted by murray
That may be OK only if the FD was properly set up at the onset.
Pete, I feel I lucked out with a good factory set-up. I trust the stronger 17 ball retainer. So far so good, with 4K on the SKF17.

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post #27 of 47 Old Oct 20th, 2006, 10:14 am
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Quote:
Originally Posted by niel_petersen
The crossed roller units are OK & I have used them for quasi-static industrial applications, but note that there is no published speed rating. Did you find that some place else? Otherwise it is the sort of bearing only appropriate for very slow applications like telescope mountings etc.
I used several of these in large servo driven presses, using ball screws. The crossed roller bearing supported the ball nuts, which were spun by the large servo motor through a large timing belt drive, and the screws were non-rotating, and pushed down the platen of the press. These were run at about 1600 RPM on up/down travel, but were slowed down considerably when the load was being applied. I actually have one of them at home, and I think it is the size we are talking about, or close. It is a sealed "UU" unit. You are correct, the catalog does not list any speed limitations. But, the rollers are seperated by non metallic seperators, so any speed limitation would likely be quite high.
Quote:
This application with an 85 (or 80?) mm bore and a continuous operating speed of say 1200 RPM isn't trivial. I suspect the life problem isn't just radial load carrying capacity, it is also speed limited. Frankly most of my career's bearing failures have been speed related.
We probably work in different engineering areas. Just about every bearing failure I have been involved in was either incorrect design use, misallignment, and most of all, incorrect installation practices.
Quote:

Angular contact bearings handle speed very well, but they must be thrust loaded by either using them in pairs or by something else to get the precision spindle axes needed to maintain the gear alignments enough to minimize noise.

Tapered roller bearings can handle thrust well but don't like the combination of speed and large IDs. Getting the thrust preload with a tapered roller bearing (what is the present size?) would seem an unusual but reasonable design approach. Might someone make such an angular contact bearing in that large ball bearing size? Gotta go look...........
The opposing bearing on the crown gear is a 25x52x16.25 tapered roller.

I think one problem is that the final drive housing is die cast aluminum, and not all that thick walled. When it heats up, the 0.001-0.002" preload probably disappears, even likely becoming clearance.
Quote:

BTW - Oil will improves a bearing's speed capability - especially compared to grease (or sealed grease). But the gears will require the oil to be heavy (and full of anti-wear additives) to survive. Magnetic drain plugs would be necessary to keep the tramp metal from the gears from destroying the bearing races.
These final drive units seem to be quite good at generating tramp metal! The drain plug almost always has fine metal on it, and even with the magnetic drain plug, there is also usually a metallic sheen to the oil when looked at in sunlight.

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post #28 of 47 Old Oct 20th, 2006, 2:36 pm
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>These final drive units seem to be quite good at generating tramp metal! <

Verrrrry interesting!

Q - Does the outer race of the crown bearing roll - or does it stand still? If it rotates, the outer race groove could accumulate debris, initiating failure.
How about the tapered roller bearing?

Q - Is virtually all the wheel radial load taken by the ball bearing?

Q - What are the average diameters of the gear set?

Q - Assuming the aluminum housing and the steel shaft are running the same temperature, does the increased housing expansion with temperature cause the preload to increase - or decrease?

Q - What is the approx center-to-center spacing between the bearing roller/ball systems (i. e. not inside to inside)?
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post #29 of 47 Old Oct 20th, 2006, 2:58 pm
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Quote:
Originally Posted by niel_petersen
>These final drive units seem to be quite good at generating tramp metal! <

Verrrrry interesting!

Q - Does the outer race of the crown bearing roll - or does it stand still? If it rotates, the outer race groove could accumulate debris, initiating failure.
How about the tapered roller bearing?
The outer race is stationary, clamped between the housing and cover. The tapered roller has it's outer race pressed into the housing, the inner race pressed onto the crown gear shaft.
Quote:

Q - Is virtually all the wheel radial load taken by the ball bearing?
Yes
Quote:

Q - What are the average diameters of the gear set?
I don't have my old unit any longer, so I cannot measure. The crown gear is probably about 1-1/2 to 2" smaller in diameter than the outside of the housing.
Quote:

Q - Assuming the aluminum housing and the steel shaft are running the same temperature, does the increased housing expansion with temperature cause the preload to increase - or decrease?
Preload would decrease as the housing heats up.
Quote:

Q - What is the approx center-to-center spacing between the bearing roller/ball systems (i. e. not inside to inside)?
Again, wish I still had my old drive to check, but guessing about 3".

