<html> <body> Wimn'Edn'Ricn'all - I think your right.  I may have been thinking of the effects of diminished key dip. However, as Ric and Ed point out, with the jack moved forward, the timing of the jack contact will change, meaning that the singular feeling achieved by the simultaneous (or virtually so) contact of the jack tail and the drop screw, is then staggered, thus extending and distorting the perception of let off.  It's could be argued, perhaps, that, in soft playing, the finger reacts differently to that 'extended' let off and increased friction, thus delivering less energy to the hammer than intended, with the resulting diminished force to achieve checking.  It's quite a reach, I admit, but never underestimate the power of defensiveness to stimulate creative thinking. Ed Foote added the friction of the rep spring in the "grub", either from dirt / gunk build up, or from a dimple being formed, over time by the spring.  This could contribute to poor checking by directly increasing the friction the hammer must overcome in its downward movement, by generating the same finger response as described above, or a combination of the two. Meanwhile, I thought of a few more checking-affecters: 1)Tails mis-faced to backcheck.  VERY common to find them out of plane in angled hammer sections  One side of tail contacts backcheck before other, resulting in very little actual surface interface. 2)Backcheck wire stiffness.  The new Steinway wires are ...(your choice of adjective) stiff.   I think it's a mistake on five counts, no three. One - Harder to regulate Two - Transmit shock of hammer check to finger Five, no Three - Minimizes spring function which, along with complementary surface facing, is the fundamental mechanism creating checking.  Imagine, for example, a backcheck wire with infinite stiffness. Checking would become a function of backcheck felt and leather resilience, surface angle interface, and surface texture interface.  Eliminate the remaining resilience, and you are left with surface geometry.  (It becomes clear that "roughing" the tails is a Band-Aid -potentially destructive- for other issues.) Wim, I'm choosing to ignore your second question, for the moment: <blockquote type=cite class=cite cite="">Does not checking on a medium to soft blow, without too much bobbling, effect the feel of the piano? </blockquote> since the degree to which the problem is noticed is distinct from WHY it is happening.  To that question, I don't believe repinning the rep levers is your answer. It's not logical.   Flash! Here's another I think we didn't mention:  Bedding the keyframe.  Oscillation there could affect checking reliability. Absent actually being there, I'd like to see a thorough check list of all the things we've mentioned...pictures would be, niice. Exhaustive measurements would help. I don't know if it would work, but you could try using gram weights (dampers lifted) to see at what force the checking works or fails. Last flash!  I wonder about the dampers.  If the checking is tenuous, with little spring in the system (stiff wires and hard backchecks), could the impact shock from a falling damper interfere with the grip of the check? There IS an answer out there. David Skolnik </body> </html>