So wait, your top cap broke and hasn't been replaced? That's the problem. The top cap you broke isn't cosmetic, it was probably just cheap.
The screw pushes the top cap down, which pushes the stem down, which tightens the bearings. Your top cap is gone, so tightening the screw doesn't do anything to the bearing.Get a new top cap and it should work normally.
If you've got the stem on tight now and the bearing isn't loose then it's fine for now.
Last edited by Yellowbeard; 06-03-15 at 07:13 AM.