Shift to 4wd while driving?

[M3 WRATH]

Is there a recommended top speed at which you you can shift from 2wd to 4wd or back again?  Also, provided the road conditions are ok for driving in 4H, how fast can you go?  I was feeling some vibrations at 55 and wasn't sure if that was too fast (smooth packed snow, not dry pavement).  We got our first big snow of the season in Montana and I live out of town so there is a fair amount of shifting from 2 to 4 and back to 2 depending on the condition of the roads I take.  Thanks for helping out!

[Irish_Alley]

what transfer case you have and hubs? i know if i have to have it in 4x4 i keep it there i took it out into 4x2 almost lost her one time lol. so i would take the loss of mpg vs the risk of crashing

[Cody1018]

I have a piece of paper in my truck that has all this information in it. Ill see if i can find it. And if i remember right it says they recommend that you do 45mph max when in 4x4. When you shift into 4x4 i think they recommend no faster than 25. Not sure about your truck but i have to shift into 2wd then back up until they disengage.

[Irish_Alley]

I wouldn't even try it with auto hubs. Only manual since everything is all ready turning

[M3 WRATH]

Good question on the transfer case- I have no idea.  It has C-15085 NP stamped on it but I'm not sure if that even means anything.  It's an '83 with a 350 but transmission was changed to a 700r4.  I have manual hubs which I currently have locked so I can shift into 4H when I need to but I wasn't sure if I need to continue coming to a stop before shifting.  I'm scared to try it while rolling in case something breaks.

[Grim 82]

If it has an aluminum case it's an NP208. I put mine in 4HI while rolling 10mph or less quite often with no problem, and I have gone 40mph for miles in 4HI without a problem. If you do something wrong, it will usually let you know without doing alot of permanent damage.

[M3 WRATH]

Thanks Grim - it's good to see a fellow N. Dakotan here - I grew up in G.F.

[Irish_Alley]

If its all lock and you do go from 2 wd to 4wd everything would be turning at the same speed so it should just go into gear if the conditions of the road are bad enough for 4wd then I wouldn't go over 45 anyway