I am a Giores. My parents divorced when I was a small child and I had an on-off relationship with my father throughout my childhood. He didn't have much to do with me. After I converted and before I got married I told him I had converted and was getting married soon. He told me that he didn't think it was the right thing to do. I haven't spoken to him since (this was many years ago). I've read that a Ger is supposed to honor their parents with Derech Eretz and gratitude. Do I need to do anything about this estrangement from my biological father? I don't want to, but if I am obligated to, then I will.
The Rambam (5, 11) writes that converts should honor their parents, but, as is the case regarding gentile commandments in general, it isn't exactly like one of the 613 commandments regarding the extensive honor that Jews are obligated towards their parents. R. Moshe Feinstein (2, 130) explains that even a convert, who is considered as if he has been "born anew", must still show gratitude and recognize all that his parents did for him, and surely we don't want people to say or think that you are "less nice" since your conversion. Rav Kook (Da'at Kohen 148) adds that this is common decency. On the other hand, we also don't want such a relationship to have a negative influence on your decision to be an observant Jew. Accordingly, at the present, where it sounds like your father isn't interested in such a relationship, as was the case even before your conversion, than you aren't obligated to search for him. But should your father call and want to renew his relationship with you, and requests your honor or help, than surely you must oblige to the extent that it doesn't mar your religiosity, nor harm your marriage.