Auto hubs sense the torque when you are in 4x4 and automatically lock in. So yes, you put the transfer case in 4x4 and go. You do nothing with the hubs.

With manual hubs you must get out and lock them in shift into 4x4 and go.

 

With the factory automatic hubs you shifted to 4 wheel drive while stopped and began driving the hubs would lock. To unlock the hubs you shifted back to 2 wheel drive and then backed up a few feet and the hubs would unlock. Or if you had been backing up last in 4 wheel drive you would drive forward to unlock the hubs.

This was how it was supposed to work. As the hubs aged sometimes they would not unlock correctly and then of course sometimes they would fail to lock which left you stranded in 2 wheel drive.

It has probably been at least 10 years since I drove a truck with the automatic hubs. So I am a bit foggy. I can’t remember exactly how it felt when one hub failed to unlock. I know I got to where I could tell it. Perhaps steering wheel wobble on a turn…….. I switched to manual lock out hubs and then blew the engine on the old ’84 and bought a ‘77 with the full time four wheel drive. Those old systems have never been matched for serviceability and safety in my book.

 

so i know it isn't vacuum operated, but i don't know where to start looking to correct the problem.
the t-case is operational, 4wd light comes on but i don't think the auto hubs are locking. i have not had a chance to jack the front of the truck up to make sure though. should i do this first or try something else?

 

Yes, jack it up and check it out.

Did you get this truck directly from your father-in-law? I guess what I am really asking is when was the four wheel drive last known to be working? Could someone have removed the front driveshaft? I have seen that happen! I have done it too. My 77 had front pinion bearings go out and caused a terrible viabration.... off came the front shaft until I got around to putting in a different front axle.

 

yes i got it directly from him and he purchased it new. the truck has sat for 2years up until i got it a month or so ago. he said he has never done anything to it and the 4wd has always worked except once when he had a load of rocks on and was backed down a steep hill. i guess the neighbors tractor pulled him 2/3 of the way up the hill and the 4wd would engage then. he said it had always worked after that with no problems and he's kinda shocked that i'm having trouble with it now.

 

to check the hubs i would have to jack up both front tires, engage the 4wd and turn one and see if the other turns. right? but if it is in gear they wouldn't turn at all if the hubs are working correctly. right?

 

Setting for two years the hubs might have got sticky. A good cleaning might help them. I never tried working on them my brother used to rebuild them for one of his bosses. I think mine are still in an old cabinet in the shed. I should take a look at them. Maybe later when I go out to push snow. It is -2º out right now so I am not doing much!

Yes put it in 4X4 and jack it up. Since these hubs lock when you drive in four wheel drive you probably should drive it in four wheel drive a ways before you jack up a wheel. I would probably just jack up one wheel at a time and see if the wheel will turn. If you jack up both of them and turn one wheel if both hubs are locked the other wheel will turn in the opposite direction. My guess is one hub is locking and one is not. Oh for a good memory! It seemed to usually be one hub that always failed first but I don’t remember which.

Something else you may try is jack up the back end so it does not move and see if the front hubs will lock by engaging the clutch with the engine running to spin the front axles.

 

Truck in drive and 4 wheel drive. Jack up one front tire and try to turn by hand. If the tire turns the hub is not locking in. Let that side down and repeat on the other side to make sure you know which one is bad or maybe both.

The differential feature will allow the tires to turn when both front wheels are jacked up with the truck in gear. Putting the truck in gear locks the ring and pinion but not the axles.

 

it's alive! i tried it again 3 times this morning and it didn't work so i jacked each side up and turned the wheel back and forth and the hubs finally locked in. i have put it in 4wd 6 times and it has worked everytime! thank ya'll for the help!

 

Glad it is working. You will find that with a little care and maintenance these trucks will last a life time. After 26 years the hubs deserve a good cleaning. If 4 wheel drive is something you are going to depend on you should service those hubs whether you do it or you have it done. Sounds like the grease in there is old and hard or contaminated and if it is they will wear/fail prematurely with use. Once the grease solidifies it can no longer flow to where it is needed.