I pumped a hand grease gun six times and it pushed the pivot bushing off the end about two inches and bent the flat steel support bracket that the pivot mounts to. I had to take it apart. and straighten it and then put the bushing back in the center pivot.
On my tractor, (Kubota L3830), you are supposed to unscrew a grease release plug located on the outside of the axle/pivot housing to release any pressure as you pump new grease in. I pump a little in and a little comes out the plug hole. I would guess your tractor would have a grease release plug, too. Check the owner's manual...I'll bet it will be there.