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MMD > Archives > September 2003 > 2003.09.03 > 05Prev  Next

Leaks in Air Motor System
By John A. Tuttle

Hi All,  In reply to Michael Hamilton's question, there are only
a few things that will cause the Tempo of the music (or Air Motor)
to vary.  One way to approach the problem is to eliminate some of the

First, test the air motor and find out if there are any problems.
In the case of older air motors, the cloth may be getting stiff or
leaky.  The sliding valves may be leaking, or there may be an internal
leak in the vacuum supply channel.  To help people test their air motor
and the air motor governor, I created a few web pages some years ago.
They're located at:

Regarding the Forward-Roll friction brake in the transmission, the
biggest single problem I encounter on a regular basis is that the felt
pad has become contaminated with grease.  This causes too much drag and
forces the air motor to work much harder than normal.  A quick visual
inspection will tell you if the pad is contaminated.

Another indication that the brake has too much drag is that the Tempo
has to be set to an increasingly higher speed to maintain the proper
tempo.  The solution to the problem is simple: just replace the pad and
clean the brake drum with lacquer thinner.  It's also wise to clean the
surrounding area so that the problem doesn't come back within a few
months (or years).

Regarding the hissing, or leakage, in the air motor governor (where the
tempo rod and fast-reroll rod pass into the governor), a certain amount
of leakage is totally normal, and it will not adversely effect the
Tempo.  Even in extreme cases, such leakage does not effect the Tempo.
However, it does effect the amount of effort required to pump the foot
pedals (as does any internal leakage in the entire payer system).

If the leakage in the governor is extreme, replace the felt bushings.
They are not difficult to replace.  However, doing so requires removal
of the linkage.  This in turn requires that the linkage be recalibrated
once the linkage is put back together.  This in turn requires the use
of a test roll to regulate the governor.

Further information about "Testing Your Player" can be found at

Hope this helps.


John A. Tuttle
Brick, NJ, USA

(Message sent Wed 3 Sep 2003, 14:11:49 GMT, from time zone GMT-0400.)

Key Words in Subject:  Air, Leaks, Motor, System

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