"Mike Noel" wrote in message ...
I just noticed today a tendency for my vacuum AI to vibrate a few
millimeters in its pitch axis occasionally, then the movement damps out.
The roll and pitch indication seem to be OK, and the vacuum DG is working
fine. The vacuum guage is at 5.0, right where it belongs. I'm wondering if
this is an early failure indication.

It's caused by engine or prop vibration. The instrument panel
shock mounts might be old and hard, or the prop may need balancing.
Either way, the vibration is reaching the indicator. Next time you
fly, play with RPM settings to see if you can make the indicator
resonate with vibratory fequencies.

Dan