The Asin hub on my 1992 Toyota is extremely hard to lock or unlock currently having to use a screw driver to even move it to the lock or free position anyone know what may cause this?

 

Probably just needing to be disassembled, cleaned, and re-greased. They're not too hard to rehabilitate. There are some good writeups on this forum and elsewhere on how to do it, and no special tools are required. Just do some online reading, block out an afternoon, and go for it.

Even at best they can be kind of stiff. I made a tool from a piece of 2x2" oak about 4 inches long, with a groove cut in it that just fits over the raised bar in the center of the hub. That gives my wimpy fingers extra leverage to turn the mechanism. I keep it in the driver's side door pocket.

 

Yup, time to tear down and rehab them. Did mine in a couple hours tops. Easy job. Grab some snap ring plyers and you're set.

 

over greasing can be the problem from what I've read here

 

Too much grease inside the hub can cause the hub not to lock and unlock correctly, but I don't think too much grease alone can make the selector itself hard to turn.

Its more likely a lack of lube, and corrosion, that is causing the knob to be stiff.

Also, just because the knob is turned to 'lock' or 'free', does'nt necessarily mean that it is so. Turning the knob does not result in a positive action, it only applies spring pressure, one way or the other, to move the splined locking collar in or out of battery.

The spring that pushes and pulls the locking collar is fairly light and too much, or too stiff grease, can impede the collars motion.