Jack Slipping?

[Greg Casper]

I just got back from a customer who has a Kawai grand with one key they said
wasn't working. Turns out it works pretty well UNLESS you strike the key
hard. When you do that, the hammer barely even moves. It looks to me like
the jack is sitting too far forward on the knuckle, but since I didn't have
a jack screw adjusting tool with me (this was ONLY supposed to be a tuning..
and stupid me didn't take all the tools) I couldn't regulate that out to
determine if that's the ONLY issue. Any opinions on what else might cause
this situation? The backcheck almost seemed to be catching the hammer on
it's way UP to the strings, but since it's only happening on a strong blow
to the key I think it just LOOKS like it's catching, since there is almost
no upward movement of the hammer when this occurs. Ideas?

Greg Casper
San Jose, CA