OK, big Harleys (like my 04 Road King) have the swing arm pivot bolt attached to the frame like almost every other motorcycle. But, Harley used rubber bushings to give it the plush ride. Nice ride, but it also means the rear swing arm can get deflected, creating a nice wallowing wiggle in turns some times.
As is typical of motorcycles, the rear of the transmission/engine is hung on that bolt. It works. The swing arm has two bearings out at the ends, and the engine/transmission sits in the middle in between these points.
Now this is where things get weird.
The "fix" everyone uses for this wallowing wiggle isn't to use stiffer bushings where the swing arm bolt mounts to the frame, but is to use a turnbuckle to lock the rear of the transmission to the frame. The claim is that by preventing the transmission from moving side to side, you effectively lock the sway arm in place and eliminate the wobbling.
To me, this seems like placing the cart before the horse. Especially since the only way I can see this working is by having the swing arm grinding against the transmission case. The transmission was never intended to hold the swing arm in place. Not saying this doesn't work, it seems it does. Just that it seems like a darn poor way to do it. Especially since the only way I can see it working is to have the swingarm grinding against the side of the transmission case.
Ask about this on a Harley forum or two, and about all you'll get is that Buel did something like this (he did) and Harley used a setup like this on the Sportster (they did), therefore it's a perfect fix. But it manages to fail to notice that in these two cases, the swing arm really is mounted onto the transmission, and not the frame (interesting design btw). In that case, everything is made to do this job, complete with bearings and such.
Some of you folk are Harley nuts and motorheads. Maybe you could explain to me why these transmission to frame turnbuckles really are a better "fix" than stiffening the rubber frame bushings of the swing arm pivot bolt?