Many helpful suggestions for troubleshooting and adjusting have
been submitted recently.  Before making any of the mechanical
adjustments, I recommend always testing the tracking pneumatic
itself for airtightness, to see that the two opposing pneumatics
are equally airtight and balance each other perfectly.

Disconnect the three tubes connected to the elbows at the hinge end,
noting which tube was attached to each elbow so they can be reattached
in the right order.  Attach temporary tubes for testing the pneumatic.
Apply suction to the larger supply tube while closing off the two
smaller tubes tightly with your thumbs or fingers.  The pneumatic
should slowly go to its centered position.

Open one small tube and watch it go to one side.  Close that tube,
open the other one, and watch it go to the other side.  Close both
tubes again to make sure it centers itself.  Then open both small
tubes.  It should stay centered, although as mentioned in an earlier
posting, that condition (caused by both tracker ears being opened
at the same time) should never occur when playing any roll of normal
width.  All of these tests are done with suction applied to the supply
elbow.

If the pneumatic doesn't center itself, either one internal bleed is
plugged, or one side of the pneumatic is less airtight than the other.
The latter is frequently the case, either with old cloth or after one's
first attempt to recover one of these units.  If not symmetrically
airtight, check the corners and areas where layers of cloth overlap.

Much of the motor cloth (double-weight pneumatic cloth) made in the
1980s is starting to leak now, so don't assume that a fine 30-year-old
recovering job is still perfect.  Many examples of 1980s and earlier
double-weight cotton motor cloth have begun to go bad over the last
ten years, just as some of the original cloth did by the 1950s.  This
is regardless of the color of the cloth or its vendor.

(I theorize that perhaps something about laminating a thin layer of
rubber between two layers of cloth causes the rubber to turn hard
sooner than in single-weight pneumatic cloth, but I don't know of a way
to verify this except by watching the cloth age.)

Once you establish that the pneumatic doesn't have any tendency
whatsoever to pull to one side when the two small tubes are closed,
proceed to test the tracker ears (by attaching a testing tube to each
one and sucking on it) and the rewind cutout pouch block.  Then proceed
with the mechanical adjustments.

Art Reblitz - Reblitz Restorations Inc.
Colorado Springs, Colorado, USA
http://www.reblitzrestorations.com/