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Pinion seal woes: How I Learned to Stop Worryin' & Luv the flawed FD of my '04 K12GT

For the last 18 years I have used the same "Bel-Ray Hypoid Gear Oil" in the 80W90 grade - both in the transmission and the rear-drive. This Bel-Ray gear oil is RED and meets the requirements /specs specified in the K1200RS BMW shop manual and owner's guide (for both transmission and rear-drive). I never had a leak so had there was no need to try different color gear oil in both zones / areas.

Bought my K1200RS new in 2002 and except for the 1st inspection at 600 miles (1000 KM) done at dealer, after this for the last 18 years I have done all the maintenance myself. Since mid 2002, my K1200RS has never seen a dealer (except bringing them the wheels to mount tires in some occasion).

Depending on mileage done during a year (varies from 4,000 to 10,000 miles), I would change transmission oil about every 2 years and rear-drive oil every year. This tigher intervall for rear-drive was mainly a visual monitoring mechanism for metallic deposits in rear-drive. My K1200RS now has 97,000 miles (157,000 KM).

Although I have seen a few problematic rear-drives on K1200RS/GT and K1200LT (friends), mine has been fine all these years. Anectodal evidences from many large BMW user groups (and meeting at rallyes), shows that having a bad one is a crap shoot - many are good some are bad... The shimming and built tolerances of all parts is critical (amost an art) and the factory has not always been on top of things for the quality control.

Jean, your 'Bio' above helps explain why I've found your posts so informative and useful, since I joined this forum. ;)

Thanks for your thoughts, again. When I drain the Final Drive oil to replace it with the Bel-Ray, I'll be looking for the amount of metal deposits in the oil and will snap and post a pic. My local dealership mechanic told me that the metal particles can make the pinion bearing wear, which is what eventually causes the seal to leak. So there may be some correlation between how heavy the metal loading is and whether a particular FD pinion seal leaks.

Because I've owned this 16-yr-old bike for only a year, unlike you I don't know the prior history of maintenance and/or abuse of this FD unit...

So, about 2½ weeks ago, before Northern California burst into flames, I set out on a solo 10-day motorcycle tour of points north of the Bay Area. Ranging as far north as Medford, OR and east as far as Yerington, NV, it was a great clockwise loop through counties with names like Humboldt, Trinity, Siskiyou, Shasta, Modoc, Lassen, and more. My intention being to make my nightly accommodations a mix of camping and hotel stays, my beloved ’04 K1200GT was burdened with more gear than I’d previously carried on such adventures. Wedged between a too-tall tank bag and a large duffel lashed across the rear seat and hard cases, I had a wonderful time on some of the less-beaten twisty byways up that way. (Pix in future posts, if anyone’s interested.)

Anyway, by the morning of Day 4, I realized two things: (1) undeniably, my front tire was much balder, after 3 days of fun in the mountains, than I’d anticipated when, two nights before departure, I paid it my first glance and, stoking my chin, sunnily opined that it would be… enough rubber to make it through the trip. Clearly, I had miscalculated. And (2), the messy streaks on my swingarm might not be just the residue of the misty rain I’d encountered the evening of Day 2, up in the redwoods along the 101 corridor and on Hwy 36 headed inland. It was looking, well… like something that had wafted up from the wet road surface and mixed with the dirt I’d acquired thus far. Again, I was wrong as to the source of the mess.

Fortunately, the plan for Night 4 was a hotel stay in Medford, and the town is big enough to host a BMW dealership – Hansen’s – which I have to plug here as a little family-operated gem. I pulled in to confirm my suspicions about the state of my tires and to throw myself upon their service department’s mercy as to the shoehorning of a tire change-out into their schedule. Happily, they worked me in. And, as all good techs do, they did a high-level inspection, informing me that (a) I had about 20% left in my rear brake pads, and (b) that mess on the swingarm? A leaky pinion seal. I vaguely recalled hearing, years before, that this is a known thing with these bikes. If I haven’t lost your interest at this point in the tale, hopefully some of you are grinning and chuckling and nodding since you know this all too well.

For the trip’s remaining six days, I monitored the state of things back there, periodically snapping pix, then cleaning it off to see how long it would take for the oily film to reappear. I was actually encouraged by the fact that hardly any more film appeared during the remainder of the trip, despite days of 90+ degree temperatures and sustained backroads cruising well into triple-digit speeds.

Upon returning home, I perused the K-bike forums for info and anecdotes about leaky final-drive seals and came up with a mixed bag: opinions and stories ranging from Oh-is-this-gonna-cost you! to Mehh… it’s not so bad: clean it up and monitor it, but keep riding; you’ll be fine for many more thousands of miles. Given my tendency to hope for the best even as I fret and stew about such things, I had intended to follow more of the latter course.

Meanwhile, reading up on FD maintenance and repair in the Clymer, I was daunted by the need for a number of special tools and a heat gun to break free Loctited fasteners, some means of fixturing heavy parts, and so on. Which probably had something to do with my decision to see no evil and hope for the best. Oh, and this was bolstered when I snipped the zip ties and rolled back the rubber boot, expecting to find teaspoons of gear oil sloshing around in there and, worst case, telltale signs of fouling farther up the swingarm, suggesting it might be worse than a pinion seal that was going. The area under the boot had but a very fine film of oil and looked surprisingly clean.

