Chain drive transfer case loud jarring clunk?

[Cariboo4x4]

This question may apply to all chain driven transfer case with planetary gears on main shaft. This manual shift gm nvg261 has these problems. Im pretty sure its not auto transmission or differentials. In park on a hill it would roll in 2H and 4H. It will only hold in 4 low and will only move forward in 4 low. With brake on in drive in 4 low there is a jarring loud clunk felt heard under drivers\passenger seat. When in drive in 4 low Id hear a repetitive light clunk. Buddy was going down hill on highway and truck felt like it drove over a brick so he pulled over. He trailered truck to me. I am trying to get my head around how a chain driven manual shift tcase works with the planetary gear set up for 4low. I understand how my high low on works in a gear driven setup in my tractor or gear driven tcase. There is two forks I believe in this tcase. Im thinking chain is stretched and/or planetary gear broken jammed up somehow. I had a chain skip before yet it skipped in 4 low and 4h yet this tcase has no drive in 2H or 4H. I got as far as taking transfer case out and on Friday had it on bench yet had to end my day. I researched how to remove clip on bearing to split case completely. Its a learning process for me and not sure what to expect to see in tcase for damage if any. A broken differential tooth could cause a repetitive nouse yet it would only move so far if truck was in park. I have too much free time this weekend to overthink it lol.
 

[Tom in Mo.]

Sounds like it's time to split it and have a look. I don't have personal experience on that one but it can't hurt to look inside.
 

[chuck machinist]

[Cariboo4x4]

[DoubleO7]

Might want to put a new chain in the T-case while open.
 

[Tom in Mo.]

A story regarding pinholes. I had a 2002 Ford Diesel that had a clunking rear diff when turning (positrac). Turns out all the gear oil leaked out thru the diff cover pinholes. Saved the differential just in time. THEN I noticed oil all over the bottom of the engine oil pan. Same problem, pin holes seeping oil.
Whoever supplied Ford with those metal pans/covers used crappy steel.