I have also found that when stopped and I press down on the diff lock pedal, it doesn't immediately engage. I have to ease forward (or reverse) just a bit for the pedal to fully depress. I think of it kind of like the spindle lock on an angle grinder. There are only a few engagement points, and it takes some rotation to find one, but you don't want to do it "at speed". And Looking4new is right, it is a rather loud snap when it disengages.