In MMD 161003, Jeff Davis raises a good point about the condition and
air-tightness of the leather packing washers typically found in the
bass-end cavity of the Ampico 'A' take-up spool.  While it is important
that there be no leakage there (and his remedy is appropriate), it
would have little to do with Bill Chapman's original issue.

Leakage here is typically manifest by the switch pneumatic operating
unexpectedly and cutting off the motor when the roll is hitched up to
start, the transmission is in "Play" and the electric switch is turned
on.  This is why some users find it expedient to put the repeat switch
in the "On" position to avoid this problem and perhaps don't quite
understand why it works.

Leakage at this point is not even in the rewind pneumatic "path"
and so cannot trigger a partial rewind [section] collapse to pull the
transmission just enough to disengage the forward driving collar pin.
Even if there is minor steady-state leakage at the rewind hole (8T or
its attached tubing), the rewind section does not operate in a
proportional way.

Since "piloted" valves operate in an all-or-nothing kind of way, they
will not "float" in mid-stroke, delivering a less than full operating
vacuum to the pneumatic, to result in a shift-to-neutral effect.
Generally, only a full, open perforation at 8T will trigger a complete
shift to rewind, and if it doesn't, the fault is more likely to be in
the pneumatic cloth stiffness and/or leakage, linkage friction or
insufficient supply vacuum than it is in leakage in the pilot valve
path.

This is slightly off-topic, but perhaps worthy of repeating: the
spurious switch cut-off when trying to start a roll is frequently
traceable to an entirely different, non-obvious problem at the bass
end of the take-up spool.  Even if the rotating joint, the leather
ring surrounding the take-up spool hole, and the repeat switch are
all entirely leak-free, you may _still_ get spurious switch cut-offs.

If this is happening to you, make this simple test: Disconnect the
tube that connects the take-up spool axial spindle fitting from the
nipple it goes to on the repeat switch and insert a splice nipple
connected to a mouth suction tube, then place your finger over the
take-up spool hole and suck.  It should be absolutely air-tight.

If you detect _any_ leakage at all, remove the axial spindle fitting
from the drawer and examine it closely, under magnification if
necessary.  You will likely find that, through metal fatigue, the
horizontal seam that runs the length of the portion of that fitting
outside the spool box has developed a hairline crack, which can pass
just enough atmosphere to trigger a spurious electrical switch cut off.

I covered this issue in greater detail at
http://www.mmdigest.com/Archives/Digests/201206/2012.06.23.12.html 
which was in response to a previous message posted by Duaine Hechler
at http://www.mmdigest.com/Archives/Digests/201206/2012.06.22.04.html 

John Grant