I recently acquired a 1927 5'8" Knabe Ampico A that had been rebuilt
about 10 years ago.  It is a beautiful, original walnut finish piano
that has been very well cared for.  As I gradually work through minor
issues, one issue has come up that I am looking for some guidance with.

This piano has its original lead tubing that is beginning to fail,
so that is one of the first issues I will soon address.  I started
investigating the treble expression mechanism, as I did not see much
movement on that side with the piano operating.  I thought that I might
have leakage through the lead tubing.  So, I went further back in the
tubing, to the expression cut-out block, to eliminate the possibility
of leakage through the lead in the drawer.

Looking at 2T, 4T & 6T, when I remove a tube from one of these, there
is suction that doesn't stop.  If I remove a corresponding tube from
the bass side, say 2B, 4B, 6B, there is momentary suction and then it
stops.  I understand that this mechanism works on a lock and cancel
principle, so I am thinking that something is preventing the valves on
the treble side from locking.

On observing both expression mechanisms while playing a roll, I see
that there is movement in the bass side spring pneumatic but not the
treble.  Reaching up on top of the expression mechanism I can feel
movement in the bass side intensity pneumatics, but not the treble.

Has anyone experienced a similar problem?  I am anxious to hear ideas
before I tear into the expression mechanism.

Thank you,
John Kiszla
Vallejo, California 

 [ photo of the 1927 Knabe
 [ http://www.mmdigest.com/Attachments/18/01/31/180131_111608_Knabe%20front.jpg