Problem with Transfer Case or Hubs?

[1985LWB]

When running in 4WD, high or low, I get a clunk that is strong enough to be felt at low speeds. I have heard and felt this before on a Ford F-250 I used to run, when you would accidently try to drive on pavement in 4WD. The wind-up and then, BANG, as the whole thing lets loose when you finally get some tire slip. In the NB, it happens on a regular interval, almost like, it takes some many revolutions to wind-up and then, BANG, it lets loose. It will do it more under power and hardly at all when coasting. It will do it it forward or reverse. I have deduced that we are either having hubs letting loose, or a stretched chain in the transfer case.

How much engagement should the auto hubs have when they are engaged? 1/4 spline, 1/2 spline, full spline length, etc?

I only have a Haynes manual, which does not have a diagram of the transfer case. Is there anywhere online, where I can find a diagram or which manual or manuals should I pick-up to get the information I need.

I do not run the NB in 4WD on pavement, I know better, having learned the hard way many years ago. It is "clunking" even on a loose gravel drive, tracking straight ahead.

Thanks