Sash Balance Size?

Bought a house which was a flip of a flip. While trying to repair this double hung window (will have others to follow) it looks like I've come across a sash balance that has been cobbled together with pieces. The tube itself is 28 inches long with a 5/8" diameter, but the spiral itself fits completely inside of the tube with a blue tip. The outer (top) window may have a 25 inch tube. We've already purchased a 3/8 tube at 28 inches, but when installed, the window couldn't completely close. Help?