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post #30 of 47 Old Oct 21st, 2006, 6:12 am
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Quote:
Originally Posted by wilbar00c
Pete, I feel I lucked out with a good factory set-up. I trust the stronger 17 ball retainer. So far so good, with 4K on the SKF17.
Barn, Wishing you tons of trouble free miles!

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post #31 of 47 Old Oct 21st, 2006, 1:31 pm
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Has anyone got a good closeup picture of the inner race of a failed crown bearing? or even one that has been removed from service as a precaution? This would assume that the bearing has been disassembled by removing the cage.
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post #32 of 47 Old Oct 21st, 2006, 3:00 pm
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Quote:
Originally Posted by niel_petersen
Has anyone got a good closeup picture of the inner race of a failed crown bearing? or even one that has been removed from service as a precaution? This would assume that the bearing has been disassembled by removing the cage.
Here is the thread that I had regarding evaluation of two bearings by an SKF bearing engineer. Mine had failed catastrophically, Dick's had only started to fail.

http://www.bmwlt.net/ubbthreads/show...&Number=114601

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post #33 of 47 Old Oct 21st, 2006, 4:22 pm
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Dave - Thanks for the info(s). Earlier I had not found your analysis from the SKF engineer. I agree you are right - that it is a combination of ham-handed assembly techniques and possibly excessive operational preload. I'm surprised though that the lesser failed bearing couldn't give more information to SKF. Possibly the first bearing was brinneled on assembly and the second bearing was maybe not brinneled, but failed for excessive preload reasons? It is hard, but not impossible, to imagine that the BMW factory would press on the outer race.

The FD assembly (I found some pictures elsewhere) looks like it is blind - in that there is no way to determine the amount of the preload dimension once the clearance is taken up.

What does the BMW manual say? How is preload established?

I agree - magnetic drain plugs and frequent oil changes are the stopgap fix. Another possibility is to use a 7917 angular contact bearing but I'm not yet sure that would be any better. Getting it off the shaft would scrap the bearing if there are no puller relief slots.
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post #34 of 47 Old Oct 21st, 2006, 6:19 pm Thread Starter
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Lightbulb Final Drive set up

In my case preload will be determined by very careful measurements using a granite surface plate, precision parallels, depth mike, micrometers, and dial indicators and a lot of time (which I have more of than money). After assembly and heating to 150 degrees I will be able to determine if the preload diminishes and becomes clearance. BMW does have a final drive set up fixture but I would bet that very few BMW shops have one of these.

Yes Niel I have the 19 ball bearing that was removed from my final drive at 28,000 miles. I fact I carried it with me as a spare if I was ever caught out in the boon docks and had a final drive failure. Under close inspection it was starting to show the beginning of spalling in the center of the outer race groove and at the same spacing as the center to center of the ball spacing. That bearing was destined to fail IMHO mabe it would have lasted another 5, 10 or 15 thousand miles I will never know. To the naked eye with some lubrication still on it the bearing appeared to be OK but by inspecting it with a glass you can see the spalling areas.
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post #35 of 47 Old Oct 21st, 2006, 9:30 pm
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Quote:
Originally Posted by niel_petersen
Dave - Thanks for the info(s). Earlier I had not found your analysis from the SKF engineer. I agree you are right - that it is a combination of ham-handed assembly techniques and possibly excessive operational preload. I'm surprised though that the lesser failed bearing couldn't give more information to SKF. Possibly the first bearing was brinneled on assembly and the second bearing was maybe not brinneled, but failed for excessive preload reasons? It is hard, but not impossible, to imagine that the BMW factory would press on the outer race.

The FD assembly (I found some pictures elsewhere) looks like it is blind - in that there is no way to determine the amount of the preload dimension once the clearance is taken up.

