Stock 91 w250 4x4, locking hubs. Its not the u joints or the front shaft but Im getting a clunking from the front with forward motion. it's really bad when I try to engage four wheel but also does it sporadically with the hubs free and in 2Hi range.I think the cold gear oil still turns the front diff enough to create the clunking, so I am thinking front diff. It's never been apart and its plowed enough snow to cover Mt. Everest!! Is there a particular part in the diff I should focus on? Or am I way off base here?

 

i had a mystery clunk and it was worn/missing sway bar bushings.

 

look for cab mounts core support mounts u bolts worn sping bushings even a trans mount can transfer a clunk

 

Just a though, but on my truck, either the brake slides are worn on the front calipers, or the slides were worn on the knuckle. The brake calipers would move forward a little whenever I touched the brakes after using reverse or rolling backwards. Just a thought. To fix it I added material to the leaf spring-like object between the bottom slide and the caliper. Clunk gone. Crawl under there and make sure the calipers are tight in the slides.

 

Thanks for the ideas , I will look at them all.

D-Ram