Hello,

Today i had a problem with my '91 K100 driveshaft, the grooves in the driveshaft worn out and I couldn't ride it any more. Out of the blue the rear wheel stopped turning when i wanted to drive off a red light. It showed no sign of dulling prior to this.. The bright side was that i had a refurbished driveshaft from the last time this happend (about 10 years ago) and I managed to get that and changed it on the side of the road. 
The thing is that i read in some topics on the forum that it should be lubricated? I am just wondering what exactly should be lubed? 
I mean should i lubricate the driveshaft grooves where the teeth of the differential hub enters in it? 

Like inside here? Where i painted red?  (this is not mine, i just found the photo on google to show you)


Is there a special lube or can i use just grease?

For the moment i did not use anything, because i did not have any grease (and also i didn't know if i should use any). 
However, in the "housing" of the teeth of the differential hub i did found some old kind of paste (maybe old greese), i couldn't tell. Should i remove it and clean it and add some new also in the housing, or just where the teeth enters those grooves in the driveshaft (like in the picture above), or where exactly?

I didn't think to take a picture of it to show you the condition of it, but i will do that if i have to add grease since i will remove it again... I will also try to take a picture of the teeth of the hub.

This is what i mean by the "housing" of the teeth of the differential hub (green marking): (again, not mine)




Can you please clarify?

Thank you very much!

You want to apply lubricant to the full length of the splines (teeth) on both the shaft in the differential and the internal splines on the driveshaft where you have indicated, as these are the areas that slide back and forth on each other. 

Clean all the old lubricant from these two surfaces before re-lubricating. Personally, I use a toothbrush to apply new lube as this allows me to work the lube into all the splines on both parts. You could use your finger if you needed to, but wear a neoprene glove of some kind. Apply a good even coat as best you can to all the splines, making sure you coat all the surface area of the metal. But don't use an excessive amount as it will just get pushed off when you reassemble.

I use Moly Lube TS60 Spline Lube that I buy from Ted Porters Beemershop in California, USA. I don't know what you would be able to purchase where you live. You will no doubt get other responses as regards type of lube (some owners use a custom mix of their own) and method of lubrication from owners who have had these bikes for many years, so they should be absolutely listened to.

https://www.motorworks.co.uk/molub-alloy-spline-paste-white-t-oia09338-1.html

My favourite and much closer to you. Don't forget that you need to grease the clutch splines too.

I use a 50/50 combination, on cleaned up splines, of Castrol Optimol TA and Honda's M-77 assembly paste, as recommended to me over two decades ago. I haven't had a spline failure on any moto yet. Be certain to also keep the input splines lubed at the clutch centre.

I clean and grease my one up once a year. It has lasted well. I wasn't aware that they let go suddenly without warning . I have learnt something new today.
Thanks.

Porto wrote:I clean and grease my one up once a year. It has lasted well. I wasn't aware that they let go suddenly without warning . I have learnt something new today.
Thanks.

They will if not greased. The splines wear so thin that they will suddenly let go all at once.

I had better grease the rear drive shaft.
Should I do the splined couplings at both ends?
How does the universal joint get lubricated?

I have an old tin of black goo, labelled "CrMo", which I inherited and I guess it's some sort of molybdenum paste.
I'm not quite game to use it.
I'm looking for Castrol Optimol, but can't find any in Australia.
Anyone here know of an available alternative?

Yes - do both ends of the drive shaft. The UJ is sealed, so don't worry about that. It would be ideal if you greased the clutch splines too, particularly if you don't know that they have been done. As long as you are using a good grease (similar to Optimol), experience has taught me the following:

- clutch and front end of the drive shaft every two years
- rear drive box every tyre change

That's on 11 - 13,000 miles a year. The reason for the difference is that there is next to no movement in the clutch and front of the driveshaft, so the grease doesn't get thrown out. If the wheel is off for a tyre change then it's only four bolts and ten minutes to grease the drive splines which do move front-to-rear a lot. These are the splines that willl wear and let go if not looked after. (Yes, I do grease the splines while the bike is in the tyre shop! I've been using the same shop for over twenty years so they know me well).

Thanks Dai.

So the front of the drive shaft, upstream of the uni joint, is what goes into the clutch centre?

Will the shaft assembly easily pull out from the clutch end?

For 1990 and later K bikes, the BMW recommended spline lube interval for the clutch/transmission input shaft is every 40,000 miles. (64,000 km)

https://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/maintsched/BMW.K.Bike.Maint.Sched.All.K.Bikes.pdf

Jordan5 wrote:Will the shaft assembly easily pull out from the clutch end?

The shaft will pull out easily from the clutch end when you remove the transmission to which it is attached.

Jordan53 wrote:Thanks Dai.

So the front of the drive shaft, upstream of the uni joint, is what goes into the clutch centre?

Will the shaft assembly easily pull out from the clutch end?

Gearbox has to come off to get at the clutch. It's not a difficult job but it is a complete ballsache.

OK, thanks folks.
I'm going on a couple of longish rides soon, so for now will get to just the rear splined coupling, which I gather is the critical one.

Jordan53 wrote:I'm going on a couple of longish rides soon, so for now will get to just the rear splined coupling, which I gather is the critical one.

