How to do a "shaft spline lube" on a monolever K100/K75

So you've bought yourself one of those silly BMW motorcycles with water cooling, more than one cylinder and a lovely maintenance free shaft drive that people on the Internet rave about. Then you did a little reading and found that this maintenance free shaft drive is not quite so maintenance free. Bit of a bugger innit? Good job some anonymous hero has written this definitive* guide to help you on your quest.

*Disclaimer: Some bloke did this in his front garden in an afternoon and had no real idea what he was doing. There may be easier/more technically correct ways to do this.

Step 1
Stare at the back of the motorcycle.

Oh dear. Oh no. What crazy German gubbins lies within? Why didn't you just buy a chain driven bike instead?

Step 2
Begin by removing the right side panel.

I'm not even joking. This will let you get to the top mounting bolt for the shock later, which you will need to undo slightly so that the shock can be pivoted out of the way.

Step 3
Lift the seat up, undo the two nuts holding the number plate bracket in place, undo the two screws holding the number plate in place, and remove the whole sorry lot. Then remove the rear wheel.

The ease with which this can be done (aside from getting the plate out of the way) is possibly the one serious upside to owning a shaft drive bike. Enjoy this convenience as best you can.

Step 3b
I took this opportunity to knock the pins out of the rear caliper a bit, grease them up and knock them back in. This is optional but recommended as I had a right nightmare of a job getting the pins out of one of the front calipers a while back, it was so bad a Dremel and a hammer were both employed.

That's definitely better.

Step 4
Pop the ABS cable grommet thinger out of its holder and then undo the two bolts that hold the rear caliper in place, then tie (bungie) it somewhere out of the way.

Step 5
We need to free the speed sensor thing from its snuggly home. This, right at the back:

It is held in place with a Torx bolt, which is neat. Mine was also quite heavily corroded into place, which was less neat. You may notice the sensor is surrounded by crud, this will all want to fall into the final drive unit the moment you pry the sensor out with a screwdriver. Happy days.

I plugged mine with kitchen paper, which I soaked in oil in a vain hope that the dirt that had fell in would stick to it. I don't know if any of it did but it made me feel slightly better about what just happened.

Step 6
Undo the top shock bolt that you uncovered right at the start.

Now find something to put under the swingarm to hold it up for when you undo the bottom shock mount. If you let the arm fall to the floor there is a rubber boot that can be damaged and then you'll get water in your shaft housing, which will wash away the grease and corrode everything. Most people seem to use wooden blocks, I used a scissor jack.

Now undo the lower shock nut bolt and, errr, wiggle the shock off the stud? Not in my case..

The lovely British weather has conspired to weld the nut to the stud. This actually made the job quite a lot easier! Tie/bungie the shock up out of the way, it is useless now.

Step 7
I got a bit excited with the amount of progress happening and stopped taking pictures for a little while.. Basically, with the arm still supported, find a strong allen key and a bit of bar and undo the four bolts that hold the final drive on to the end of the swingarm. This is quite awkward, the bolts may be quite tight/corroded and the use of an allen key means you're doing your best to round out the bolts but it's the only way. I would have loved to have used a bit and a ratchet but there isn't enough room for the head of a ratchet, so allen key it was. Yuck.

With the bolts out, pull the final drive off the end. Mine spewed a bit of gear oil over the floor and, weirdly, had silicone sealant around the inside to hold the oil in. I guess the final drive leaks a bit and someone decided it was best to keep it all in the shaft housing? This is probably a Bad Thing but could be normal, I dunno.

We can see a shaft, hurrah! But it looks a bit mullered.. Hurrah? Uh oh.

Keep the final drive unit upright otherwise the gear oil will fall out. Wooden blocks to the rescue!

Is that rust? And what's with all the slime?


Step 8
"Simply" pull the shaft out. The trick oft mentioned is to hammer the end of it to break the contact of the splines on the far end, and then just pull it out. I hammered and pulled with vice grips and hammered and pulled to no avail. Eventually I went full on and pulled with all my might, including shoving away from a small stone wall. This finally made it come out, what a game!

The gearbox drives the outside of the shaft, which then turns through a layer of rubber to reach the inner part which drives the final drive. I had no idea it was built like this, one can only imagine how horrendously clunky it would be if it was just all metal.

Step 9
Clean those splines! Clean them so good. Also dig the rust and slime out of the final drive unit, should yours be in a similarly dilapidated state to mine.

With the bits cleaned I could see why the shaft looked so bad from the outside - the splines on the final drive are quite heavily worn and their strange shape has mashed the shaft as well. The shaft looks really bad at the outer edge but looking further in the splines look much better with a lot more of the flat top left intact. I think this may be a result of the gear oil leakage washing the grease away and perhaps from the boot splitting and letting water in at some point. How else can I explain all the rusty sludge? With a slightly heavy heart I decided it was good enough and would put it all back.

Spline wear is a problem with the Monolever rear end in particular because the amount of up/down movement makes the shaft slide along the splines, and supposedly this is when they wear. If I find I need to replace the final drive because the splines are too far gone (you can't fix them yourself) I'll probably stick a 16v Paralever setup on instead. For now I'll console myself with the thought that at least it isn't a chain driven bike, with easily replaceable and affordable sprockets or standard chain size that I can get anywhere should I need to. Because this maintenance free shaft drive is much better, right? Right??

Step 10
Grab your special 60% or more moly grease (in the U.K. we only seem to have Castrol Molub-Alloy Paste TA, in other countries you may use Guard Dog or maybe get some old stock Honda Moly 60) and shovel it onto the universal joint and the splines that fit the gearbox output shaft.

That tube was £12! Faff with the shaft until it fits back on to the gearbox splines, you just have to get lucky. With it in place smother a load more expensive grease over the other splines:

Then smother yet more over the final drive splines and slot/bolt it all together while desperately trying not to let any of it fall over or get dirty in any way. I found I had to wrestle the final drive on quite a long way, as if the shaft had not slid up the gearbox splines as far as it should. But eventually it went, and the bolts even pulled the dowels through their corroded holes. Success looks like this:

Installation is the reverse of removal and all that. I have no idea what the torque figures are for anything, just do the final drive clamping bolts up as much as you dare with the allen key and bar combo and the rest you can't go too far wrong with.

Congratulations, you just lubed your final drive splines! Now do it every rear tyre change if you're a responsible owner or every 10K miles if you're a bit lazy. I left it 12K but I'm a terrible person, sorry to any BMW enthusiasts who may read this.