[cessnadriver]

YankeeClipper.
I just spent about a year getting my 1965 straight 400 auto pilot operational. The avionics shop I used is Mayday in Grand Rapids Michigan, I had originally wanted to use Auto pilot Central, in Oklahoma. They told me they where no longer working on 400 auto pilots. Mayday rebuilt the computer, and bench checked the servos, and the control head, they told me the servos, computer, and control heads ARE ALL DIFFERENT PART NUMBERS EACH MANUFACTURE YEARS, AND YOU CANNOT UP GRADE 400 TO A 400A OR 400B! I had bad servos. I was very lucky to find a caring SOAPA member who had replaced his 400 to something newer and GAVE me his 400-FREE, I paid the shipping. By chance his servos were the correct part numbers and where in good condition which I used. All in I have about $10000 in, parts, maintenance, Avfuel traveling two times to Michigan, hotels, car rentals, to get my 400 auto pilot up and running. I figured that's much better than spending $30-40000 for a newer auto pilot, for an airplane I bought for $22,500!!
Hope this helps.
Regards, BILLS
'65 C337, Owner, pilot, and A&P