On my restored 1926/27 Steinway English pedal electric upright Duo-Art
I have a problem with the push rods on the back of the stack.  It is
a two-layer type and although a late-ish instrument does have the full
88 notes with switch blocks.

My problem is that the push rods become stiff towards the end of the
travel when the angle of thrust becomes more extreme and there is
sideways pressure on the rods.  At very low air tension this sometimes
causes "hammer bobbling" as the action does not complete its travel.
I have tried applying graphite to length of the wooden dowels which
although improves the situation does not cure it.  New felt has not
really helped and they are not binding.  I can actually feel the
friction and stiffness when I push up with my fingers on the bottom of
the bellows under the stack.  I am sure that if I could cure this then
the soft playing would be greatly enhanced.

I am going to experiment with PTFE rod replacements for the push rods
but I have seen no mention of this problem anywhere else, am I the only
one?  Is there a proper technical cure?

Regards, James Black, UK