I and trying to troubleshoot a pre 85 bird with AP-105 and FD-109 systems. The issue is that with INS as a vertical reference and autopilot engaged both control wheels will experience a frequent uncommanded movement left and right in a shuddering fashion. It doesnt move a lot but it will go from steady and smooth to rapid shudders in the blink of an eye. With VG as a vertical reference it mainly functions correctly but will radomly experience a sharp and rapid right hard-over. This is with AP coupled regardless of pilot or copilot side or uncoupled with AP engaged and in both HDG or NAV selected.
So far we have changed several AP AMPS, Aileron servo motor, Aileron drum and bracket assy, K-relays associated with HDG, swapped FD computers, swapped mode couplers, changed 2 AP controllers, and shot wires associated with hdg and roll data with no loss of continuity. Also slaved in an Airspeed sensor, and changed an elevator servo.
Any ideas or inputs that may be causing this? Am I overlooking something obvious or not thinking out of the box enough?
Any help would be appreciated.