1998 f150 v8 engine. When the vehicle is put in 4 wheel drive and when you steer it it clunks like something is hitting steel on steel.Only in 4 wheel drive. Comes from the left side of the vehicle when turning left or right .Most pronounced when turning but can be slightly heard in straight line. Gradually has been getting worse over 3 months. Sounds like the front diff.

any help would be appreciated.

Thanks
Mike

I had the same problem, and I found a heat shield rubbing against the front axle. Removed the shield, and the klunk went away.

My guess would be your front U-joints are toast.