1984 s-10

I just got this truck a couple of months ago and while driving down the road the 4 wheel drive will engage. It has happened to me several times and i have checked and the little lever doesn't move. When it happens it doesn't go all the way in so i hear this horrid gear grinding sound so i switch it in and out of 4 wheel drive. This makes it go back into 2 wheel but the 4 wheel light stays for quite a while. Any Ideas on why it does this and how to fix it?

I'll bet your vacuum valve mounted on your transfer case is stuck, letting the front differential engage or partially engage on its own, common problem! They're not very expensive i'd try that first. When you pull it out youll probably see that the plunger is stuck up inside the valve. Its on the upper left hand side of the transfer case with 3 vacuum hoses going into it. Hope this helps!!;)

yeah my friend had the same problem

get a posi-lock from summit racing. it is a cable that runs through the fire wall from under your dash to the front axle that by passes the vacuum system to engage the front pumpkin. my vacuum switch went twice in 2 years and at $54 a piece the $120 for the posi-lock seemed like a better fix and i physically control when the axle is engaged. another perk is that you can use it to put your truck into 2-wheel low.