1200GS (K25, 2012): noisy final drive on cobblestones - or what?

[Zeebulon]

More or less from the beginning (2023), I noticed a nasty thunky sound from the back. Apparently it became louder over the last 10000 km.
It can best be reproduced on a cobbled road, or roadside grass. Here's the link to a short movie:

.

My airhead paralever (ok, it's HPN, regarding the power train it's more a 1150GS) is much quieter. Is this the technical progress...?

The bearings are tight and the wheel's not wobbling. According to an experienced shop floor master, who took a test ride on appropriate road surface, it's nothing alarming from the drive shaft or final drive. It sounds not "mechanical", more like as a big nut or wrench is clattering in the tool box. Needless to say I removed this completely, also I checked if anything was loose unter the luggage plate below the passenger's seat (which I removed also).

The rear suspension strut (it's ESA) is working correctly. If the bike is on the side stand and I raise it up and I bounce the rear up&down using my weight

, likewise no loud clunking noises.

Any ideas?

 

[botus]

bevel chatter - mostly the its slop on the 90 degree angle change between the pinion the shaft spins, and your crown wheel that gives the final gear reduction

running on surface's that allows the wheel to move back and forth (rough roads) or where you have the the throttle open and closed (traffic, nadgery maneuvering) can lead to a knock from the backlash between those two gears....

the noise you have is 100% normal - but it is horrific and isn't a good idea - never run on the stand in gear - some say on the stand, the shaft UJ angle is close to undesirable - and the acceleration / deceleration of the bad design of a basic UJ exacerbates the issue - its a reason front drive cars run a grown up constant velocity joint - way more costly - way more refined

then we have a cush-drive inside the gearbox - its on the output shaft and can fail and or contributes to the fun - its been an ongoing issue - some early ones around 2006 had issues and then 2008/9 it came back again - silly money complete gearbox output shaft is the fix there.

I'd suggest yours like mine is a combo of all three bits of fun arguing at the same time

NOTE:

later servicing rules and regs came in from 2025 - on these old ones they don't care so never changed anything - but the sensible thing would be to consider it for any 2004 or newer shaft BM bike - but for now all 2013 and newer twins have a remove and check the cardan shaft every 12k miles and then a mandatory shaft replacement every 37k miles

the bevel self destructing - can go from minor slop - well inside spec, to collapsed in 25 miles - mine did this at 40k miles this year

 

[Zeebulon]

So you say it's the play / tolerance (sorry, I'm no native speaker) between those 2 gears (pic taken from spare parts catalogue for R100GS 1992):

I never ran the engine on the stand in gear yet. But maybe I'll try, just to check if this gives that annoying clatter.

The "cush-drive inside the gearbox": did I get that correctly it's #1 in this image (input shaft)?

According to the mentioned experienced service technician he would also +/- exclude this assembly as origin of the phenomenon (it's not a problem yet, just tedious). But your assumption that several single points add up surely applies.

Which part do you mean with "bevel self destructing"? Could you please show me on MaxBMW ? Thx!

Remaining: why obviously new to the K25? Do the K50/K51 do the same? Why airheads, 1100 (259E) and 1150 (R21) not? Reduced flywheel mass inertia?
BTW: FD oil is 75W-140. Any conceivable alternatives / additives?

 

[botus]

the video has it running on the stand ?

yes re the part 1 in the box

the final drive bevel unit is renowned to reach end of life circa 60k miles - a bearing fails partly due to moisture attacking a bearing / design failing

the later unit with the breather is meant to last longer as that bearing is inside in an oil bath on the later design - but I had one of them with more slop than mine, noise and outside spec at 21k miles

and then some of the R-Ninety ones have the gear unwelded on the crown wheel hub - recall for those

its all part of the experience on offer with German engineering - one specialist in the UK strips and rebuilds - but the parts are big money and the unit has to be serviceable to rebuild with new seal and bearings and the costs are scary

who said new to the K25 ? the K50 and 51 have the new service schedule this year - I think the idea is we deserve to die coz haven't bought a new bike...

