Autopilot Question

We have the Piper Autocontrol IIIB in our '74 Pathfinder. It has worked
fairly well since Day One, failing only when our vacuum instruments each
went Tango Uniform, in the space of six weeks.

However, the "heading bug" on our DG has always off by about 10 degrees. If
we wanted to fly 180 degrees, we had to set the bug to 170 on the DG. This
was mildly annoying, but easy to work around.

When the DG died, and we got our newly rebuilt unit (from the Gyro House), I
was expecting the heading bug to be PERFECT. Well, imagine my surprise when
the NEW heading bug is ALSO off -- by exactly the same amount! We *still*
have to set the bug on 170 to fly 180!

It's apparent that there is some other adjustment out of whack. But what?

Even my A&P (who admits he's no autopilot expert) was completely surprised
that our new DG didn't fix the problem.

What the heck is up? What needs to be adjusted, if not the DG?

Thanks!
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"