why does ther front end clunk when i steer on 4wheel drive when i turn

if you are turning the steering all the way to eather side this is normal,if just regular driveing like in a curve in the road you could have a hub assemely going bad.

im not sure if you have gnk style or u joint style if you live back east thers a lot of rain snow etc when tou turn your weels real sharp if its ujoint they move quite a bit out of the normal rotation and that fealing your geting is called phaseing thats one of the reasons manufactures switched over to the later style for more

smother turns and no binding issues if it the front axels if thers lochers the dont get anny movement and what happens is condinsation builds uo on yhe trunion and berring surface its actuly good to put your truck in 4 hi for a mile or two a mo on dirt to get the greese losened up to keep things working right