How to tell if 4wd is working?
 

Recently purchased a 2004 Screw. Got a little snow today. I headed out in 2wd and the rear broke loose. I switched to 4wd on a hill and found the rear was still breaking loose. The tires aren't the best and I didn't have any weight in the back yet. I have been driving only AWD for the last decade, so maybe I've just forgotten life with 4wd, but I was surprised this kept happening for the rest of the drive. At a stop sign, I swear the front tires were on wet pavement and the rear end which was on a little snow broke loose. Should I be chasing this 4wd thing? What should I do to test it besides getting myself stuck and seeing if I can get it out of the mud? Sorry if this is a question already answered, but I searched and couldn't find a thread.

if the asphalt is wet (of course, shouldn't be dry asphalt), turn, see if the truck binds a bit (you should notice it). I can tell even in the snow with mine while turning that the front is binding a bit (but I do have winter tires too - more grippy). Even with what you've tried, it shouldn't break loose in the back like that. I can do a 4-wheel spin in the snow but I can definitely tell that I'm in 4x4 vs 4x2. The back doesn't kick out near the same IMO.

Another check (a bit more intensive of course), put it in 4x4, jack up the front, start truck, put it in 4x4, see if the front tire turns or not. If it turns freely, see if the half-shaft is turning (hubs locking), or if the diff is simply turning. Most common cases are the IWE solenoid, IWE Actuators, or transfer case motor fails.

Thanks for your help. I didn't have any binding when turning, so I jacked the thing up and had an actuator that wasn't locking in. I didn't have anything to measure vacuum and it still seemed screwy. With another snow coming, I relented and took it to the shop. One side was stuck in and the other stuck out. They said the vacuum was fine. I do wonder if this means there is occasionally water in the line that leads to corrosion.

Now I just have to work through the water leak on the passenger side door…

Thanks again for the help.