Outer Limits 4x4 Board

I have just had my front ARB diff-lock [rd110] installed and it is fantastic......but I have one small problem.
When I select 4H only my front wheels drive and not the back. To double check this I jacked up one front wheel only...selected 4H and the raised front wheel began spining with no drive to the rear wheels.
4Hcl and 4Lcl workes perfectly but not 4H....I never thought this was possible, Any help would be apreciated...The rd110 was installed by a 4x4 mechanic and he cant explain why.

Hey Rob,
Have you got manual hubs on the front? Maybe they have not been reassembled correctly. When I select 4H and I've forgoten to lock in the front hubs, the cars moves forward but feels like the clutch is slipping real bad. Nothing to worry about though, it's just the centre diff unlocked and sending all the power to the front wheels. Scared the crap out of me the first time I did it though. The centre diff is just trying to send the power to the wheels it sense's are slipping.

Hope this leads to a cure.

Thanks Greggo for the input but I dont have freewheeling hubs , not yet but they will be on very soon......I just cant see how drive can get to the front wheels and not the back ones... ...It seems impossible but that is what is happining

Greggo has answered your question, the centre diff is allowing slippage under load and taking the easiest path with the power, in this case the wheels raised off the deck.
J Top

Thanks fellows,..... it took a little while for the penney to drop....
That was the first time I had experienced this in 4H and took a while to realise that the centre diff was open not locked.