Although the BMW K and R series rear drive is considered to be low-maintenance, it is not maintenance-free. As I have found out for myself the grease in the area of the rear gearing (length compensation) had become too thick over the years, "volatilized" and the gearing was as good as "dry."
In my case the rear drive was disassembled to give it a fresh 2K lacquer painting. It´s simply easier to paint the parts when disassembled.
Here´s the today´s ingredients. You´re good re-using all screws, just replacing all seals (Shaft sealing ring, O-ring etc.) is a must.
We start the journey putting the crown wheel in again. It´s crucial heating up the cover plus crown wheel to 80 degrees celcius. If the crown wheel does not slip in on its own, the parts are not warm enough. Never try hammering the wheel in!!!! You´ll have a hard time if this gets canted in side the housing. Also make sure all parts are cleaned and dust free, especially the distance rings.
Next stop shaft sealing ring. Please make sure the cover has cooled down to a reasonable temperature again. This will make sure the crown wheel sits tightly inside the housing again. You´re good adding some grease (inside and outside) to the sealing ring.
This time we truly need a hammer. You can use a BMW special tool hammering the new seal in, but a cheap DN 100 sewage pipe (no joke) from a tool market also does the job. This pipe has the exact same diameter as the seal and won´t damage the seal when hammering on it.
Job done. Make sure the seal does not stand above the housing. Next thing to check is the correct fitting of both gears. Check the contact pattern between ring gear and drive bevel gear.
I´m using white chalk here to to mark the teeth as it´s easy to clean afterwards. Then, put together the whole rear drive first time and turn the wheel around.
Put off the cover again and in an ideal case, the contact pattern looks like this. Exactly in the middle of the drive bevel. If that´s not the case the whole drive needs to disassmbled again and both gears need to be distanced.
We´re now good closing the drive. Don´t forget the O-ring between housing and cover and also put some grease on it. Again, we´re gently heating up the cover to 80 degrees. Check the temperature from time to time not to damage the new seals!
Torque all 8 screws crosswise to exactly 21 NM+2. Enjoy your new rear drive. :-)