My frt locking hubs were frozen in the lock position they would not release. I took off the center cap and tapped lightly on the locking part of hub . I used a small ball pean hammer, After some time the lock released and im all good now. When greasing the outer u joint ,make sure you can turn the axle by hand. If in 2wd and manual hubs unlocked the axle should turn by hand. Prabably the same as f250 f350. Just more useless info.
