Hi, I have an older mountain bike that has the rear brake cable routed through a narrow piece of plastic lining that sort of goes around the seat tube. I can feel a lot of friction in the braking and was wondering if there is a better solution for routing this cable? The little "tunnel" where the brake cable is routed is *almost large enough in dia to fit a pice of brake housing, but it's not quite enough.

Anyone found a good solution to this? Ignore the Surly rear housing stop in the picture, it's just sitting there in case I just opt to run full housing back to it.

Thanks,