you will find 2 holes in the raised bit on the diff tube inside these are 2 allen key grub screws which hold the sun gear shaft in place. Back off both grub screws 180 degrees then turn one screw in and the other screw out an equal amount untill you get the locking effect you want and then tighten the screw you were backing out and your done. If you don't get the locking effect reverse the direction you are turning the grub screws. if you are still not getting any effect you have a problem with the thrust bearing inside the diff .