I came across your web page of rear steering bikes and have studied it with great interest. I have a Thebis and I freely admit that all of your comments regarding its complexity, fragility and lack of stability at even moderate speeds are, unfortunately, dead on. That said, there is something about them that appeals to anyone interested in the technology of recumbents; almost like a failed but noble experiment in flawed design.
Presently my Thebis is ripped apart waiting for new hub bearings for the rear axle. Judging from the few emails displayed on the net about Thebises (Thebi?), I gather that most people give up on them when the universal joints break. These joints were built by a company called Lovejoy specially to order for the bike. What I discovered when I looked into replacing a broken joint on my bike was that Lovejoy is still in business, and still makes small universal joints. I was able to upgrade to a slightly heavier, more durable size without having to modify the chassis of the bike. The original assembly featured hollow, heat treated shafts fixed to the joints, all non-standard and all devilishly expensive to fabricate, assuming you can even find someone willing to take the job on. A solid shaft can be substituted and welded on the replacement universal joint, with a weight gain of only a few ounces, and much lower fabrication costs. The extra strength of the solid shafts vs. the hollow ones lets you get away without the heat treating. I did the universal joints on both sides of my Thebis at a general machine shop in Toronto for under $300.00 (CDN), parts and labour, and they are much more robust than the originals. Seeing as these bikes were astronomically expensive new (I've heard somewhere over $3500.00) it seemed a reasonable price for getting this deathtrap...er...bike back on the road. The trick, as near as I can tell, for keeping these universal joints intact is to take special care with the adjustable stops on the steering gear. This will keep the joints from exceeding their designed maximum angle during use. If you push these joints past said angle, they will start "eating" themselves quite rapidly. The clicking noise that you will hear when you are riding is the joint self-destructing. Each click is a tiny bit of metal being sheered off, discreetly hidden from view under those little rubber dust boots.
As any Thebis owner knows, George Perkins, the original manufacturer, is long gone. I did manage to get hold of one his sons a few years ago out in British Columbia, but the old email address and phone number that I have are no longer in service, and I have been so far unable to track them down again. They were still apparently designing and building prototypes, with a land speed record attempt in the cards, but were of absolutely no help in supplying parts or information. This means that Thebis repairs are strictly a do-it-yourself proposition. I have yet to find a bike shop that will even seriously look at one, and I live in a metropolitan area of over 3 million people. If you should happen to come across anyone needing information regarding Thebis repairs, please feel free to pass my email address along to them.
Best Regards, Paul Jarvis.