Syncro--
The owners, service, and parts manuals show the button, linkage, and mechanism for the diff lock but none of it is on the machine, nor does it look like it ever was.....
In that case I guess it really was an option, I just have not seen a 580CK that didn't have it. In a pinch you can ease on the brakes while giving it throttle to give you a little extra traction, not as good as a locked diff though. Those were good ol machines in their day, but the loaders were their weak point. Twisting of the loader arms and weld breakage was common, had to be careful with sudden stops!
