Originally Posted by
genejockey
Yeah, that's how I first figured out it needed it. This was after a ride where it really seemed "buzzy" and clunky over some 'textured' asphalt. The first time passed the 'rocking' test okay, but I think it was just not quite tight enough. So the next time, as I say, I tightened it more. I also made sure the stem was really loose before I tightened the cap bolt.
Also, make sure the spacer situation doesn't need to change. The new stem likely had a different stack height than the old one.