Right, I'm back.
Having had a bit of a think I've written out some tests. The first one could be done by Ben and A.N.Other before going to Chris' place.
Here we go:
From what has been written, there is one simple test to identify where the problem lies.
With two people:
Put the transfer box into ‘H’ (centre diff open) and the car into first gear. Now try to drive forward.
There will be no movement and a nasty noise from somewhere.
The second person then has a look under the truck with a torch (BE CAREFUL - don't crawl underneath with it running!).
If the front propshaft is spinning the problem is at the front.
If the rear propshaft is spinning the problem is at the back.
If neither propshaft is moving the problem is in the Transfer Box.
Simples!
If the problem is in the Transfer Box I’m afraid it has to come out to be repaired. It’s likely to need a Centre Differential repair.
If the problem is in an axle we need to determine whether it’s a driveshaft or a differential problem (it could also be stripped splines on a Companion Flange, but I think that’s unlikely).
Front:
Engine off, Gearbox in Neutral and Transfer Box in ‘HL’.
Jack both front wheels off the ground (rear wheels on the ground, handbrake on).
Turn one wheel – the other one should turn in the opposite direction and the front propshaft shouldn’t move. If this happens and it feels ‘normal’ it indicates that the Crownwheel & Pinion have a problem and that the diff pinions are OK(ish). Both driveshafts are working.
If the ‘other’ wheel doesn’t move it indicates that a driveshaft is broken – but which one??
Put the Transfer Box into ‘H’.
Hold one wheel and turn the opposite one – does the propshaft turn??
If No – you are turning the wheel with the broken driveshaft.
If Yes – try holding/turning the opposite wheels.
This should reveal which side the driveshaft is broken.
BUT . . . There is a world of difference between turning something by hand, where broken bits can catch and appear normal, and doing the same thing with 100BHP behind it. Be aware that the truck can fool you so check very carefully and pay attention to ‘feel’.
Chris knows all about replacing driveshafts (I haven’t done that) so I’ll leave it at that.
If it looks as though the Crownwheel & Pinion have stripped the diff will have to come out, which means drawing the driveshafts out and so-on.
Rear:
Just repeat the above tests with the rear wheels off the ground and the front wheels grounded – Handbrake off.
If it looks as though an axle diff has failed, drain the oil and see what comes out – That should prove that you didn’t imagine it!
I’m sure that there are other tests that people will suggest and much will depend on what you find on the day. This should be a reasonable starting point though.
I’ll look forward to hearing the result.
Bob.