What does the BMW manual say? How is preload established?
The pre-load is set by taking measurements of the bearing bore in the housing cover, then with a special alignment tool to hold the bearing in alignment, another measurement is taken of the bearing outer-race height above the housing, then that is subtracted from the cover depth, and shims selected to be 0.002-0.004" more than the bearing measurement to assure that much pre-load when the housing cover is bolted on.
Quote:

I agree - magnetic drain plugs and frequent oil changes are the stopgap fix. Another possibility is to use a 7917 angular contact bearing but I'm not yet sure that would be any better. Getting it off the shaft would scrap the bearing if there are no puller relief slots.
I don't believe an angular contact bearing would survive long, as there would be resistance to any wheel twisting load on only one point in the bearing, with no resistance on the other side 180 degrees around after the bearing clearance was overcome.

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post #36 of 47 Old Oct 21st, 2006, 11:47 pm
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Moonshine and DSHealey etc - Wouldn't there be brinell marks on the groove edges rather than the bottom if the bearing is assembled by pressing on the wrong race? I just thought of that.

The SKF analysis suggested the inner race of the crown bearing was fretting in its shaft, but it didn't appear from the photo to be very much if at all to me. Sustained operation in a failed mode could have aggravated the fretting.

I'm surprised at the small oil volume in this gearset. Might the oil turbulence be so great that magnets can't hold the tramp metal?

The preload setup procedure sounds really futtzy (sp?) difficult in the field, and prone to errors. Are the shims removeable on disassembly without pressing off bearings? Might a shim cut as a gearcase gasket be temporarily used on a preassembly check to more directly measure the clearance (or lack thereof) with a dial indicator? This shim would be removed on final assembly.

I was thinking the angular contact bearing would be preloaded by the tapered roller bearing. Thrust loads shouldn't be that great & would originate mostly from the pressure angle of the gearset.
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post #37 of 47 Old Oct 22nd, 2006, 10:18 am
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Quote:
Originally Posted by niel_petersen
Moonshine and DSHealey etc - Wouldn't there be brinell marks on the groove edges rather than the bottom if the bearing is assembled by pressing on the wrong race? I just thought of that.

The SKF analysis suggested the inner race of the crown bearing was fretting in its shaft, but it didn't appear from the photo to be very much if at all to me. Sustained operation in a failed mode could have aggravated the fretting.

I'm surprised at the small oil volume in this gearset. Might the oil turbulence be so great that magnets can't hold the tramp metal?

The preload setup procedure sounds really futtzy (sp?) difficult in the field, and prone to errors. Are the shims removeable on disassembly without pressing off bearings? Might a shim cut as a gearcase gasket be temporarily used on a preassembly check to more directly measure the clearance (or lack thereof) with a dial indicator? This shim would be removed on final assembly.

I was thinking the angular contact bearing would be preloaded by the tapered roller bearing. Thrust loads shouldn't be that great & would originate mostly from the pressure angle of the gearset.
Mine did have spalled spots on ball pitch in the sides of the inner race, and the SKF engineer mentioned that, saying that was likely from impact, probably at assembly.

I did not think the fretting was an issue, as I had the bearing and shaft in my hands, and the fretting was there, but minimal. The bearing had a pretty good press fit.

There is no way to check pre-load with the housing cover in place. I had thought that if the housing cover would slip over the bearing easily enough one could put in an extra shim, push the cover down until everything was settled in place, then measure the gap between housing and cover. Then you could put in a shim 0.002-0.004" thicker than the extra one used for testing.

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post #38 of 47 Old Oct 22nd, 2006, 11:16 am Thread Starter
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Lightbulb Test for bearing clearance at assembly?

Dshealey what are you thoughts about this??

If a person would assemble the final drive and leave out the bearing shim and seal, and in place of the bearing spacer shim install some plasta-gauge material at 90 degree spacing to get a reading of the clearance between the bearing & the case to determining the thickness of bearing spacer required. By tighting the cover bolts to the proper torque it should flatten the plasta-gauge to get a thickness reading and the cover should hold the bearing square with the center line of the shaft to get equal force on the plasta-gauge strips. The cover will have to be heated to alow the bearing to slide in the cover to crush the plasta-gauge while torquing the bolts.

