To get mine to work on my savage X without causing the slide on the servo horn to bind on the wire, I had to bend the wire going into the brake pivot rod. I bent the wire so it was almost perpendicular to the ground when it was almost applying brake. Then I'd put 2 collars on the wire by the servo horn, one that would push the brake wire back when applying throttle and the other to adjust when it pulled the brake forward to apply it (along with a bit of fuel like to soften it a bit). Without bending the wire, the wire would sit at a 60 degree angle forward before applying brake and go further when brake was applied, but it would hang in the slide and apply brake too early due to the angle. After bending, it would sit at 80 degree angle and locking the tires at 65 degrees.
Not sure why though. I had the dual pink disks on it at first, the wire was straight and worked fine. I put some FullForceRC carbon fiber disks on it that I believe were a bit thicker and then had to bend the wire to get it aligned well.
With the pink disks:
Brake linkage:
What I put on it when those died:
Brake linkage with the bent wire: