In regards to a 1992 k100rs:

Hey everyone,

Well this sucks.  My transmission has taken a dump again.  If anyone remembers, I just recently replaced it (here's the link to my earlier forum post during the first replacement https://www.k100-forum.com/t7734-transmission-death )

The same thing is happening again but this time with 5th gear.  It's skipping, dropping out, etc.  It happens mostly while under load, but sometimes while just cruising.

Shifting is normal.

The transmission sounds a bit rumbly, crackly, and thumpy any time it's in gear.  The sound gets progressively worse from 1st to 5th, but is unnoticeable until the bike starts to skip/jump in 5th gear.

I've kept it oiled with Royal Purple 75w-90, and checked it frequently for cleanliness and level.  It was always clean and topped off.

This transmission had around 40,000 miles when I installed it, and since then, I've probably put around 8,000 miles on it.  It was perfectly smooth, silent, and great when I installed it a few months ago.  The original transmission had 113,000 miles on it, 15,000 of which I put on before it died.

I suppose I'm just lost as to what's causing this.  I wonder if I'm riding it wrong somehow.. (been riding for 6 years now).  Or maybe I've just been unlucky with my transmissions.  Although as Rick said in my original forum thread, transmission problems are rare.

Anyways, another transmission is on it's way from ebay.  It's a good thing these bikes are undervalued.. Transmissions are the same price as a new tire.

Anyone got any ideas / comments / I don't really know what I'm expecting.

I guess you would have to consider if any one single component has stayed the same , ie the drive shaft perhaps ? final drive ?

a good examination of the failed gearbox might be suggested , before putting a new one on .

I agree with Charlie.     I had a similar problem with first gear.  I pulled the box down and had a good look.  Not only did I find some broken teeth also found that some of the selector forks were bent as a result of dropping out of gear and a sloppy bearing. Not a bad effort as they are made of titanium..  You can see my journey HERE into the gearbox.

If I remember it was 1st gear last time and this time it's 5th so I would be inclined to be thinking that you may have picked up a dud.
With something like a transmission I will always pull it down before using it no mater what the seller tells you, however I do realize that to many that is a daunting task and not willingly done.
The one thing that can do big damage to these Getrag boxes is to change without using the clutch so I do hope you haven't been doing that.
If you are up to pulling it apart then I would suggest trying to make one good box from the two damaged ones you have.
Quite often all that is needed to start the thing on the road to the tip is to miss a shift or two and the fork bends a touch which makes it jump out sometimes and then before you know it's at it all the time.

@ charlie: I'll have a good look at the drive shaft and final drive for excess play and wear.  I suppose it's possible that play in those could cause gradual damage to the transmission.

@ Rick: it was 2nd gear last time, not that it really matters.  I never ever ever ever shift without the clutch.  I'm not comfortable doing it, so I don't do it.  I have the occasional screw up where I accidentally kick it in to first while sitting at a stop light and stall the bike though.  That's maybe happened once or twice in the 3-4 months this transmission has been installed.  I remember it sounded so good and felt so smooth when I first installed it, but suppose it's still possible it was a dud too? I had actually planned on taking my two dud transmissions apart and making a complete good one.  I'll use Alby's link to take them down.

Here's a question for you: When the bike is in first gear, the shift lever does not move down any more.  Is it the selector fork that keeps it from moving down, or some other 'fragile' part?  Also, when downshifting and it gets stuck between gears, is that also the selector fork, and any large amount of pressure on the shifter could cause it to bend?

Anyways, I bought another one.. it'll be here on friday, and it supposedly only has 25k miles on it.  I'll just pop it in and build another tranny in the mean time.

It's not the selector fork itself but that the drum cant rotate any further. Getting stuck between gears is what I mean by missing a shift and that can make the dogs of one gear push the sliding gear back and so bend the fork. Quite often it happens with the Ks from being a bit too gentle and not making a firm and positive shift, usually it just leaves the gear in a transient stage between the two gears and giving the lever another push does the job but if it happens when you are shifting hard then you can do damage.
When I was drag racing my Kawasaki if I missed a shift usually you lose so the racing is over for the day but I would rebuild the transmission from top to bottom because if I didn't then it would keep happening and take the fun factor away.