Remember be kind.
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post #39 of 47 Old Oct 22nd, 2006, 12:19 pm
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Quote:
Originally Posted by Moonshine
Dshealey what are you thoughts about this??

If a person would assemble the final drive and leave out the bearing shim and seal, and in place of the bearing spacer shim install some plasta-gauge material at 90 degree spacing to get a reading of the clearance between the bearing & the case to determining the thickness of bearing spacer required. By tighting the cover bolts to the proper torque it should flatten the plasta-gauge to get a thickness reading and the cover should hold the bearing square with the center line of the shaft to get equal force on the plasta-gauge strips. The cover will have to be heated to alow the bearing to slide in the cover to crush the plasta-gauge while torquing the bolts.

Remember be kind.
Interesting approach! It would likely work, but you may have to use a spacer smaller than the original so that the Plastigage would work. The largest Plastigage available covers 0.009-0.020", the shims are available 0.1-1.7 MM (0.004-0.67"), so if the original shim was less than 0.5MM you could do it without using a spacer with the Plastigage, otherwise you would have to get a spacer that would bring the clearance into the Plastigage range.

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post #40 of 47 Old Oct 22nd, 2006, 12:32 pm
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Another way to skin the cat?

Quote:
Originally Posted by dshealey
There is no way to check pre-load with the housing cover in place. I had thought that if the housing cover would slip over the bearing easily enough one could put in an extra shim, push the cover down until everything was settled in place, then measure the gap between housing and cover. Then you could put in a shim 0.002-0.004" thicker than the extra one used for testing.

(Disclaimer: I have never stayed in a Holiday Inn Express, but I have done 3 crown gear bearing replacements.)

Well, actually there is, or should I say that it worked for me? The method is to remove the preload shims and then measure the movement. With just a "little" heat on the housing cover the bearing will slip in the bore fairly easy.

Let me explain:
See Pic 1.

Tools: Dial indicator w/ magnetic base, two small pry bars, SMALL soft face hammer, two small wood blocks to use as pry points, and a heat gun and a non contact temp reading device (not shown)

Setup: Drive unit assembled without housing O ring, hub seal, and preload shim(s), with or without pinion installed, parts lightly oiled is OK but CLEAN, CLEAN, CLEAN! Flat piece of steel bolted to the caliper mount holes to land the magnetic base on, two bolts screwed into the hub to use as pry points. Optional: Large "old" bath towel to place the assembly on to protect the finish.

The Prep: On the three I have done I've found that it didn't require much heat on the housing cover to allow the bearing to slip in its bore. Above 105 deg. F seemed to be sufficient . YMMV. Warm the housing cover. Take your time. Too hot to touch is way too much. Just enough to allow the bearing to slip in the bore and then just a little more.

See Pic 2.

The Deed: Put the magnetic base on the bolted on platform, place the dial indicator spindle on the center of the hub. Pry the hub assembly up in the bore.
1. Now take the SMALL soft faced hammer and "thump" the hub to seat it back down, 2. zero the indicator and pry up again. Read the indicator.

Do 1 and 2 numerous times to find the consistent reading. You will be able to feel the bearing slip in the bore and pull up tight against the housing when things are correct. Add some heat if deemed necessary. You will find that the consistent reading is the largest one. That is the end play. Add .002 to .004 in. to the dial indicator reading and that is the shim thickness to install. (And remember that the shims are metric dimensioned!)

A couple of notes:
When prying remember that we aren't trying to pull the bolts out of the hub. The pry bars used in the picture are short. Large screwdrivers would work fine.
When "thumping" the hub to seat the bearings we aren't trying to beat the $%!t out of it. (Did I mention SMALL soft face hammer?) Watch the dial indicator, it will show you when things are seated.

OK, so what about the heat? (I wondered too.) Took the assembly as seen in the picture and hung it above my little space heater in my workshop for an overnight "roast." The idea was to make sure that the internal componets were up to temp. When checked with the assembly heated (147 deg. F) the reading was less than .001 different. Not enough to worry about.

