Running 2 drivers on the same axis

I’m running mach3 have two drivers running two motors on my Y axis. They are wired in to my Bob board. One driver runs to the A port on my Bob board, the other driver runs to my Y port on my Bob bored. I configured mach3 to recognize my x,z,y, and A drivers. I went to slave, master, and under the Y access an assigned A as my slave. Went back to configuration and checked the box as slave as master. When I run my machine, each driver works independent of each other and not in sync with each other. How do I run my a driver and why driver sync