clunking noise in 4x4

[maddog23]

recently when I put my 1992 explorer in 4x4 it makes a clunking sound every couple of seconds. When I'm travelling at highway speed (100K.K.M or 60M.P.H)
there is a clunkng noise about every seven seconds coming from underneath and a hammering on the floor, like a rock hitting it really hard.
I took it in for service and they replaced the u-joints on the front drive shaft, but it still does the same thing.It only does this in 4x4. Can anyone help me as to what to look for next. thank you for your time.

 

[Rustang©]

first of all, going 60 in 4x4 mode isnt a very good idea, for safety, or fuel efficiency!

on to your noise, sounds like your shift motor might be giving you issue or possibly you hubs. Have you replaces your autos with manuals?

 

[maddog23]

is it possible that the motor for the 4x4 is not turning the shaft far enough and that the clunking noise is coming from the diff only being half way engaged?