 

[Mistacat]

The op did not say what milage his bike has done.
The op`s bike is 2012 so has the later final drive with the bearing in the oil bath.
My 2012 has done over 110K miles on original final drive and does not have any play in the wheel , oil change 75-140w every 6K miles..

 

[Zeebulon]

the video has it running on the stand ?
...

No: for the recording I taped the smartphone to the passenger's footrest bracket and rolled over a cobblestone road.

 

[Zeebulon]

The op did not say what milage his bike has done.
...

82.000 km.

 

[Zeebulon]

Ok, so I just ran the engine on the stand in (2nd) gear: sounds awful in my ears (compared to my HPN with 1150 drive and FD). And this is 100% normal, botus?
I understand the adding plays/tolerances all the way through from clutch to rear wheel, but this sounds terrific.

Engine not running:

 

[botus]

mine sounds just like it - has done for 10 years - used to a bit quieter but not much - when the gits did the steel hub recall it got really nasty

you don't hear anything when riding

its a cross between a cement mixer, some large boulders and a worn out landrover defender

 

[Zeebulon]

mine sounds just like it - has done for 10 years - used to a bit quieter but not much - when the gits did the steel hub recall it got really nasty

Thanks, so it seems the old saying applies: "they all do that".

you don't hear anything when riding

Yes I do! Despite earplugs. Without: can't ride it.

its a cross between a cement mixer, some large boulders and a worn out landrover defender

 

[Zeebulon]

As for the different noise components / frequencies: if you can, try listening to the videos using a closed headphone - makes a big difference and is far more realistic.
Running while on center stand produced more "metallic, bright" noises (which I could accept/understand), while rolling over cobblestones is more that "rumbling, clunking" (see the consonants) which drives me nuts.

 

[botus]

yes when on the centre stand, the slop has nothing to damp its rattling - so you get a sharper metallic smashing of components into each other with wild abandon

whilst u may hear some noise from the rear bevel - the nasty chattering should never be audible under normal riding - I suspect - but prepared to be shouted down by those that have stripped it down and know - the steel hub managed to change the backlash slop - on mine it was from far to much to utterly crazy after they did whatever they did

I wouldn't be surprised to hear for bikes of x age and outside dealer servicing, (like I have found with most recall work) - somehow !!! you end up with extras - almost as if BMW UK expect dealerships to "magically encourage" some more workshop time to help recover recall costs

 

[Pukmeister]

I had a knock/chatter from my Hexhead FD whilst touring Italy years ago, road speed related so the faster I went the more it knocked. I had fears of driveshaft failure on the way home.

On further investigation at the roadside the metal spring clip that preloads/cushions the rear brake pads in the caliper had fallen out, allowing the pad friction faces to catch the rotating disk and rattle up/down in the caliper with a knocking sound/feel. Big sigh of relief.

An easy fix with a new spring clip for a few quid.

Might be worth checking yours ?

 

[Zeebulon]

I had a knock/chatter from my Hexhead FD whilst touring Italy years ago, road speed related so the faster I went the more it knocked. I had fears of driveshaft failure on the way home.

On further investigation at the roadside the metal spring clip that preloads/cushions the rear brake pads in the caliper had fallen out, allowing the pad friction faces to catch the rotating disk and rattle up/down in the caliper with a knocking sound/feel. Big sigh of relief.

An easy fix with a new spring clip for a few quid.

Might be worth checking yours ?

Recently I had to change my rear pads (worn), so I am sure that everything is ok down there. But one of my first supicions was indeed the caliper: became loose and rattles (guide bolts worn?) - but was ok.

 

[Pukmeister]

Recently I had to change my rear pads (worn), so I am sure that everything is ok down there. But one of my first supicions was indeed the caliper: became loose and rattles (guide bolts worn?) - but was ok.

Did you look up inside the caliper casting to see the big metal spring plate was still there? It clips into place but can rattle loose.

 

[Zeebulon]

Did you look up inside the caliper casting to see the big metal spring plate was still there? It clips into place but can rattle loose.