I'm about to put the shaft back. I already lubed the transmission output and shaft splines, but do I need to lube (grease) the u-joint too?  If so, then how do you apply the grease to the u-joint? 

You cant they are a throw away item. The joint can be replaced but it ain't easy.

RicK G wrote:You cant they are a throw away item.

Are you saying that as long as the u-joint is not damaged, then you don't need to grease it and just install the shaft back in.  Otherwise, you will need to replace the whole shaft since the u-joint cannot be removed.

Yep that's right if it feels good keep it, there is no way new grease can get in there.
The uni joint can be replaced if you are lucky enough to find the right replacement but it is a job for experts with expensive tools.

Yes, the U-Joint is a throwaway.  A couple years ago I priced out replacing one on a friend's K100 shaft.  While the joint was something like $27, the machine shop labor to replace it was about the price of a brand new drive shaft with brand new splines.

From what I've seen hanging around here and some other K bike sites, the joint isn't the weak point in the drive shaft.  Almost all failures of Monolever shafts is in the splines at the final drive.

Paralever shafts have had a few joint failures which I suspect are the result of not having the joints phased correctly.  Incorrect phasing puts a lot of stress on the joints.  Another possible failure cause is not having the the shaft locked in the correct position on the transmission output shaft.  It's really tough on the u-joint when it isn't aligned with the swing arm pivot point.

I've had a few uj joint fails over the years. Some would be due to the extra loading caused by the sidecar. Spline failures are definitely more common. I'm pretty sure that there are a few businesses doing an exchange service now if you have a shaft that's worth saving.

The first UJ failure I had was in Jan '93 on a '91 model R100GS (approx 70,000km). The bike had already had a 5th gear/cluster gear failure at around 60,000km, making me and the dog hitch hike from Glendambo to Adelaide and then fly home to Sydney from there (and $$$$ repair cause it all happened just out of warranty). Once I found that the UJ knocking under load could only be rectified by replacing the driveshaft at the cost of $1000, I instantly went to a Yamaha shop and traded the heap of shit on a TDM850, one of the best decisions I ever made. The rear shock failed completely in that time period too. When the shaft failed it was just the last straw for me.

I really liked the R100GS except for the legendary BMW reliability that didn't seem to be installed on this bike.

Al