just wondering what its there for.. is it a bleed to adjust when they open?

 

it holds a small plate that hold the actuator shafts in place. It does not allow you to remove the sleeves or adjust anything. I'll look at my car tonight to try and remember exactly what the screw looks like

 

It may be a stop for the actuator travel, I remember playing with mine a long time ago, and it didn't seem to "tweak" actuation pressures any. If the gaskets are good, not much if any air should be "bleeding" off...

 

I looked at an extra set that I have... they are a "pre-load" adjustment for an internal spring on the diaphram.