Half the work on keeping sidepulls centered on a frame should to make sure that your brake cable routing and length will excert the least amount of pulling or pushing loads on the caliper when the handlebar is turned through it's maximum angles fron=m the frame....but some brake calipers do seem to resist centering despite any sort of adjustment you may do to it or the cables (I remember Weinmann sidepull brakes used to be stubborn for me back in the 80's. I pretty much had to adjust them for dentering after every ride.). But do check your cable length and routing very careful, and you will be at least half way to getting your brakes to remain centered on you bike...