I installed several Luke's with no problem till I got to one where the stock ball was worn out. Too much horizontal movement. New ball end fixed it right up. Hard to tell how worn they are by just looking, you need a new ball to caliper off of to see that only a few thousandths is all it takes to cause slop.

 

When you got the worn one, did it move when it was installed properly? How did you know it was worn?