It's like this:


When you apply force to brake pedal, both the firewall and the brake booster body flex.
This is more noticeable in a FD but the FC does it to a lesser extent. The bracket (here bolted into existing holes in the strut tower, it's the same on a FC) helps minimize this "flex", ensuring that the force you apply at the pedal makes it to the calipers.

 

Oh, I didn't knew that.
Does that happen to all cars, or is it a problem inherent to the RX-7?

 

I don't think it's much of an issue in the FC, it's built like a tank compared to the tissue thin FD.
With a FD you can see the MC move when the brake is applied.

It's simple enough to make though (there are much fancier versions available) and can't do any harm, so go crazy.

 

Yeah the master cylinder in these cars do move when applying the brake. It was doing it when I had my bud helping me bleed them and when I was looking at how much it was flexing I knew something had to be done. I think the FC coupe chassi is 3 ply aluminum and the Vert is 5 ply, making the firewall on the verts a little more stronger, but still.

Clokker, is that your car?

 

It was a project I was heavily involved with.

 

Thanks for the info.

 

So I was looking at my master cylinder today to make a anti-flex bracket. And I figured from everything I learned in my engineering class in high school I can come up with SOMETHING other than pushing on the front of the cylinder. It would be better to mount it to the base of the unit so I did this with a piece of scrap thinking it may or may not help slightly. And after driving, wow. Huge difference. So with this in addition to the cylinder brace that pivots on the front it should be pretty rock solid!

Bracket only took 20 - 30 mins to make too!

 

That looks like a good idea.
Nice