I changed the two rotors out with one 13" floating rotor and 6 piston caliper on my 2009 Street Glide. Did I miss something? Did I need to change the master cylinder to a different bore size?

The front brake is hard to pull and seems to not stop smoothly with some vibration. I sent the rotor back to RC Components and they sent me a new rotor, but same issue.

Any suggestions?

 

You are right about the master cylinder. I am sure I have read about some people doing the same as you and getting along fine, but Harley make two versions of the master cylinder, one for single brake, the other larger in diameter for duals. The look the same on the outside.

I have dual 13" rotors and 6-pot calipers on a stock dual master cylinder, which is fine! See sig pic.

 

I got a hold of Hawg Halters (6 piston caliper) and they said that 2008 and newer you don't have to change master cylinder.