I've been trying to figure out the proper way to use the 4wd in my toop, I currently have the auto hubs on it, however almost at random times I get the 4wd light and I can shift between 4h and 2h and it runs like a champ however other times I will shift into 4h and nothing happens and no light, even after reversing and etc, I think I'm just not doing something correctly and the hubs or something won't unlock. Any insight would be greatly appreciated I'm kind of new to all this,

 

No light when shifting into 4wd? that means the gear locking shaft collar is not sliding over into the locked position. The transfer case is in 4wd, but the front axle is not in 4wd.

On my 96, it is controlled by a vacuum diaphragm and electric vacuum switches apply vacuum to one side or the other side, The indicator switch on the axle at the servo diaphragm turns lamp on and off on the dash. So, when you push lever into 4wd, an electric vacuum solenoid coil applies vacuum and it pulls the gear coupling into place on the front axle locking the front axles shafts together, and vice Versa for 2wd.

I had to replace one of my electric vacuum solenoids as it got stuck. There are 2, one grey, one blue and they are different.
Other problem I had, the vacuum reservoir tank on the driver frame rail rusted out. I replaced with a plastic one made for a different car.
There is also a vacuum filter on the driver side shock tower to keep dirt from getting pulled into the system.
Vacuum is from an attachment hose port on the intake manifold. It may seem a little complex but easily understood how it works.

I think the main potential failures are the electric solenoid vacuum valves or the rubber diaphragm. I found a valve on Ebay.
something might work that is from a different car, each valve has to apply vacuum while releasing the other side to atmospheric pressure.

I wish they had used a spring loaded mechanical cable line to the front axle instead which might be more long term reliable.

 

I also note that the 4WD dash light may stay on when shifting back to 2WD on the shift lever. The Transfer case being mechanically connected goes back to 2wd, but the front axle being under driveline pressure may stay locked. Turn the wheel while driving and it will pull the shaft coupling collar back uncoupling the front axles from each other.

Not a big deal as on most 4wd trucks, it is always locked be design.

If you really wanted, you could permanently lock the front axle by modifying the diaphragm to block it into the locked position all the time.
The use the shift lever to shift in and out of 4WD and 2WD.

But you have to do the shifting like all trucks then, no more shift on the fly, shift only when stopped.

 

LOL, the OP posted this over 8 mos ago and hasn't been back since. He probably figured it out.

 

Still useful info for someone else possibly.

 

That's true