We got 6" of snow last night, which spurs the question, what's the top speed for a '79 Bronco with an NP205 when shifted into 4WD high? I've heard 35mph is the limit on dry roads, but what about in snow?

 

NEVER drive in 4WD on dry roads. You'll destroy your transfer case.
Having the hubs locked is fine, but you must shift out of 4WD into 2WD when you hit dry road (which you can do while moving).

As for top speed while in 4hi, as fast as conditions allow. If you need the extra traction of 4wd, you probably shouldn't be going all that fast. (Always remember that 4wd doesn't help you stop any better.)

 

The manual I had said 55 MPH, as conditions allow of coarse.

 

Is there any trick to shifting 2wd to 4wd while moving? Do I need to be under a certain speed? Do I shift while leaving the transmission in drive?

 

I don't believe so. Mine's a manual, and all I have to do is put the clutch in and move the shifter between the two (2hi -> 4hi and 4hi -> 2hi). I would think with an auto you wouldn't have to do anything.

I think you need to be under 35 to be able to do that, but others may have different opinions. I know I've never had an issue shifting between the two while driving over patches of snow and ice / dry pavement.