I had replaced my RV-10 TruTrak roll servo on 30 Oct 2019 with a refurbished roll servo from TruTrak, after my original roll servo failed.
Less than a year later, my roll servo failed on 7 Aug in flight.
Following the TruTrak sale to Bendix King, technical support/repair seems to have been outsourced to Mid Continent Instruments and Avionics (mcico.com). I called Mid Continent at 316-630-0101 (also 800-821-1212), http://mcico.com
. I spoke to Bruce, their Trutrak guy.
Bruce told me Mid Continent has the BS-C servo for $500 (not a bad price, IMO). I would need to work with Andrew (former Trutrak owner, still with BK) regarding warranty coverage. But Bruce suggested I probably have a broken roll pin inside the servo (not the shear screw). He suggested I could replace the roll pin, which would get my autopilot back in operation for an upcoming 10 hour IFR flight. I agreed, I paid for rush shipping of the roll pins.
Open up, per Bruce: 4 hex head screws come out to pull the stepper motor off. I looked inside, saw the roll pin was still intact, but had backed out of the gear. Bruce said use new one, don’t re-use, to get better fit (seems wise, since the existing pin backed out in less than a year).
Be aware Torx screwdriver TT8 bit is required to open servo gear area to get to the gear and roll pin. I opened that, removed roll pin (intact). The roll pin I need is 3/32”x5/8”. Bruce says to use some sort of thread locker (not permanent) on torx and hex screws upon reassembly.
Safety note: If the TruTrak BS-C servo internal roll pin shears or backs out (mine has done this twice), the spindle and control arm can fall right out of the servo housing, with the risk of jamming controls.
On my RV-10, the servo link is installed with the shoulder washers TruTrak recommended. Those large shoulder washers apply just enough force to keep the broken spindle and control arm from falling out of the servo. I added a trapping mechanism to capture the pitch servo spindle/torque enhancer if it should happen to similarly fail. In addition, my checklist includes the warning that if any autopilot component malfunctions I should completely turn off the autopilot and investigate before further flight.