Plowing snow today I decided to head out in my back yard where there is steep hills. I found that I needed my differential lock. Ok fine, I got up the steep hill in my back yard and back to the drive way. My differential lock would not unlock. I could not steer or anything. I have had trouble with this before and complained to my dealer. The only way I could get it out in the past was to hit one side of the brakes while moving and it would come out, no big deal. Today it would not come out for anything. I finally had to put a pry bar underneath the pedal using a 2 x 4 for height. It finally popped out but I did have to apply a lot of pressure. All you New Holland mechanics give me some pointers on what I should do to prevent this in the future other than don't use the differential lock.
Re: Differential Lock
The difflock operating rod goes all the way through the rear axle center section, protruding on both sides. This allows for easy, cheap installation of the difflock pedal on either side, depending on transmission option. The problem is there are TWO areas of the shaft that must move through O-ring seals with relative ease with less than regular use. Figure out which way the shaft moves, and clean a portion of either side equal to the amount that must pass in and out of the case, probably less than 1.5 inches. After cleaning, spray liberally with white grease, your choice of penetrant, or coat with never-sieze. Someone will bark about never-sieze not being a lubricant, and being somewhat abraisive. Those folks don't have to use it. I happen to love the stuff. There is plenty of spring inside the case to return a properly free shaft if the differential isn't under torque load. Very , very few problems internally with this system, usually a dry shaft causes your symptoms. Be sure the pedal pivot is not part of the problem.
Re: Differential Lock
I agree with the clean & lube.
Did you let it free, turn the steering in both directions while traveling slowly?
Did you try backing up & turning both directions? (If you have mis-matched front/rear tires, the binding in 4wd could be causing the problem - reverse would solve that.)
Did you press one brake, then the other, quite firmly?
I would not pry the pedal up as you did, I don't think the linkage is real strong in that direction.