This seems to be a more common problem with single cams, the sharp angle to give the solid feel seems to be more "harsh" on the cable. I've seen guys who used BCY #62 in .018 I believe instead of the .021. Just my own opinion that I would think the .021 is too big a diameter (nothing to back that up though). Make sure it is also served so when you twist the cable up it is tightening the serving and not loosening it. I've used 2D for all mine and don't have a problem so wouldn't think it is the material.