I think the reason for such a small change when heated is that the crown gear assembly is two pieces and one of them is aluminum (and expands more than if it were steel. (See Pic 3) The crown gear and hub are the same piece and made of steel.) The tapered roller bearing support (the cone shaped part) is made of said aluminum and is pressed into the hub portion of the crown gear as can be seen through the wheel bolt holes. (See pic 4)

On the last one I did (actually, the one shown in the pictures) has a few other issues dealing with possible reasons for failure. But that's another post!

HTH YMMV and Good Luck
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post #41 of 47 Old Oct 22nd, 2006, 1:25 pm
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That is a good way to do it too. The key, as you stated, is to have the cover hot enough to allow the bearing to slip up and down relatively easily.

Question? I thought the only real purpose of the aluminum part is to support the speed sensor ring. Is the small tapered roller bearing actually pressed up against it, or is there a shoulder on the axle shaft that the roller inner race is against? I would think that it should be against a shoulder on the steel axle shaft, as the aluminum heating and expanding could displace the bearing on the shaft slightly.

EDITED: Does anyone know if that aluminum part even exists on an '02-later LT that does not have the speed sensor?

Quote:
Originally Posted by Dman
(Disclaimer: I have never stayed in a Holiday Inn Express, but I have done 3 crown gear bearing replacements.)

Well, actually there is, or should I say that it worked for me? The method is to remove the preload shims and then measure the movement. With just a "little" heat on the housing cover the bearing will slip in the bore fairly easy.

Let me explain:
See Pic 1.

Tools: Dial indicator w/ magnetic base, two small pry bars, SMALL soft face hammer, two small wood blocks to use as pry points, and a heat gun and a non contact temp reading device (not shown)

Setup: Drive unit assembled without housing O ring, hub seal, and preload shim(s), with or without pinion installed, parts lightly oiled is OK but CLEAN, CLEAN, CLEAN! Flat piece of steel bolted to the caliper mount holes to land the magnetic base on, two bolts screwed into the hub to use as pry points. Optional: Large "old" bath towel to place the assembly on to protect the finish.

The Prep: On the three I have done I've found that it didn't require much heat on the housing cover to allow the bearing to slip in its bore. Above 105 deg. F seemed to be sufficient . YMMV. Warm the housing cover. Take your time. Too hot to touch is way too much. Just enough to allow the bearing to slip in the bore and then just a little more.

See Pic 2.

The Deed: Put the magnetic base on the bolted on platform, place the dial indicator spindle on the center of the hub. Pry the hub assembly up in the bore.
1. Now take the SMALL soft faced hammer and "thump" the hub to seat it back down, 2. zero the indicator and pry up again. Read the indicator.

Do 1 and 2 numerous times to find the consistent reading. You will be able to feel the bearing slip in the bore and pull up tight against the housing when things are correct. Add some heat if deemed necessary. You will find that the consistent reading is the largest one. That is the end play. Add .002 to .004 in. to the dial indicator reading and that is the shim thickness to install. (And remember that the shims are metric dimensioned!)

A couple of notes:
When prying remember that we aren't trying to pull the bolts out of the hub. The pry bars used in the picture are short. Large screwdrivers would work fine.
When "thumping" the hub to seat the bearings we aren't trying to beat the $%!t out of it. (Did I mention SMALL soft face hammer?) Watch the dial indicator, it will show you when things are seated.

OK, so what about the heat? (I wondered too.) Took the assembly as seen in the picture and hung it above my little space heater in my workshop for an overnight "roast." The idea was to make sure that the internal componets were up to temp. When checked with the assembly heated (147 deg. F) the reading was less than .001 different. Not enough to worry about.

I think the reason for such a small change when heated is that the crown gear assembly is two pieces and one of them is aluminum (and expands more than if it were steel. (See Pic 3) The crown gear and hub are the same piece and made of steel.) The tapered roller bearing support (the cone shaped part) is made of said aluminum and is pressed into the hub portion of the crown gear as can be seen through the wheel bolt holes. (See pic 4)

On the last one I did (actually, the one shown in the pictures) has a few other issues dealing with possible reasons for failure. But that's another post!

HTH YMMV and Good Luck

I don't want to achieve immortality through my work...I want to achieve it through not dying.

David Shealey
Dandridge, TN
EX: '01 Black LT, BAT BYKE (Totaled at 110,000 miles)
IBA SS, BB, BBG, 10/10ths.
No bike now, but maybe in the future.

