Fiat Ducato 159" wheelbase Dangel 4x4 - convoluted driveline curiosity

A big old tired yellow bus. But he does have 4x4 lurking under that low, long body. Here is a brief dynamic of the underneath of a Dangel 4x4 version of Ducato.
Standard vehicle is front wheel drive. Retrofitted rear wheel mechanical driveline must negotiate two times 90deg transfer boxes and a vicous coupling until the rear side-entry differential to the rear wheels.
Here we had the van on the lift in the garage trying to diagnose the cause of binding/knocking behaviour experienced at low speed with high steering lock. We are suspicious if the viscous coupling might not be somehow permanently engaged. We did kind of expect all the wheels to be spinning up under engine idle, but were surprised to see one of the rear wheels not moving, so all of the rear drive being lost to one side. Of course there is no diff lock.
Also unclear if it is a fair test or not diagnostic to judge this behaviour on the lift where there is no resistance being applied to the driveline so that perhaps only small insignificant friction imbalance between the drive paths to each wheel is enough to give the odd appearance of a wrong function.
Nonetheless, it gives an obvious visual of the amount of whirring and spinning of shafts which are for 99% of highway driving contributing no added traction only drag on the engine. We reckon there is about a +1 to 1.5litre/100km penalty on fuel (10-15%), but have not been able to make any conclusive test on that. It seems a neat idea to disconnect the rear drive and make some scientific back to back. The vehicle is very sluggish to drive by comparison with a standard 2wd-fwd. With so little ground clearance available from the 15" wheels and 215/70 R15 tyres fitted on this vehicle, combined with the long wheelbase, the owner has not ventured off the street to test his luck 'off-road'. So we honestly can not attest to what the capability could be.

[@yasinergul]

Solved?

[@pampalini1313]

I have a Fiat Ducato with Danger drive and the same symptoms but no one can tell me what the cause is. Do you already know or could you write to me? Janusz

[@johncampbell4498]

Hello, sorry for late reply. Quick answer - is to go an read the deatiled work of Visco-Kern, Austrian guy - vw-kern.at/visco_en.php Unfotrtunately i found no one who has made similar deep dive into the specific problems of the Dangle Visco coupler, but i think you might find that it is the same or very similart c omponent as used in the first gen Land Rover Freelanders, the Freelanders also have similar troubles with their viscous couplers. The Dangel Ducato vehicle featured in my video was showing some severe problem with the transmission binding during tight steering driving, this is a clear sign of the visco coupling starting to 'harden' and becomes always partially or fully engaged and so when driving in tight turning radius the rear wheels speed is fighting with the front axles speeds, and this will cause big wear on the pto and the main gearbox. For the vehicle in my video, it belonged to a friend of mine who had bought this Dangel at same time as i had bought one, but i returned my Dangel directly when i realised the potential cost of repair on mine i had immediately a rear transmission leak the day after i bought it so i was able to return it dirtectly and subsequently brought me the idea for my project of adding an electric on-demand rear drive system.