<HTML>Thanks to all that offered advice on solving my problem First a couple of observations. These are new hammers shanks & flanges, but I didn't hang them. I had previously shaped the tails On the first four notes in the treble, I roughed the tails, filed down the edges of the tail, and reset the back checks, making the rake more "flat," I also allowed the hammer to check lower and reduced the rep spring. That helped some, but not enough. I looked at some of the other suggestions, but none really seem to apply. Out of the piano, the action behaves perfectly. But once it is in the piano the bobbling problem doesn't go away. Finally I took some measurements, and maybe this is the problem. What is supposed to be the distance from the center pin to the end of the hammer? Here is what I found. note 1    5 1/4 note 26       5 1/8 note 27       5 3/16 note 41  5 1/4 note 54       5 7/32 note 55  5 9/32 note 72  5 1/4 (As I said, I didn't hang these hammers, and neither did Steinway) Can any one tell me if these measurements are related to the problem? Wim </HTML>