Last edited by dshealey; Oct 22nd, 2006 at 1:39 pm.
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post #42 of 47 Old Oct 22nd, 2006, 2:31 pm
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Smile I wonder if they were concerned with the weight?!!

Quote:
Originally Posted by dshealey
Question? I thought the only real purpose of the aluminum part is to support the speed sensor ring. Is the small tapered roller bearing actually pressed up against it, or is there a shoulder on the axle shaft that the roller inner race is against? I would think that it should be against a shoulder on the steel axle shaft, as the aluminum heating and expanding could displace the bearing on the shaft slightly.

The "cone " shaped portion (axle) of the crown gear assembly is entirely of aluminum as far as I can tell. (Have the drive assembled and ready for install or I'd go look)

Pic 1. The Speedo ring in the picture is off of its mount area. The bearing ID is a bit smaller than the ring and is pressed to a shoulder above the ring on the axle

Pic 2. The face of the axle is faced (machined) except for the triangular shaped indent in the center which is raw cast.

Pic 3. If you poke a screwdriver into the center hole of the wheel mount hub you will find a void to the bottom of the tapered bearing stub of the axle.
If you drop a magnet in there it doesn't stick to anything.
Look at this picture and understand why there is a warning in the service manual concerning the length of the wheel bolts. Can you imagine the preload problems you would have if you used too long a bolt and "jacked" the aluminum axle out of the crown gear hub!


Quote:
Originally Posted by dshealey
EDITED: Does anyone know if that aluminum part even exists on an '02-later LT that does not have the speed sensor?
I'll SWAG this one. The aluminum axle is still there but I'd bet that the mount diameter, shoulder for the ring, and the ring itself isn't.
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post #43 of 47 Old Oct 22nd, 2006, 3:25 pm
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Now I see, the second picture shows the aluminum part also supports the roller bearing.

Now I am wondering if that was not an attempt to equalize the expansion rates a little so that the pre-load does not decrease much when the whole final drive gets hot?

I don't want to achieve immortality through my work...I want to achieve it through not dying.

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post #44 of 47 Old Oct 22nd, 2006, 4:24 pm
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Smile Sounds good to me!

Quote:
Originally Posted by dshealey
Now I am wondering if that was not an attempt to equalize the expansion rates a little so that the pre-load does not decrease much when the whole final drive gets hot?
(Another great mystery to ponder as I lay awake some night.) (Or not!)
That answer to your wonderment (is that a word?) is probably in the same place as the answer as to why they use a ball bearing to carry the hub in the first place.

Suppose? (LOL)

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post #45 of 47 Old Oct 22nd, 2006, 7:35 pm
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I'm sure expansion compensation is why there's an aluminum shaft.

My guess on the radial ball bearing choice for the crown bearing is that there are no large tapered roller bearings with a cross section that light. It has to be a good example of a design corner that engineers occasionally get painted into. The blind assembly with the crown bearing being a slight press fit on the OD doesn't help when determining the operating clearance.

One thing bothers me. I understood that single row radial ball bearings have a somewhat indeterminate amount of axial clearance. If so, that would make the thrust preload setup of this arrangement difficult and subject to measurement variations. That's why I would have leaned towards an angular contact ball bearing for this application - although it would be at the expense of radial load capacity for the same size assembly.
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post #46 of 47 Old Oct 22nd, 2006, 9:44 pm
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Quote:
Originally Posted by niel_petersen
I'm sure expansion compensation is why there's an aluminum shaft. ---------------------------
Reverse engineering is a real pain, isn't it! Always trying to guess what was on the other person's mind.

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post #47 of 47 Old Nov 15th, 2006, 9:32 am
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Did you report the final drive problem to the NHTSA? There are lots of stories on the internet about BMW final drive failures but very few have been reported to the National Highway Traffic Safety Administration. Of those reported, the specific component(s) which allegedly failed vary to the point that there is no clear cut culprit on record.

If you have had such a failure, I urge you to report it and include specific details that will indicate a pattern of failure if there is one. This is the only way that I am aware of to direct BMW AG's attention to the perceived problem.
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