Q: What should I do if my bass tuning machines rattle, buzz or behave strangely?
A: The performance of both the Suzhou and the Basic machines is greatly affected by the large center screw adjustment. If over-tightened, you can get a clunking or skipping sound when tuning. Over-tightening also causes the thumb piece to loosen. If the screw is left loose, all manner of noises can occur, and the screw can even fall out.
Adjusting the center screw
With the string tension backed off, turn the screw until it makes solid contact, then 1/4 turn further. This adjustment should be checked occasionally.
Repairing a loose thumbpiece
If the thumbpiece loosens and rattles in the end of the shaft, it will need a very simple repair. Place a drop of super-glue in the gap where the shaft holds the thumbpiece, and let it dry. That should do it, but for extra measure you can give the ears of the shaft a gentle squeeze with soft-nosed pliers.
For more advanced work on your machines, you can find a qualified shop here.