cant change from high to low, im trying to unlock it .

 

What year?????????????????????

 

Ditto from Disco Mike, but try to put it in neutral and let the truck move a little, it may just go right in. Do not grinfd it though.

 

Maybe the linkage is stuck.... check this page

http://home.twcny.rr.com/eeibooks/ro...codifflock.htm

 

the linkage is ok ,I check and locks and unlocks very well. The problem changing from h to low gears.Is a disco 94

 

disco 94. thanks

 

I try that, even in reverse and thenneutral. thanks

 

Check your tire pressure, make sure that the tires on the front are the same PSI and the back are the same PSI.
Then while moving forward at idle try and shift into low.

I have found that if your tire PSI is way off at each wheel it can "bind" up the transfer case making it hard to change gears.

 

I check it , also lift the truck and lose all 4 tires so they can spin freely. thanks

 

Did you remove the center console to check what is going on underneath? Or was there excessive quantity of metal in the oil last time you changed the oil in your t-case? Maybe the problem comes from inside...