Calibrate Joystick B

I'm trying to setup the vertical axis of joystick B as my brake.
But GP3 will only calibrate joystick A.
FYI: I'm using an Classic Xbox controller with the XBCD driver on Windows XP.

I´m using a F710-gamepad and think thats similar to what you use. Here my opinion:
left joystick for steering - right for acceleration and braking
(should work)

I've not been clear enough. I want to use seperate Y axis for throttle and brake. This way it's possible to brake and throttle at the same time. At the moment I've mapped the Y axis of Joystick A to the left and right trigger of the controller and although this works they cancel each other out when pressed at same time. Using the second Y axis of Joystick B for braking will fix this problem but I can't get it calibrated.
Another question: Can I get GP3 to support the Z axis or slider? Lots of joysticks have a Z axis and I could map that to the left trigger for braking.