Experiencing diff and visco problems on RRC after mounting big rear tyres

[Beaubien]

To give my Range Rover 3.9 (1992) a better look I exchanged the rear tyres for bigger ones. Big mistake! After only 1 km my car slowed down, forced me to the right and stopped. After 30 seconds I drove away again but after 1 km the same happened. Again I paused 30 seconds and returned to the workshop, slowly. Then there was a bang coming from behind and after that the car drove 'normally'.
Back in the workshop I remounted the original tyres. Driving on the highway (above 80 km/h) I hear a whine in the rear and feel vibrations.

I did the following checks: my tyres are all the same size now, I jacked up the left front wheel, I can turn it, the wheel doesn't lock, no stress there. According to articles on the internet this would mean my visco-coupler isn't locked.

I guess this is what happened, during the ride when I had the false tyres mounted: The visco did stiffen up, causing the transmission to wind up and bringing the car to a full stop. During my 30 seconds pause the visco cooled down and unlocked, giving me way for my second attempt with the same result. When driving away after the second 30 seconds pause something must got damaged, causing the bang.

My question is: What is the cause of the bang? Is my front diff and/or rear diff damaged? And will my visco still be working properly, although it does not seem permanently locked?
I'm looking forward to your ideas and suggestions!

 

[alexandermeerkat]

if you raise any one wheel it should be almost impossible to turn the wheel by hand. when for example a front wheel is raised you should just be able to make the front prop turn with a self gripping wrench like a stilson. this would be the viscous coupling working ok. if no resistance or total resistance the viscous is suspect. if you read the rave manual the test procedure is in there. the most likely is you have stripped a halfshaft spline or shattered a planet wheel in the diff. pull the halfshafts and drop both diffs and have a look., not a very big job. in an extreme case you may have broke the viscous and splines etc inside the transfer box. rule the axles out first.

please pm me if you need more advice.