When driving on the beach 4wd hi was clunking and appeared to disengage without notice. 4wd low would do it but not nearly as often. Clunking may or may not have indicated when it went out and when it went back in. When in 4wd hi, clunking was every 1/2 mile or so at about 15mph but was irregular. Felt like it was coming from under front drivers seat, (around the transfer case). Truck has 170,000 and had no other problems. Any suggestions.

 

What year truck? Electronic of manual 4wd?

 

1997 xlt supercab, 4.6, automatic transmission, Manual 4wd shifter on floor