Centering your Navomatic autopilot

[hharney]

Thanks David and nice posting

I haven't digested the whole post yet but will entertain you with my dilemma. My Nav-O-matic 400 will not hold ALT. Based on the user manual it says to center both trim and pitch dials and then turn on the ALT HLD switch. If I do that the airplane takes a dive and the only way I can level the plane is to use the pitch and trim dials. I have the manual trim for level flight before I engage the A/P. So I don't use my ALT HLD. Everything else works about 98%. Any thoughts?