Did you hear a grinding noise? As ATC Crazy said, the splines have to line up... but that's not always easy to do after you're already stuck. If you can gently get the truck to rock a few inches in either direction that should be enough. If, however, you just flipped the switch, threw it in drive and hit the gas, I can see why it didn't engage. The tolerances on the splines are tight, as they should be, so if the axle shaft and tire are spinning at drastically different speeds they tend to just skip over each other ...generally with a grinding noise.

This can easily happen when you are stuck, even if you are trying to go easy, because your tires are held in place. As you lean into the gas, the pent up energy in the drive line builds until one of the rear tires breaks loose. Once that tire breaks loose things start spinning pretty rapidly as all of that energy is released - meaning you don't get that nice, fine, gentle movement needed to allow the splines to engage.

Compounding this is the multiplication effect of differentials when one wheel is held in place. One of the hubs will generally engage fairly easily, but when it does the axle shaft on the other side will now spin at twice the normal speed, making it that much harder to get the splines to line up without skipping over each other.

 

And NEVER use 4wd on a paved, dry surface, unless it is perfectly straight. Any turns or curves will induce a LOT of stress to the driveline components that can & will, over time, cause premature wear or breakage.

 

I had no grinding. I also felt the clunk in the transfer case. The right rear tire was the only one spinning. The dashboard confirmed I was in 4lo. The truck did not move till I turned the hubs from auto to lock. Is there any problem leaving the hubs locked with the truck in 2 wheel drive.
I even pulled the ****, I think that is supposed to lock the rear differential. Thanks

 

No. You might lose a fraction of a MPG from extra rotating mass. But there is no mechanical issue with doing this. When I had my '01 with manual hubs/manual 4x4 I would lock them in the fall, leave them locked all winter, and unlock in the spring.

 

Leaving them locked will add wear to the drive line and cost you some MPG, but otherwise be ok. Might be a problem with your vacuum engaging them automagically.

 

Hummm vacuum. I did have a level kit installed. Could that have played into the vacuum line being jacked with. Is there any way to get a diagram of these lines from the hubs to where they run in the engine compartment. Thanks.

 

Possibly if something was disturbed. I don't have a diagram but they shouldn't be too hard to trace. Valve is by the coolant tank and there should be a line going into the back of each knuckle.

 

Thanks I did a search and found more info.. It told how to test with a vacuum pump, which I don't have. I will do some looking around on the truck tomorrow.

 

 

That sounds easy enough. I'm still going to check the vacuum lines to see if there is anything wrong with them. Thanks.

 

 

I think it varies greatly based upon what you mean by "off-road." If you are heading into mud, water, snow...yeah, I'd pop into 4x4 immediately. If I'm heading up a fire trail with loose gravel, dirt, sand, roots, rocks..nope, I'll go in 2WD until I need it.

I mean, once you are off any high traction surface like pavement or concrete, you can use 4x4 without any harm but sometimes it's nice to have steering for awhile too.