find my biological grandfather

I’ve never met either one of my biological grandfathers. Two years ago, I found out that my father’s father died. He was living with his second wife and two other kids. I didn’t even know that he had other children. I never got the chance to meet him, and I’ve always wondered what it would have been like. There must have a been a reason that I didn’t know him though right? Did something happen between my dad and his dad? But now I’ll never know who he was…My mom’s dad, lives only 30 minutes from my house. I’ve driven by it but have never got enough courage to knock on the door. It’s weird. I’ve been thinking about this a lot lately. I used to not care, because if he cared, he would find me. He has never put any effort to know me. That’s why it’s so hard for me to see him. Any advice???