Anyway, the see-no-evil plan changed today when I dropped by San Jose BMW, where I hadn’t set foot in over a decade (long story), to be greeted by their cheery and helpful staff. A cursory glance at the swingarm-mess photo that I’d snapped on Evening 4 was all the manager needed to confirm that no, this was indeed a leaky pinion seal and it’d be best not to ignore the issue.


On the bright side, after I gave him a sketchy idea of my rudimentary level of competence turning wrenches, performing routine maintenance on the K12, he waxed encouraging and supportive of me having a go at disassembly, at least, and talked me through a few of the preliminary steps.

…Which brought me back to the Clymer for a second read-through of FD work, and brought me here to ask the first of what promises to be numerous questions. And, also, to write the first of a series of posts reporting progress and pitfalls as I delve, heart in throat, into final drive repair (clearly, for the first time in 14 years of owning two of these bikes) and plead for sound advice and wise council when I inevitably get stuck in the days ahead.

Ok, Sooo

With all that as preamble, I’ll confine the remainder of this long-winded post to one question for the Collective. For those of you who own a hard copy of the Clymer manual, I’ll reference page, Step, and Figure numbers, as appropriate.

Q1: Obviously, the first challenge is to remove the FD from the bike. In the end, I may not be able (or willing) to carry out all the complex surgery required to actually disassemble the pinion gear assembly and replace the seal. But if I get the FD free as a unit and take it to the dealership, that alone should save me some labor costs. It’s also an option at that point to have the shop break down the entire FD unit and service/replace all three seals. Or simply to swap in a previously-refurbished unit. More discussion to come on that, I’m sure!

Meanwhile, my first question is about the tooling required to separate the swingarm from the FD, i.e., to remove the fixed and free bearing journals (Clymer, p. 417, Steps 11-12, Figs. 11 and 13). For this, special tooling is required. My question is, Why? Referring to the Clymer text, this tooling is either BMW P/N 33 6 641 (see p. 415b) or a DIY fabrication involving welding two sockets and a connecting plate together (p. 416, Fig. 7). This tool is to be used in the disassembly as shown in Fig. 14, p. 417, to perform Step 11, p. 417. Having seen BMW P/N 33 6 641 on eBay, I think I understand that the idea is that at some point the 12mm Allen bit has to be positioned inside the 30mm socket, to avoid loosening (or tightening) both the locknut and the free bearing journal simultaneously. So the bore of the socket must be unobstructed, to pass the hex bit through it, and that’s the reason that the torque-application device (ratchet drive, breaker bar, etc.) can’t snap directly into the socket. In the DYI tool, the torque is applied to the 2nd smaller socket welded to the 30mm socket, leaving the latter’s bore clear. In the BMW tool, the 30mm socket’s wall is cut away, permitting access to its bore (for the 12mm Allen) from the side.

Can anyone please confirm or correct that understanding?

Further, consulting Fig. 14 (p. 417), I don’t see that simultaneous access to the locknut and bolt is actually needed for disassembly. And, though I haven’t studied it in detail, it seems that the need for this action occurs only on reassembly of the swingarm/FD linkage, on p. 420, Steps 18-20 and Fig 25.

Can anyone please tell me if I have this right, or I’m missing anything?

Also, if anyone has experience using the BMW tool for this, can you please comment on your experience with it? I’m not a welder and can’t fabricate the DIY tool myself (though I may be able to cajole a friend to make it for me). I might be willing to buy the BMW tool on eBay, but I vaguely recall, in my perusal of the forum threads, some discussion of the drawbacks or difficulties associated with using the BMW tool.

Finally, if any of you who have read this far have actually performed the pinion seal replacement yourself, can you offer me any general, high-level guidance at this point? Something along the lines of either:

(a) If you don’t have auto-mechanic experience and a well-equipped shop and comfortable workspace, you may be getting in over your head. Seriously consider opening your wallet and extracting a sizable wad of cash to let the dealer do it.

(b) You can do this! Take it slow, be systematic, study and follow the Clymer procedure rigorously, document your steps with photos and video notes, work carefully, and you’ll be fine. And you’ll be filled with the satisfaction that you tackled and mastered this elaborate but far-too-necessary process for dealing with this particular design weakness of these bikes.

Please, save any detailed comments or instructions, notes, or diagrams for a bit later in this journey, if they aren’t germane to the 50,000-ft perspective I need at this point, when deciding whether (a) or (b) is the narrative closest to my reality.

And, as always, many thanks in advance!

Best regards,

Sad to read this thread, as it mentions Hansen’s BMW in Medford, where I have frequented on many a pit stop from the Bay Area, and now it is burned to the ground.
Sad to read this thread, as it mentions Hansen’s BMW in Medford, where I have frequented on many a pit stop from the Bay Area, and now it is burned to the ground.

Odd as it is to respond 3 years after your post, as it happens I just read it and was moved by it.

I, too, was shocked and saddened to learn it had been lost in the fire - which was exactly a month after I came through and met them. I met Craig, Mark and Wade during my drop-in and Craig took the time to share stories of his decades as a fixture among BMW dealers. He told me they were one of the last family-owned-and operated dealerships in the country. What he was too modest to tell me was that Hansen's was rated #1 in the United States for Customer Service Satisfaction multiple times in their long 50-year history.

But, ya can't keep good folks down. They kept the business alive as covid raged and they improvised out of a temporary space in Medford. They came back to full-service operations in a new location, but I guess Craig finally had enough and if IIRC, sold the dealership at the close of 2022. Not sure if it is still operating under the Hansen's name...