Put the bike on the centerstand and remove hardbags (if any).
If the muffler is still hot, let it cool or cover it with something to protect your hands. The first thing is to loosen the two nuts that hold the fender on. These nuts are inside the rear tail section. You access them by lifting the seat and removing the rear compartment cover. Two plastic caps cover the nuts. Pry off these caps and then loosen the nuts with a 10 mm wrench or small socket wrench and 10 mm socket. Note that you only have to loosen these nuts. You do not have to take them all the way off. There are also two screws above the license plate that must be removed before the fender can slid rearward and off. The license plate will most likely have to be removed to get to these screws. After the screws are removed, slide the fender rearward and off. (The fender is the black plastic piece that the license plate fastens to.)
Next, remove the hubcap (if you have one) on the left side of the wheel by prying it off. This exposes the lug bolts. Remove the four lug bolts and slide the wheel out. Notice that there is a thin spacer between the rear wheel and the final drive unit. Be careful to note the location so this spacer making sure that it does not fall off the wheel.
Remove the bolts holding the brake caliper and then loosen it from the disk. Notice that the front caliper bolt holds a clip which retains the speedometer drive cable. Normally you can remove the saddlebag mount, but in this case we had to remove the right foot peg mount and saddle bag mount as one unit because we could not get the saddlebag mount loose from the foot peg mount. The saddlebag mount is attached to the rear subframe of the bike by two bolts and the foot peg mount is attached to the transmission by three allen head bolts. Be careful to notice the location of the brake pedal return spring before removing the foot peg mount. You can tie this combination of saddlebag mount and foot peg mount up out of the way or leave it dangling if it is not in the way.
Next remove the lower shock absorber nut. Put something under the swingarm to hold it up when the shock is removed. It is important to support the swingarm because otherwise the rubber boot between the swingarm and the transmission may be cut by the sharp machined edge of the swingarm if the swingarm is allowed to fall. If the boot is cut, moisture may enter the spline areas. This is bad. Pull the shock loose from the bottom mount, sliding out towards you. Pull the shock absorber up and out of the way as far as possible and secure it with a bungie cord stretched across the seat.
Remove the screw holding the speedometer drive cable on the final drive and pry it up and away. Move the speedometer cable off to the side, out of the way. Put a piece of masking tape over the speedometer drive hole in the final drive so nothing will fall in during the next steps. Now that the shock absorber is out of the way, pull the caliper off to the right side of the bike and bungie it out of the way. There should be nothing attached to the final drive at this point.
Loosen the four bolts that hold the final drive to the swingarm. Pull those bolts out and slide the final drive out to the back of the bike. Be careful not to drop the final drive. Sit on the floor with your legs under the final drive when you pull it. After you pull the final drive off, carefully set it aside, making sure that the speedometer drive hole is up, so the gear lube doesn't run out.
The exposed drive shaft extends out of the swingarm a little bit. Place a piece of wood against the drive shaft and give the wood a gentle tap with a mallet. This breaks it loose from the front spline in case it was stuck. In order to remove the drive shaft, first make sure the swingarm is parallel to the ground. Next, put a rag around the exposed rear end of the drive shaft and using a pair of Channel Locks over the rag, clamp down and pull the drive shaft rearward until it comes loose. It should take a healthy tug to get it loose. Remove the drive shaft from the swingarm.
Clean off the old grease from the splines on both ends of the drive shaft with mineral spirits, gasoline, or contact cleaner (disclaimer: this stuff is flammable, so use it outside and act accordingly) and an old toothbrush. Make sure you get all the junk out of the valleys of the splines. Wipe them dry with a clean cloth. Similarly clean the spline of the final drive, being carefully to keep the speedometer hole up at all times. The easiest way to do this is to have someone hold the final drive unit and slowly turn the brake rotor while you clean the splines.
Now, inspect the fit by mating the drive shaft spline to the rear drive unit. The fit should be tight, but loose enough to get the splines together and apart without being sloppily loose.
While you have the rear drive unit off check the swingarm for any looseness in the swingarm bearings by grabbing the swingarm and wriggling it side to side. It should feel tight and not loose in a side to side movement. Also move the swingarm up and down to make sure it moves freely, is not binding, and nothing is restricting the swingarm in its normal arc of travel. You should be careful only to move the swingarm within its normal arc of travel so as to not damage the boot.
Now you are ready to grease the splines and start the reassembly process. The red BMW spooge that comes in the cylindrical tube is good. Costs $7-10 and gives you enough for hundreds of lubes. Ask for BMW Lubricant #10 Part Number 95 00 9 000 190.
Put a little grease on your finger and apply it to the splines on the U-joint. Make sure you fill in the valleys of the spline. A large amount is not required since it is forced off when you push the drive shaft back on the the rear of the transmission. Don't put any grease on the final drive end of the drive shaft just yet or you will get it all over everything.
Making sure that the swingarm is parallel to the ground, insert the drive shaft into the swingarm until it contacts the back of the transmission. Jockey it around until the drive shaft is engaged into the transmission splines. Once the teeth are engaged, push it until you feel the resistance against the circlip. Now push the drive shaft hard with the heal of your hand to engage it. You should feel it engage and it will not pull back out with normal hand and finger tugs. Now load up the rear drive shaft spline with grease, liberally coating it and making sure that you fill in the valleys of the spline. Likewise grease the splines of the rear drive. As before this is easier if someone holds the rear drive with the speedometer cable opening up and slowly turns the disk rotor while you grease the splines.
Push the rear drive into the drive shaft until it mates with the swingarm. Align the bolt holes, insert the four bolts, and tighten them finger tight. With your handy-dandy torque wrench tighten the bolts to spec. (We didn't have a torque wrench or the specs, so we tightened them "real tight" and Tony torqued them later.)
Un-bungie the brake caliper and place the caliper over the brake disk (rotor). Before you tighten down the caliper, make sure that the clip for the final drive speedometer cable is on the front caliper bolt, and stick the shim for the ABS sensor between the sensor and the toothed ABS gear/rotor on the final drive. Tighten down the caliper, making sure the proper clearance is maintained.
Put the wires back in the holders on the swingarm and caliper. Put a small amount of grease on the O-ring for the speedometer sensor to help slide it into place. Push the speedometer sensor back into the hole in the final drive and fasten it with the allen bolt removed previously. Wipe the brake rotor with a mineral spirits or brake cleaner and clean cloth to remove any grease or junk that may have accumulated on them. Install the foot peg mount and bag mount, making sure that the ground wire for the right ABS modulator is in place before the foot peg bracket is put back on. Also make sure that the little spring for the foot brake lever has not been lost and is in its proper place. Tighten everything down.
Put the wheel back on, making sure the spacer is still attached, put the lug bolts back in, and tighten them down to 77 foot pounds. Put the hub cap (if you have one) back on. Note that the hubcap has a detent that orients it to fit on only one way. Re-install the rear fender and attach the license plate.
You have just finished your first rear spline lube. Congratulations.
Time approximately an hour and a half.
Notes from a spline lube of Tony's '92 K75S on 4-3-94
Standard disclaimer applies.