Dual cardan or constant velocity (CV) joints are often used on off road vehicles that have been raised for ground clearance and there is just no way to align the drive shaft properly.
I was having driveline vibration with my 2-piece shaft, I took it apart and found the front U joint had longitudinal grooves where the needle bearings were sliding back and forth rather than rotating around the cross trunnion – known as “brinelling”. I noted in previous posts that my engine/trans is cocked slightly to the right which I believe was the cause of the excessive wear.
Using a CV joint greatly reduces the requirements for aligning and phasing of the driveshaft. A U-joint operating at an angle actually rotates in an ellipse, you must have a second u-joint operating at the opposite angle to cancel out the induced vibration. A CV joint is actually just two U-joints mounted together with linkage to keep the angles equal.
I made the switch mainly because I was tired of fooling around with the two piece shaft and it just happened that the Pick ‘ur Part yard was having a half price sale, so I got the complete Lincoln shaft for $15. I figured that it was worth it to experiment.

Try these links
http://www2.dana.com/pdf/J3311-1-HVTSS.PDF (this one is great!)

http://www.dana.com/Automotive_Systems/Driveline/

http://www.arizonadrivelines.com/cv_parts_(double_cardan_type).htm

http://www.4crawler.com/4x4/CheapTricks/Driveline-101.shtml

http://www.4xshaft.com/

http://www.discoweb.org/shafts/tomwdriveshaft.html

TR Conn
282C 5.0L AOD