Loose tail on my 94 R1100RS

[ANDYVH]

By loose tail, I mean the entire tail section. I can move it up about 1/2" very easily by lifting on the tail rack. Almost seems to "pivot" up on the rear subframe tubes going to the back, which support the tail piece, tail rack, inner fender, rear seat section, etc. Nothing is missing or loose that I can tell so far. The bolts that attach the rear subframe braces to the tranny are in place and tight. The subframe doesn't move at the rear footpeg braces. But, when I hold my pinky against the junction of the footpeg brace tube to the top subframe tube, and lift, I can feel a gap open up there, which is where there should be a solid weld connection.

So the rear panels and tail piece got to come off as I suspect two broken welds back there. The rear of the bike can't drop (yet) because the top of the tube is still intact. But I suspect a crack on the bottom of the tube. Just wonder if anyone else has experienced anything like this on the 93/94 vintage R1100RS. I should also note that my bike has a homemade tail rack to mount a Givi 52L tail box.

 

[PGlaves]

Voni's R1100RS had a weld break on one side of the rear subframe years ago. I removed the subframe and had it welded. It hasn't broken again since then. That was 210,000 miles ago.

 

[bc1100s]

I removed the subframe and had it welded....That was 210,000 miles ago.

Apparently the subframe is a wear item.

 

[PGlaves]

Apparently the subframe is a wear item.

I have seen fractured subframes on numerous BMW motorcycles. Most - but not all - have been caused by exceeding the rather miniscule weight restrictions/recommendations BMW specifies for tail trunks and side bags hanging off the subframes.

I would venture the guess that at least 75% of the BMWs arriving at the national rally where the rider is loaded to camp exceed the weight specifications for the luggage - ergo subframe.

 

[MIKEFIGIELSKI]

By loose tail, I mean the entire tail section. I can move it up about 1/2" very easily by lifting on the tail rack. Almost seems to "pivot" up on the rear subframe tubes going to the back, which support the tail piece, tail rack, inner fender, rear seat section, etc. Nothing is missing or loose that I can tell so far. The bolts that attach the rear subframe braces to the tranny are in place and tight. The subframe doesn't move at the rear footpeg braces. But, when I hold my pinky against the junction of the footpeg brace tube to the top subframe tube, and lift, I can feel a gap open up there, which is where there should be a solid weld connection.

So the rear panels and tail piece got to come off as I suspect two broken welds back there. The rear of the bike can't drop (yet) because the top of the tube is still intact. But I suspect a crack on the bottom of the tube. Just wonder if anyone else has experienced anything like this on the 93/94 vintage R1100RS. I should also note that my bike has a homemade tail rack to mount a Givi 52L tail box.

This is a known issue with early model R1100RS bikes. BMW updated the rear subframe in 1995 to address this issue. There is a stronger version with welded in gussets. You can weld and gusset yours or install the newer version. We have one available used here: http://www.beemerboneyard.com/46512320698.html
Hope this helps,
Mike

 

[ANDYVH]

Well, so far after taking apart the tail end of my 94 RS, I found what I suspected. Each rear subframe extension, the stubs that extend back past the triangulation of the frame tubes, had cracked through from the bottom up. When loaded, like carrying a load or passenger, the tube stubs are pushed down and tension is increased on the upper half of the tube. A tube in tension does ok. But, any bump would cause the back end of the bike, fender, taillight housing, tailrack, rear seat, my passenger, tailbox, to bounce up slightly, and bend the cracked tubes up.

You bend coat hanger wire enough times. it'll crack, just like the stub extensions, right behind the triangulated tubes. So I brazed those cracks up. Now I am fabricating gusset plates that will span the area from the triangulated tubes back to the mount for the RT style undertail bracket that my RS had because it had the (then) optional tailrack. I also plan to extend that bracket so it reaches up to the gusset plates and I'll bolt into those as well. Should give me plenty more support than it ever had before. Pics to follow.