More troubles with new master cylinder

Another issue to check, and I know this from personal experience, make sure that little rubber ring on the brake rod is fully inserted into the end of the master cylinder piston. I thought mine was but it was only partially inserted making my brake pedal look normal but holding the piston in just enough to keep pressure on the rear brakes. I had to pull the MC and used KY Jelly on the rubber (no pun intended) and it slipped right in (that's what she said)!