Originally Posted by
dr_lha
Before replacing the headset, try replacing the bearing cages with loose ball bearings, which often fixes the issue. See Sheldon for details:
Servicing Bicycle Headsets
This. Or replaced the caged bearings with caged bearings that have a different number of balls. That also fixes it. Replacing the bearings with loose bearings will, 98% of the time, fix it. Do that first.
Indexing is EXTREMELY obvious. If you can't feel it when you turn the handlebars back and forth, it's not indexed. There is absolutely no danger in continuing to ride. An indexed headset is still a perfectly functional headset. The only "danger" is that the wheel may want to stay straight if you're trying to balance no-handed.