Unimog Club UK

The adjuster screw, is it just turning, not doing anything? or seized?
If it`s just turning, you might be lucky and the piston has seized slightly, and as you wound the adjuster back the mechanism inside the piston that adjusts it  has come unclipped. It is held inside the piston with a snap ring, you need to remove the piston, and the bit that snaps inside it, press the adjuster back inside the piston, and fit it back into the caliper, carefully winding the adjuster back as you push the piston back.
The allen key part of the adjuster is held in place with a circlip and a washer, if you remove them and turn the allen key to undo? (from memory) the adjuster should unwind its self out on the helix gear, if you want to check condition of the gear.
For changing the pads the screw does not need to be removed, I find easing the piston back as winding it back on the adjuster helps.