It's no secret that many cars including Miatas have some flex in the master cylinder area during braking events. Here is a quick viddie I made indicating the amount and direction of the bending issue. You could hook up dial indicators and pedal force and hydraulic pressure sensors, however I was satisfied just getting a sense of the issue at first.

http://www.youtube.com/watch?v=dgd7tvCDUdc

There are a number of ways to address such flaws. The reward is a firmer brake pedal with an increased ability to modulate. Improve a few things like this here and there and before you know it your brakes will be more effective during performance driving maneuvers. Yes this too is datalogging, hated by so many ricers, LOL.

 

Here is another view…was dark so the viddie is a bit grainy…but you can see the important stuff and root cause.

http://www.youtube.com/watch?v=cKnEx0Y2ZZc

 

Ebay Brace fail: http://www.youtube.com/watch?v=7Dm33SrrDiA

 

Here is a strengthened brace…mostly the vertical issue now concerns me with this strategy…other approaches may bear fruit.

http://www.youtube.com/watch?v=GfpPNO9XS_M

 

Here is the main source of flex. It's *not* the firewall.

http://www.youtube.com/watch?v=uhoGOfpUWDQ