What kind of fluid did you put in there?
I once drained the Amsoil ATF out of my old truck for routine maintenance (NP231 tcase) and filled it back up with Mobil 1 ATF.
The tcase would not stay in 4HI, once I gave it some gas it would pop right back out. I also 'clunked' hard when trying to engage the lever.
I bought some cheap Mopar ATF+3 (what the tcase called for) and filled it up. I ran the truck in 4WD for about 10 mintes and drained it back out.
I then reinstalled Amsoil ATF and the tcase (to this day) worked great.
Check to make sure what tcase you have and then checn to see what fluid type that specific tcase calls for. I was quoted like $600 for a tcase rebuild and I flushed the tcase myself for $50 and it worked great.
I once drained the Amsoil ATF out of my old truck for routine maintenance (NP231 tcase) and filled it back up with Mobil 1 ATF.
The tcase would not stay in 4HI, once I gave it some gas it would pop right back out. I also 'clunked' hard when trying to engage the lever.
I bought some cheap Mopar ATF+3 (what the tcase called for) and filled it up. I ran the truck in 4WD for about 10 mintes and drained it back out.
I then reinstalled Amsoil ATF and the tcase (to this day) worked great.
Check to make sure what tcase you have and then checn to see what fluid type that specific tcase calls for. I was quoted like $600 for a tcase rebuild and I flushed the tcase myself for $50 and it worked great.