torchard wrote:but my sense is that when shifting the transfer case to 4wd high or low it fires a solenoid or some such which engages the hub.
Notice that our hubs say "auto unlocking" not "auto locking" Subtle difference.
Think more like a bolt being tightened up. The wheel side of the hub is turning all the time. When you put it into 4Hi for the first time, the transfer case starts to turn the front drive shaft, diff, and half-shafts into the hubs. That makes the inner side of the hubs turn and (let's pretend) expand to jam its teeth against the outer teeth that are part of the wheel side that are already turning.
That's why you have to be driving in a straight line, otherwise there is a differential between the hub speed and the half-shaft speed. And if you switch to 4H with hubs unlocked and you are stuck, then it will engage without the outer side turning. Can you say "loud clunk".
Your hubs are now locked, and stay that way until...
torchard wrote:The hubs will stay engaged when in forward or reverse and disengage only when transfer case is moved back to 2wd mode. Does this sound correct?
Yup. When you back up in 2H, the transfer case stops turning the driveshaft, diff and half-shafts. But they are still turning because they are connected to the hubs. But by going in reverse, the inside of the hub "unscrews" from outside of the hub. You are now unlocked, and the half-shaft, diff, and driveshaft stop turning.
This all might not be technically correct, but that's how I think of it.
The "wheel lock" light detects turning of the driveshaft, rather than the exact setting of the hub. So the light isn't always right. The other day, I backed up a couple of feet in 2H. The light stayed on, so I thought I still had locked hubs. When I went to put it into 4H, there was grinding noise. Yanked lever back into 4H, but there was a loud whining. So I stopped, put it into 4H, went forward and the hubs locked again. Clearly, they weren't locked, and not locked either, but 1/2 way in between. Oops.
I also notice that when I park and shut off the engine with the hubs locked, when I restart the wheel lock light will be off until I move a little.