Land Rover Repair: Series 3 - 4 wheel drive, freewheel hubs, inclines

Question
My series 3 does not appear to be engaging 4 wheel drive. What checks can I carry out to be certain? I'm unable to ascend slippery inclines either with 4 wheel engaged (the mechanism operates corectly) or in low ratio, which automatically selects 4 wheel drive. However if I reverse up the incline in 4 wheel drive I don't seem to have a problem. My tyres are good. I have freewheel hubs, which appear to be working and are engaged. Is the problem likely to be in the transfer box. I've not heard any nasty noises. Grateful for any help you can give

David  

Answer
Jack up the front end with a rolling type jack under the differential.  Spin the front wheels - when you spin one side the other should rotate the other way.  Put the vehicle in low with the hubs locks and see if it drives forward with the front wheels off the ground.  If it does, repeat with the back wheels off the ground instead.  Spin the back wheels, too.  If it moves both ways all 4 wheels are getting drive.