GL1200 GOLDWINGS

I'm in a little bit of a quandary here. Ever since I got my 86 back together (it had been in a crash before I got it) I've had a suspension problem and I'm running out of things to investigate. Whenever I hit a moderate size bump it's like the rear end is bottoming out, "thunk", very solid sound and feel. I've raised tire pressures, I've lowered tire pressures, I've raised shock pressures, I've lowered shock pressures. I've checked the swing arm bearings when I had the rear wheel and shocks off. I can raise and lower the rear end with the air shock pressures and they don't leak. I can see no marks on the tire from where it would be hitting. As I say it takes a pretty good bump to make it happen ya know like railroad crossings. The shock bushings aren't great but they aren't gone either. I can't find anything that would be interfering with the swing arm travel. Any ideas? Thoughts? Things to look at? Broken shock? Bad springs? Clogged air line?

if the shocks have never been rebuilt its probably a sign that the fluid has gone bad,the springs are shot and/or the rebound bumper inside with the springs has jelled and as such no longer works

most likely its one or all of the above

Is the only real option replacement? I would hate to go through all the work of a rebuild just to find out that the springs were still shot

with a full rebuild the spings can be replaced,does require building a fixture to completely rebuild the shocks
and replace the sprimgs
http://www.bikebandit.com/progressive-su...d?m=151650

rebuild steps are shown here http://www.goldwingfacts.com/forums/10-r...200+shocks

Thanks, I just found those too! It looks like the only other new part is to replace the oil seal. What about the rebound damper? I have the skills, equipment and ability to fabricate a spring compressor to do this job.