Final drive failures - Root Cause

Discussion in 'GS Boxers' started by oughtsix, Jul 28, 2020.

  1. oughtsix

    oughtsix Reverse Engineer

    Joined:
    Oct 11, 2013
    Oddometer:
    625
    Location:
    NELA
    I dabble in industrial reliability, Root Cause Analysis, etc. Not that I'm good at it, but even a blind squirrel finds and acorn sometimes. That said, I'm just baffled why Final drive failures are still an issue all these years later. It's almost expected, which is less surprising. Hopefully this won't degrade into a pissing-match-turned-name-calling session only to get punted downstairs, but I'll take that risk. My position is that these failures are not unusual, and that is interesting. So I did a little reading.

    I determined that a common, if not THE common failure is to the large single groove ball bearing, measuring 85x120x18mm or somesuch. Failures seem to be noticed after damage to seal occurs, but not always. In many cases, it seems as though the retainer damages this seal, but perhaps not always. I am suspicious of lubrication in both cases. Stay with me.

    I later determine that it is a commonly available (to industry) SKF or FAG bearing, but may be cross-referenced to any number of other makers. I also happen to have a copy of the SKF bearing installation and maintenance guide on my desk, so I flip it open to the lubrication section Page 87 HERE

    Get ready to check my math.

    Using a 102.5 mean bearing diameter, and 150/70-17 rear tire, I get 933rpm at 70mph, and 1197 rpm at 90mph, which according to this chart, I say means that you need a lubricant with a viscosity between 10 and 15 mm^2/s cSt.

    upload_2020-7-28_15-12-35.png



    The next table gives ISO grade requirements at operating temp, I used 25-60c as a good range, although that may be a tad low. What do see is that an ISO 22 (SAE 75w is very close) or so is recommended. The chart assumes a VI of 95, and several of the gear oils I reviewed showed VI well in excess of this.


    upload_2020-7-28_15-17-28.png

    My assessment at this point is that BMW designed a gearbox and specified a fluid appropriate for the gears but not for the bearings, especially when cold, intentionally or otherwise. My thought at this point is that a thinner gear oil with high pressure additives (moly?) would extend bearing life while not compromising gear life. Run-to-fail is a legitimate maintenance strategy, and perhaps the egg heads back in Germany decided that the bearings were cheaper than the gears, so f*$% em.

    Looks like a straight weight synthetic may serve the best in this application, still researching to see if that exists.

    Feel free to shoot holes in this. I assure you, nothing you can think of will offend me, and I'm all about learning.

    P.S. Still want a GS.
    #1
    Andrew, Biggesthead, cnmjr123 and 4 others like this.
  2. Lead Wrist

    Lead Wrist Mehr Gelände Weniger Straße

    Joined:
    May 26, 2007
    Oddometer:
    7,102
    Location:
    Zer0-Zer0-Zer0-Zer0
    ^ Which platform are you referring to as "still an issue all these years later"?

    Not all FDs are created equal...
    #2
    C3trevor and Callisto224 like this.
  3. oughtsix

    oughtsix Reverse Engineer

    Joined:
    Oct 11, 2013
    Oddometer:
    625
    Location:
    NELA
    True that.

    I guess I'm speaking to the 1150 and 1200s. I'm early in my reading on this, and the bearing measurement quoted above is for the 1150 machines.
    #3
  4. Callisto224

    Callisto224 Long timer Supporter

    Joined:
    Jan 5, 2010
    Oddometer:
    7,103
    Location:
    GA
    Haven't heard much about FD failures in years, unless it's an older model.

    I thought this issue was resolved around the 2008-2009 model years.

    :dunno
    #4
    JimVonBaden likes this.
  5. Zuber

    Zuber Zoob Supporter

    Joined:
    Sep 28, 2004
    Oddometer:
    6,738
    Location:
    West of the West, Oregon
    I did a similar analysis on the 'dry tube' drive shaft u-joints when they were introduced in 1988. The new 'lubed for life' joints only had a simple soap based yellow grease with no means to replace the lube. My analysis put the life span at about 20k miles.

    The OP's analysis is apparently for the R1200 rear drives from 2005? to 2016?
    #5
    Dale402 likes this.
  6. Lead Wrist

    Lead Wrist Mehr Gelände Weniger Straße

    Joined:
    May 26, 2007
    Oddometer:
    7,102
    Location:
    Zer0-Zer0-Zer0-Zer0
    Well, the issues are definitely still present with 1150s - I believe there was one-two in past few months on later '05-'06 1150s documented somewhere on the forum...

