Graeme, trying to distill your post. Is your dislike of DCs due to:
1) the extra weight making DC joints more prone to failure, or
2) the quality of workmanship/parts on DC joints available for Rovers making these DC joints more prone to failure, or
3) the extra weight making catastrophic damage more likely in the event of failure?
DCs are run from the factory on some vehicles so it seems like there must be a way to make them reasonably reliable? Greasing every 250 miles seems very excessive. And, would a DC really be less reliable than a standard joint bring run well beyond its max angles?
I'll check out Drive Line Services. I also saw a place on yelp in San Jose, I think it was South Bay Drive Line, that has great reviews. Probably will talk to both and see who I like best.
All of the above, in the order 1, 3, 2. And also they are not necessary for the majority of Rover builds. A double cardon naturally has greater play due to the centering arrangement to ensure that both joints move equally. Some don't have a grease point for that center ball, and those that do are really hard to ensure grease actually gets in there. Once that wears, the whole thing is out of balance, and basically shakes itself apart with high frequency vibration (the two out-of-phase joints cause higher harmonics). If you measure what you need for almost any Rover, it is way within what a single joint can do. You never get to the 25 degrees that a standard single joint can do, and with 30 degree GKN "ultra" joints can allow, double joints are unnecessary. Personally. I like the GKN joints and will pay extra for them. Never had one fail that wasn't abused. "Abused?" Yes, 40,000 miles of road and wheeling, without greasing, on a 2" lifted Classic. I recently threw away the evidence (the spider looked like it had been welded it had got so hot).
250 mile greasing interval might be excessive, but 250 becomes 500, becomes 1000 .... and then the next thing you know things go bang. We're lucky in California that we don't have water and salt, but for 5 minutes under a vehicle, I'll er on the side of caution. Changing a gearbox is the worst job on a Rover, in my opinion.
DCs are rarely fitted on standard vehicles for flex reasons, it is for vibration reasons. This is why the D2 has one and the D1/RRC/Defender doesn't. By clocking the UJs most harmonics can be designed out, and adding weight to stop pinion vibration can help too (but how many of us still have those fitted?).
South Bay Driveline are great, if you catch them on a good day. Steve knows what he is doing, but their prices are usually rather high.
A good driveshaft is usually painted blue (!!!). Not all drivelines are built equally.
Note in this picture the position of the involute splines. Far better when off-roading.
Edited by GraemeWare, 26 December 2015 - 10:20 AM.
Graeme Ware -- San Carlos, CA
1990 Range Rover Classic - LT230 Transfer box, Warn winch, 2" lift, 235/85-16 Dunlop MUD Rovers, "Blue Submarine"
1996 Discovery 1 (R380 Manual Transmission, Ashcroft under-drive, RoverWare rear bumper, 33x12.5-15 BFG ATs) -- we call her "Katrina" -- Fordyce 7.5 mile survivor
1999 Discovery 2 (D1 CDL Linkage, 265/75-16 BFG A/T KO, RoverWare front and rear bumper)
1993 Jaguar XJS convertible; 1971 Triumph GT6; 1959 Morris Minor convertible
other assorted British pot metal ...