<<I recently worked on a Steinway L (431725) that had a clunk sound on key
release.
I couldn't make the noise with the hammer/shank removed. (Moving the
key/whippen assembly)
I observed that the knuckles seemed really hard.>>
Replace one of the knuckles, and I bet the clunk will be gone. You can
lessen the noise by making sure the springs are not excessively strong,
softening the knuckles and seeing that there is no lost mostion between the
jack and knuckle. Also, the jack stop pads are often compacted so that a
small adjustment of the jack position will often move the spoon contact part
to softer felt. You may find that the drop pad on the end of the repetition
lever is so hard that it is noisy.
Good luck,
Ed Foote
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