'89 gmc sierra 2500 transfer case issue?

[ninepoundhammer]

Hey guys, i had a hand-me down '89 2500 sierra passed down to me last winter, and i've since been slowly working on simple maintenance with it. Learning my way around a sbc 350, body work, etc. (This is strictly a farm truck.) This afternoon, i was testing the transfer case again because i had noticed a slight.. almost like a groan, when i would shift from 2wd, through neutral and into 4Lo last sunday.I allowed the truck to warm up this afternoon, typically around 90°C on the gauge. I shifted into 4Hi,(floor shifter, not push button) and began working my way through the field on our property. As i was making my way back into the driveway from the field, i stopped and shifted into 4Lo, and there was a slight grinding noise as it shifted, but no other issues. As i began making my way into the driveway, the transfer dissengaged, then re-engaged itself 3-4 times. I could clearly feel it dissengage and re engage, because it is snowy here and the ass end would kick out, then when it re engaged, the truck straightened out. There was also a lurching when this happened. I pulled up to where i park the truck, and when i went to shift out of 4Lo, there was a grinding noise similar to when the clutch brake was shot in my dad's mack, and just continuously grinds until it slows enough to shift. (Closest relation i can make to the noise) i attempted to shift out of 4Lo 3 times, the third time ignoring the grinding and forcing it into neutral. The grinding stopped, but as i shifted into 2wd, it occured again. I also have been noticing a burning smell the last few times i've used the transfer case. Smells the same as after a burnout. ATF is full, differential is getting checked tomorrow morning, but does anyone have any idea what might be happening? I checked for leaks of any kind, and found nothing. Nothing out of the ordinary. Shifting into 4Hi has never been an issue, just 4Lo. Any help is greatly appreciated! I can try getting a video of the grinding tomorrow if anyone wants to take a wild guess based on the audio

[ThatOneGuy]

Usually you need to put the truck in Neutral on the gear selector and then select 4Hi or 4Lo and then put the vehicle in Drive. There are many reasons why it's grinding but the best way would more than likely take the transfer case out and pull it apart and take a look inside.

[LMB]

Something is worn out, GM is shift on the fly up to 40moh for the 2wd-4hi shift on those old ones (owner's manual for my 92 of the same body style and basic powertrain states so)

Someone may have missed a shift from 4hi to 2wd and missed 2hi, through neutral and into 4lo at one point.

[James60470]

Almost anything with 4x4 is able to be shifted into 4hi while moving. It's only when you shift into 4lo that you need to stop. Especially with an automatic. An automatic needs to be placed in neutral before you can make the shift into 4lo, and back into 4hi.

[LMB]

Doesn't mean someone didn't something stupid at one point.

[ninepoundhammer]

Thanks guys, i knew about shifting to neutral but i never did figure it out. The frame snapped a couple months after i posted the thread. I've since been extremely slow at pulling the motor, but the issue never went away. I was told when i got the truck that there was work done to the 4wd shift linkage, my guess is it screwed up again and caused it to grind.