Grating sound from Jackeroo front wheel

I've got minimal knowledge on 4wd's, and a question about a strange clucnking sound coming from the front right wheel of a 1985 Jackaroo fitted with auto hubs. Almost every morning a grating sound builds up from the front right, and won't go away until I brake the car to a standstill. Just as the car stops a loud clunk comes from the wheel, something seems to 'drop into place', and then no more sounds are heard for the rest of the day. The next morning however, the same grating sound starts up.

I've had a few mechanics look at it, but they either can't explain it, or suggest anything ranging from the auto-hubs, to loose brake calipers, to the 4wd transmission, but they don't seem very confident at all in their predications.

Any suggestions or hints out there ??

cheers,

vince