I was a bit freaked out by the idea of delving into my gearbox - but I did it and thoroughly enjoyed the process! Great fun, very interesting and highly rewarding. I combined the best shafts from 3 gearboxes and installed all new bearings and seals.  Have done about 2000km now (a guess as my odo does not work) with no probs other then an incorrectly installed output shaft seal. 

The biggest bit of advise, if you do decide to open them up, is to ensure you dont mix up or missplace the shims that go between the inside of the gearbox case face plate (or lid) and the shaft bearings. If you are going to be mixing and matching shafts and/or replacing bearings, this doesnt matter as you will have to redo the measurements to figure out what shims you need (if that sounds complicated, its not really - they are actually pretty simple and its very interesting to see how it works) I used a combination of the shims from the various boxes to get the thickness I needed based on my measurements. 

I didnt know that damage could be caused by shifting without the clutch, but its obvious I guess now that Rick mentioned it, as these GB's are very different to anything I have ever riden with and not like a 'normal' motorcycle gearbox. I used to get quite a few false neutrals mostly upshifting, due to me not doing it right. But now they are very rare and always when I forget Im on a BMW. 

I am still getting used to the shifting style of this box I must confess. Much less frantic and immediate with a longer throw than Im used to...not complaining, just different. 

Would like to know what the BSK guys have done to get such quick shifting, as heard in their onboard lap vid on youtube. 

good luck.

Would like to know what the BSK guys have done to get such quick shifting, as heard in their onboard lap vid on youtube.

just practice ....and maybe a little preloading  Floyd ...  youll get the hang and feel for it in time im sure

Little update:

The bike now skips in gears 2-5.  I lifted the rear wheel off the ground with a piece of wood under the center stand and got down next to the transmission to get a better idea of where the sound is coming from.

The rumbly / crackly / thumpy sounds seems to be emanating from the back right side of the transmission around the area where to drive shaft connects.  Does this tell us anything?

Can you disassemble the rear end to inspect the transmission output splines?  Or even remove the final drive and extract the drive shaft to inspect the corresponding splines at the U-joint?  They might be knackered.

Big update here:

New transmission came, popped it in (it was about an 8 hour pop..), and everything is fine again.  I took some pictures along the way of splines and such.  Also made a video for the final drive.

Broken roller bearing on final drive:
https://i.imgur.com/yEp4QXn.jpg

Doogered part of the roller bearing.  I cleaned it up and put it back for now:
https://i.imgur.com/j3czqah.jpg

'Fixed' roller bearing.. for now.. till I have time to get a new one pressed in.  It moves freely and feels just like the other one which is in good shape.
https://i.imgur.com/B7GHyd8.jpg?1

Drive shaft splines front end (cleaned up grease for ease of viewing):
https://i.imgur.com/kCEBcIp.jpg

Drive shaft splines rear end:
https://i.imgur.com/rMH5Ayv.jpg

Transmission output splines:
https://i.imgur.com/YJTJKmO.jpg

Clutch splines 1:
https://i.imgur.com/zQxKOah.jpg

Clutch splines 2:
https://i.imgur.com/TLOEc7Y.jpg

Final drive video:
https://www.youtube.com/watch?v=3eR0XXqtOwU&feature=youtu.be
I mentioned what seemed to be a little play in the final drive universal joint.  That could have just been the splined connection inside it that I wasn't aware of until after the video.


Everything looks okay to me, except that roller bearing of course, but then again, here I am on the forum seeking the knowledge of the experts.   
Thanks in advance.

Just so you know, if you click on the icon next of the large picture with the green + it will allow you to post the images directly in the thread. 

Find the youtube button....its the 2nd to the left of that one.

Oh cool, I'll remember that next time! I'm not great at this forum stuff beyond plain text.

Interesting read. Thanks to all the posters 

I've often wondered about the gb. I bought my RT nearly 5 months ago and the seller told me about how the gb was normally very clunky. I was sort of expecting that becuse I had an R75/5 some time back but I did find it difficult doing a smooth change without what I regarded a excessive clunking. I also found it in false neutral annoyingly too often.
Now I don't know if over the last few months Ive mastered the art of shifting with very little noise or it was the new clutch cable (which gave me the opportunity to adjust the clutch properly... I suspected it was out), but these days changing is pretty smooth. Ive found that using possitive action on the gcl helps enormously.