    As for R1200s, the frequency of the issues was reduced after "life time fill" of FD oil was removed and qty of oil in FD reduced down to 180ml (from 220ml) and venting was added.

    LC GS/As were introduced with reversed FD position, same as K-bikes prior, and that platform hasn't had reported issues IIRC...
    #6
    Biggesthead, Callisto224 and oughtsix like this.
  7. yaycep

    yaycep Been here awhile

    Joined:
    Jun 9, 2014
    Oddometer:
    463
    Location:
    Freiburg, Germany
    Very interesting information. But, your initial assumption that the FD bearing will run non-stop at 70-90mph on the wheel seems a tad off to me.
    #7
    scottdc and oughtsix like this.
  8. lewisjr1

    lewisjr1 Long timer Supporter

    Joined:
    Sep 26, 2008
    Oddometer:
    5,707
    Location:
    DC metro
    There were anecdotal claims that 75w-140 (or whatever) "high performance" gear oil in 1150s could lead to higher risk of FD bearing failure than the factory recommended 75w-90. For this reason, I always stuck with the latter viscosity.

    Lots of moaning & groaning, plenty of anecdotes, but never any real statistics. BMW is not about to let that info. out of its system, if indeed they even tracked it.

    From the perspective of the mfg., so long as failures within warranty weren't wildly expensive, the FD replacements were just the cost of doing business. Literally.
    #8
  9. oughtsix

    oughtsix Reverse Engineer

    Joined:
    Oct 11, 2013
    Oddometer:
    625
    Location:
    NELA
    That's a good observation. My assumption was that a GS will spend much of it's life muching miles. Perhaps a better assumption is an average of 50mph. That doesn't change the conclusion very much.

    Maybe a better angle of attack is:

    Under what condition does the bearing experience the most load (both in the case of radial and axial load)?

    Perhaps we wind up back at the conclusion that a quality 75w-90 synthetic is best thing commonly available.
    #9
  10. The Fabricator

    The Fabricator I didn't know it wasn't possible so I did it.

    Joined:
    Mar 30, 2018
    Oddometer:
    214
    Location:
    Petaluma, Ca.
    Looked at your post, looked at SKF pub [saved same for future befuddlement].
    You suggest a thinner lubricant to benefit the bearings as the present specified lubricant is thick to meet the requirements for the gears.
    I'm trying to think why a thick [high viscosity] lube wouldn't provide sufficient film strength for a rolling ball.
    What is the problem with too high viscosity?
    Too much friction is one [mechanical loses].
    #10
  11. vagueout

    vagueout Long timer

    Joined:
    Mar 3, 2010
    Oddometer:
    4,483
    Location:
    sydney, east
    Much debate on these over the years and i agree with Oughtsix that it should not be an issue, BMW have been making shaft drive bikes since 1923. In the case of the 1100/1150 final drives i believe early failure was due to incorrect shimming at the factory. The good news is that the 1100/1150 FD is a doable rebuild for the home mechanic. I did my 1150 FD as a pre-emptive with about 100,000 km/ 60,000mls, new big bearing and seal, worked out the shim requirement using the strips of solder method (very easy) and found the factory shimming was correct. The later 1200 FD not nearly as straight forward to re-build. In my 1150 i always used straight 90 gear oil with a squirt of moly additive. My two cam head 1200 bikes i use a 75/90 synth oil. Oughtsix's suggestion of a lighter oil? More informed minds that mine will have to debate that. Maybe that was the answer all along.:*sip*
    #11
  12. oughtsix

    oughtsix Reverse Engineer

    Joined:
    Oct 11, 2013
    Oddometer:
    625
    Location:
    NELA
    Two things here:
    1. I don't understand the relationship between film thickness and viscosity (resistance to flow). It may not be as straightforward as it seems. Especially in the case of multi-grade oils (75w-90, et al.)
    2. I think a potential problem with too-high viscosity is low flow. Especially when cold, but of you use a multi grade oil that behaves as a 90 or 140w at operating temp...it's even worse...?


    Makes me wonder about a sealed version of this bearing. This is not a high stress application, and I can't think of a single reason that it has to fail.

    *Shuffles off to research.

