Changing Out Thayer Shanks

[pcpoulson@sbcglobal.net]

Hello All: I am in the process of changing over a grand action from Thayer 
type shanks to modern knuckled shanks. Brooks Ltd. hung the hammers and 
matched up the shanks and flanges as close as possible. There is a 
difference of about 1 mm in the height of the flange center pin between the 
old (higher) ones and new (lower)  ones. I have been able to regulate the 
action fairly well, but have been having trouble getting the correct amount 
of drop on some notes. Most of the notes regulate well, but a few in the 
upper treble will not drop after letoff. I have re-regulated them several 
times, and checked for excessive felt wear on these notes, but nothing seems 
to change. A neighboring note will regulate correctly, and then the one next 
to it won't. I'm stumped. Any suggestion?
Thanks,
Patrick C. Poulson
Registered Piano Technician
Piano Technicians Guild