Today has been hell!! We recieved a good deal of snow last night. Well my son goes out to his trusty cherokee 87 4Liter it had a flat. So we changed it and was on our way! well we thought the spar was bad. So I jumped in the 4x4 chevy HD2500 and took the original tire up and plugged it. put the wheel back on and started her up and got going and I noticed my son got stuck??!! The Jeep never and I mean never gets stuck in snow!!! So I went back and said to my son "hey it might work better if you put it in 4wd" He replied "it is". So after trying to shift it over and over to 4wd and nothing just 2wd. I had to follow him home the rest of the way. So at this point where do you think I should start When trouble shooting the 4wd?

 

Do you have the 4 wheel drive shifter with the vacuum shifter? is so check the vacuum hoses that go into the diaphram. If that is all good then check your differential fluid

 

vac disconnect motor on passengers side of front axle, 4 bolts pull it out leave vac lines attached and pull your four wheel drive lever and see if the shift fork moves, requires two people, one in the jeep and one under it

 

HAHA awesome ive fixed mine! have you had yours go out? and well if thats not it then its somethin in your differential! i cant remember the little part names in the differentail but i think its called the rings and pinions that is the problem a lot of times
the ring and pinion may have broke in his differential

 

vac disconnect motor. Is the light coming on?

In my old 88 XJ the 4wheel drive light would not come on, so I knew it was not working. It was the vac disconnect motor I had a mechanic fix it.

Did YOU KNOW: There is a bit in the Haynes manual about 4WD not engaging check tire pressure, if you changed tires and the spare doesn't match or was not properly inflated it could create issues.

they shift into 4wd best when moving.

There is something in the owners manual that you may need to push the accelerator twice to engage the 4WD.

Haynes also says as mentioned check differential and crankcase lubricant.