So I rebuilt my NP231 a week ago and noticed an occasional grinding noise when I shift with higher RPM's. Started narrowing it down and I think it's the front fork trying to engage. Tried running it in 4wd and when I do, the sound disappears. The rebuild went perfectly except for the synchronizer sleeve came off at one point. I put it back on but I'm not certain I put in on the correct direction. Two questions...which way should this sleeve had gone back on? If I put it on incorrectly, could that potentially be the source of this issue?

 

Grab the appropriate year service manual from this thread. Dig thru the t-case section, and their should be illustrations showing the orientation of the parts.