Hi guys! Sorry for the noob question but... this snow storm has really hit my town hard, we're about 48 inches under snow.. Anyway this is the first chance I'm getting to use the 4wd option on my 03 xterra XE so I'm excited! How do i shift from 2H to 4H? Do I shift it while moving at a certain speed or can I do it parked? Also, I read up on something called hubs and I have absolutely no idea on what that stuff is. I just don't want to mess up my car and shift into 4H properly. Can anybody give me a few pointers on how ?
Thanks a bunch, Joe
I am guessing you have an automatic transmission...
If you look on the driver's side sun visor, there may still be a decal with instructions/a cheat sheet...and in the glove box, there might still be an owners manual.
If what this post seems unclear, look at those too.
There is a t-case shift lever on your console, to the left of the transmission shifter.
All the way to the front for that lever is 2H. Pull it back to you, and the green 4wd icon will light on your dash.
The truck has what are called autohubs....essentially, they are what make the shafts from the front differential turn the front tires.
So, when you pull back on the t-case (Transfer case) lever, you are sending engine power to the front diff...so that the front diff turns the shafts in the hubs.
The tires need to roll forward about 3 - 12 ' to engage the hub gears....so that the shafts turn the tires.
That means that after you shift into 4wd, UNTIL you roll a few feet, and, even thought the dash icon says you're in 4wd....the shafts are not engaging the gears to turn the tires.
So, shift it into 4wd, and, then, go forward a few feet...and, after THAT, then, you are in 4wd.
You can back up or go forward after that, in 4wd...the forward part is JUST to lock the hubs.
So, if backing out of a parking spot....you'd be backing in 2wd even after shifting into 4wd for example.
Once you have locked the hubs though, by going forward in 4wd, the hubs stay locked, until you shift back into 2wd, AND GO BACKWARDS A FEW FEET...to unlock them.
So, going backwards, if still in 4wd, means you are going backwards with 4wd...they don't unlock.
Generally, to avoid getting stuck, you'd get it into 4wd and locked...before parking, so, if snowed in, etc...your hubs are already locked when you go to drive out of the drift, etc.
That way, if the rig is packed in deep snow and can't roll forward enough, you don't need it to.
If you parked in 2wd, with the hubs unlocked...well, hopefully, you can roll forward enough to engage 4wd all the way.
--------------------------------
VERY IMPORTANT:
If you are not used to 4wd, and have not used it...just remember that is only helps to go....not stop or turn.
The traction the tires have is exactly the same.
If you actually NEED 4wd because its that slippery...that means you go SLOW.
Otherwise, its TOO EASY to go too fast, and, then, realize you can't stop in time, or turn sharply enough, to avoid an accident/spinning out, etc.
IE: Just because you CAN go faster, DON'T.
-----------------------------
As for speed to engage, just shift into 4wd when parked, and go forward. At low speeds, you can get into 4wd too, but, as a newb, don't....just stop, or all but stop, to do it.
When its very slippery, the tires act like you downshifted when engine drag kicks in...and shifting on the move can make the rig swing, plow or crab if the conditions are bad enough.
If you use 4wd to get out onto plowed roads, shift back into 2wd to avoid drivetrain damage as soon as its not slippery. You do not need to go backwards to unlock the hubs though...so if you hit a stretch of slippery stuff, the hubs are already locked.
Going back into 2wd on the fly is easy, just push the lever forward again...no need to stop first. Less than 50 mph IIRC is the top speed.
Hope that helps!
all this is news to me... Good to know though. On drivers side under the sun visor there is a little instruction sticker stuck on but after reading about the hub caps and stuff I wanted to know a little bit more.. So say I'm on level ground, I turn on my car as normal. I would put the car on neutral (still not moving) and switch it into 4H? Then drive forward a few feet to engage the 4wd? after I do that it would be fine for me to just drive as normal? As for the slippery roads and stuff, it's not too bad but there have been accidents so I don't want to risk just driving in rwd. 
