My 1993 R100GSPD, Rocinante, has taken me to school on this issue. About 20 months ago, while preparing to ride to Alaska and Prudhoe Bay with my brother & my nephew (my greatest ride EVER), I swapped the driveshaft with one that had fresh u-joints. I pulled the still seemingly good driveshaft out of bike when I installed the rebuilt unit. The bearings on the old shaft's u-joint felt nice and tight. I made it through the last two summers and one winter without problems on the rebuilt shaft. A few weeks ago, the bike had that "clunk," and I pulled the driveshaft out. The front u-joint had shed it's bearings. I inspected my old driveshaft and the one I had just taken out of the bike. I put them each in a vise and checked to see if the the front and rear u-joints were "in phase," meaning that the u-joint's "U's" that are fastened to the shaft body/rubber damper assembly, are parallel. I put small straight-edged rulers on these pieces and a visual inspection showed BOTH shafts had their u-joints about 7 degrees out of phase. CONSTANT VELOCITY (CV) joints have their input & output sides running at a constant velocity with each other regardless of angle (thus the name). Airheads tech guru Oak Okleshen, was working on a CV joint retrofit for the early paralevers, but development costs (and perhaps projected product liability costs?) have indefinately stalled this. Understandable, considering how small of a market for such a conversion would be. U-JOINTS, with constant-speed inputs, have small accelerations/deaccelerations when you run them anywhere except at zero angle, and those accelerations/deaccelerations increase as you increase the angle of the bend. Unlike the driveline u-joints you find on rear wheel drive cars, the Airhead Paralever u-joints run at a rather extreme angle, thus greater accelerations/deaccelerations. Having the u-joints in phase, or in alignment, minimizes the affects of these accelerations/deaccelerations. Likewise, an out-of-phase shaft has the u-joints "fighting" each other, and beating that poor rubber damper like a red-headed stepchild with each rotation. The natural rubber damper in the driveshaft between the out-of-phase u-joints breaks down from the added stress and the shaft twists even more, pulling it more out of phase, which adds more of the hammering stress, which then pulls it even more out of phase...a cascade effect, mind you. I am now of the belief that simply replacing the u-joint bearings and not addressing the phase issue is throwing good money after bad. OPTIONS: ANOTHER BIKE--and lose the otherwise owner-friendly panache of this wonderful airhead. An giving up Barley Therapy. :eek1 NEW BMW DRIVESHAFT--expensive, but will give you a servicable life for, what, 20,000 to 40,000 miles? At this point, a chain drive begins to sound real good, validating the first option. SOLID SHAFT--but if the miserly BMW bean counters at the time were willing to risk catastrophic transmission failure by leaving out that lousy $.85 circlip, how could they justify the expensive, rubber-dampened driveshaft assemblage if a simple piece of metal rod would work in its place? That rubber damper has a purpose, perhaps to protect the final drive or transmission. Heck, my Honda CL90 has a rubber "cush hub" between the rear sprocket and the hub to protect the driveline from the titanic forces that wee thumper, no doubt, unleashes. We're dealing with about 10 times the power with the Airhead driveline from the 90. I am skeptical of the long range utility of the solid-shaft solution. Anybody have any real information, data or experience on this? REPLACE THE DAMPER--this is the solution I am pursuing. Guy Henderson (209-962-7500 firstname.lastname@example.org) pulls out the worn natural rubber piece and replaces it with one made of urethane rubber of the same durometer, which, according to Guy, should stay in phase about 3 times longer than the stock, perhaps 90,000 miles? Cost, currently, is $175, for this urethane piece installed. He has more info in the advrider vendor forum. Link: http://www.advrider.com/forums/showthread.php?t=130764&highlight=driveshaft+confusion It doesn't hurt that Guy is an Airhead GSPD AND an Indian rider (a fellow after my own heart!). Thoughts, fellow Airhead GS'ers?