Dear MMDers,  I have had one or two suggestions about the bobbling
hammers but as yet no cure.  I did fail to mention that this is
a largely restored action with new felts all round.

I have done some further investigation and found that the damper
springs are much stronger at the bass end which, of course, means that
the stack has a harder job completing the key stroke there.  Is this
normal in an upright?

This will obviously make it more likely that the pneumatics have
a harder job there, compared with the treble end, and so they cause
or contribute to the bobbling problem at the bass end.

James Black