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I have an old threaded headset and quill stem. Recently I overhauled the headset; replacing the bearing sleeves with loose bearings (filled to max and removed 1 bearing). The stem was also found to be too large to fit back in, and was replaced with a proper fitting one by a bicycle shop that specializes in older used bikes.

Now when I am riding I get this strange gyroscopic effect while riding (see this post for similar issue)

When riding in a straight line I can feel a push and pull to one side or the other, as if a ghost is steering my handlebars in millimeter amount, but enough to notice. It almost feels as if my headset is drunk, wobbling around in circles. A similar feeling would be turning your neck in circles as if stretching your neck... just not as intensely.

I've tried loosening the headset to the point where when I pick up the bike the handlebar smoothly drifts over to one side from the weight of the wheel being picked up.

Does it matter if the quill stem is tightened or loosened after the threaded headset is adjusted? I don't think it does.

I'm lost here! Please help!

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  • If the work was done at the shop then take it back. It's likely too tight, but IIRC it can also be too loose. Too tight: doesn't move freely; too loose: can feel movement. Both tests with bike on the work stand. – andy256 May 3 '15 at 22:14
  • It's unclear what parts you replaced. If you replaced the entire fork you may have gotten one with a different amount of "rake" from the original, and that "rake" may be inappropriate for the head tube angle of the frame. If it was really just the stem (the part that holds the handlebar) that was replaced then it may be too small and may be wobbling in the tube of the fork. – Daniel R Hicks May 4 '15 at 0:49
  • Another point is the fore/aft extension of the stem. Moving the handlebar forward or back relative to the steering axis (due to a different stem) causes a significant change in handling characteristics. – Daniel R Hicks May 4 '15 at 2:35
  • I adjusted the headset and loosened it... and it seemed to have fixed the issue. Will let topic stand while I ride I tomorrow and see if the issue revisits – 835 May 4 '15 at 3:35
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    @Criggie I have no idea what the problem was. I ended up bringing my replaced stem and bearings to a different bike shop to be adjusted, and they managed to fix it. It has been fine since. In fact, it's been the most fun bike I've ever ridden! – 835 Oct 16 '15 at 11:04
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The side to side you're feeling is that your headset is binding up. This can either be because it's too tight or because you've put some part of the headset in upside down (i.e. a bearing cage or installed the cups the wrong way around) or something is out of alignment. It is especially a problem on the bottom cup, when the headset is under load and can't micro-adjust the wheel as you ride.

Check everything is seated properly and in alignment (try putting a sheet of paper between the cups/races and the frame. Check all your bearings are clean and lubricated and nothing is installed backwards.

When tightening your headset you want it tight enough that there is no play, and no tighter. To check for play put the bike on the ground, hold the front brake and push/pull on the handlebars. Then do it with the wheel turned 90° left and right. Ensure you're not tightening the top race when tightening the lock nut.

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