In RS Centre click SSE, options, controls, filter settings, footbrake, axis.
I have set my brake up like this , Curvature 1 block, Curvature 2 1 block, Rise Rate 6.0, Fall Rate 4.0
Its a matter of trial and error to find what works for your pedals, I have the Basher brake mod installed and found the default settings within the game un-drivable, the slightest touch of brake would lock up the wheels.
Hope this helps