    ETA if anyone has a removed bearing I'd love to check it out, failed or not.
    #12
  13. ultane

    ultane sqeezin the bag

    Joined:
    Feb 20, 2008
    Oddometer:
    2,884
    Location:
    The dry side of the blood brain barrier
    IIRC, there was a group of the early 1200 final drives that were found to be improperly shimmed at the factory as well. This was discussed many years ago, by many, much smarter than me.
    #13
    LAFS likes this.
  14. AntonLargiader

    AntonLargiader Long timer

    Joined:
    Aug 28, 2003
    Oddometer:
    6,714
    Location:
    Charlottesville, VA
    Where is the bearing loading in your original assumption?
    #14
  15. oughtsix

    oughtsix Reverse Engineer

    Joined:
    Oct 11, 2013
    Oddometer:
    625
    Location:
    NELA
    Where should it be? I’m not qualified to say, but the static and dynamic ratings looked more than sufficient. I assume that is radial, and the tapered bearing handles any axial loading.

    setup is an interesting point to consider. There are plenty of shaft drive ssa bikes without this problem, so the overall design should work.
    #15
  16. ROAD DAMAGE

    ROAD DAMAGE Long timer Supporter

    Joined:
    Jun 3, 2007
    Oddometer:
    3,238
    Location:
    Steamboat Springs, COLORADO
    Popular misconception going on here ....................... there were lots of the Hexheads that did come with SEALED crown bearings.

    It's my understanding from guys that wrench on them a lot, that BMW went back and forth a few times on how they did this.
    I've had an 05' that had a sealed crown bearing and have had two 07's that were sealed as well.

    So .................. those sealed bearings are completely isolated from the final drive oil bath. :lol3
    The only thing that the FD fluid was lubricating was the ring and pinion, the outer beveled bearing, and some rider's imaginations.

    I've heard guys go on around a campfire for 30 minutes telling just how great that Moly/Motul/Valvoline/etc. and how that has made all the difference. In reality, their chosen lubricant had NOTHING to do with their crown bearing longevity.

    I agree with ought six .............. lots of shafties out there with NO bearing problems. :scratch :dunno :augie :confused
    BTW, one of my 07' GSAs crown bearing failed at 142K.
    Either one of the balls or the race had just begun to lose some of it's plating.
    I caught it real early and loaded it up in a Uhaul and drove it back to CO, so it wasn't destroyed.
    #16
    davegaz and darmahman like this.
  17. yaycep

    yaycep Been here awhile

    Joined:
    Jun 9, 2014
    Oddometer:
    463
    Location:
    Freiburg, Germany
    It’s different everywhere for sure, but my Nav usually reports around 50 km/h on average. (Have you ever seen a 20 sign? In kms! I have one, literally next door! Friggin’ Germans!)

    The difficulty IMO is not the average but in the deviation. You’d expect the same lubrication/heat dissipation performance from standstill up to, say, 130mph. That’s quite a range. Seemingly very straightforward stuff can get pretty tricky when you scratch the surface a bit.

    Don’t get me wrong, btw - I’m anything but an expert on this (or on anything, really :D)
    #17
  18. eri

    eri Been here awhile

    Joined:
    Jan 5, 2018
    Oddometer:
    602
    Location:
    ak,nz
    at 11min this is a long way to say bmw final version of the 2003-2012 final drive had quite a few internal differences as well as the eternally obvious venting

    main bearing in the fd oil bath seemingly a big one

    #18
  19. pistole

    pistole Long timer

    Joined:
    Jan 11, 2013
    Oddometer:
    2,242
    Location:
    earth
    the OP's thread is premised upon a theory that the final drive's bearing failure is caused by the type of oil used in the drive.

    I think that that is probably not a correct assumption.
    #19
    ROAD DAMAGE and JimVonBaden like this.
  20. BigMac75

    BigMac75 Adventurer Supporter

    Joined:
    Oct 16, 2018
    Oddometer:
    29
    Location:
    Oklahoma City, OK
    I am asking because...
    1. I do not know...
    2. I own a new to me 2015 GS Adv with approx. 44K miles, and am concerned it will happen to me...

    Is there a model year in which this stopped being a problem?
    Has the problem been engineered out of existence? Or this a potential liability that can happen to current iterations of the GS/GSA family?

    I am not looking forward to the prospect of my final drive committing seppuku while i am on the road riding.
    #20