If either one isn't lubricate correctly and at the appropriate interval, failure involving either one can stop you in your tracks.

If the clutch/transmission input splines are getting dry (needing lubrication) then a symptom of that is getting "false neutrals" when downshifting. I learned this on my second K bike which was the first one that I put any serious miles on.

It happened on my round the continent tour. I'd owned the bike for well over 15,000 miles so was used to its riding and shifting. I first noticed the false neutrals riding twisties as I rode down the California coast. Not knowing any better at the time, I wrote it off to lazy shifting on my part and just kept riding.  About 10,000 miles later, pulling away from a stop sign in southern Minnesota, about 1,200 miles from home, the bike made a short hideous grinding noise as the clutch splines failed and left me stranded with no power to the rear wheel.

I was later reading some posts by very experienced K owners over at the MOA forum which is how/when I learned that the false neutrals are a known symptom of dry clutch splines.

Several years later I did to fly-n-ride to purchase a K75C with about 80,000 miles in Idaho and ride it about 1.400 miles home to Washington. Sure enough, when I got going on my way home I noticed the familiar false neutrals on downshifts occurring. Since my prior K75's splines had lasted at least 10,000 miles with dry splines I wasn't too worried about and it and just rode it home.

Of course when I got it home the first thing I did was lube the clutch splines and, as expected, the false neutrals went away.

I'm pleased that there is no tendency to false neutrals on mine.
But I'm surprised that it's an issue with transmission splines at all.
On my 1975 R75 there was no such issue, nor on any car I've owned.
Has anyone looked into getting some oil in the swing arm?

Dai wrote:

Jordan53 wrote:So the front of the drive shaft, upstream of the uni joint, is what goes into the clutch centre?

Gearbox has to come off to get at the clutch.

Oh, yes - the clutch would be at the input of the gearbox, not the output. Silly me.

Dai wrote:there is next to no movement in the clutch

When you let the clutch out there is enough sliding under load to cause spline wear. The fact that unlubed clutch splines wear out is proof of that.

Do you think that the clutch plate doesn't move back and forth on the input splines when the clutch diaphragm spring is compressed and then released?

The front splines of the drive shaft are very different from the clutch splines in that they have a snap ring in them that prevents any sliding.

Does that snap ring have to be removed before the drive shaft can come out?
The swing arm needs to come off first?

The swingarm has to come off anyway to get at the forward splines. Depending on how it feels, the driveshaft will either come off relatively easily with a good heave or you may need a drift to separate it from the gearbox output shaft. If you do have a sticky driveshaft, punch it back on with a mallet before refitting the swingarm.

duck wrote:

Dai wrote:there is next to no movement in the clutch

Do you think that the clutch plate doesn't move back and forth on the input splines when the clutch diaphragm spring is compressed and then released?

IME not enough to scrape off the grease in under a couple of years, but then I really don't do anywhere near the number of miles that you do (can't find a jealous emoji so consider it inserted. If I did in a day what you do sometimes, I'd fall off the end of the island unless I turned round).

I removed the swingarm without much trouble.
The shaft assembly did need a good tug to get it to let go.
I made a mini- slide hammer to remove the right bearing end cap.
I was surprised to find the front splines seemed to be lubricated with normal grease.
However, everything is in excellent condition.
The rear splines might have had molydenum based paste, hard to know, but it looked like it had been applied recently.
I've no idea how I'll go with fitting the rubber gaiter. It must be possible, but not obvious how that's done yet.
I was using an old toothbrush to clean out the grease - a tricky job until I figured out I could turn the gaiter inside out for perfect access.

The taper-roller bearings in the swing arm have a fixed position on the right hand side, so it's easy to keep the original lateral location. My old R75/5 had both bearings adjustable, which might be useful but a bit of a pain to set wheel alignment from scratch.

If the front splines appear to have normal grease on, that's a very good reason to continue on to the clutch. The rubber gaiter just pushes back in. You'll probably find that it self-locates when you push the swingarm back on.

Install the gaiter on the swing arm and then put a little liquid dish soap on the lip of the gaiter to make it slide easily into place on the transmission.  The soap will dry out and help hold the gaiter in place with a tiny bit of stickiness.  Any soap on the outside will wash off the first time the bike gets wet so it won't attract dirt.

The drive shaft splines were treated to the tin of black, tacky stuff I had which was hand-labelled as moly.
I didn't have anything else to hand. But I think it's authentic, more convincing than the light grease that was used previously. I didn't manage to do the clutch splines, as time beat me. Fingers crossed, and I'll attend to it after my planned rides.

Fitting the gaiter to the swing arm is easy, but the method of installing the retaining circlip, according to instructions in the factory manual, was not getting results. I finally worked out to install the circlip to the groove in the gaiter first, then place the assembly as a whole to the swing arm - that was easy. I'm not going to trust the manual suggestions as being in perfect sequence any more!

Thanks for the installation suggestions. I used washup detergent between the gaiter and gearbox. I hope it found its own way into place. It's not possible to visually inspect.

I won't be trying my brilliant idea of introducing oil to the swing arm. There's a rubber damper on the shaft, which might get damaged by it.