I was taken apart one of my broken master cylinders and i noticed the primary intake doesnt't have an equalization port like the secondary has instead it has a hole going through the primary piston. I'm curious on how this would work because it seems like when the primary piston starts to compress the fluid the fluid would just go through the hole and back into the resivoir?

 

service highlights (see the sticky thread) is your friend:

 

Dang i should of checked this sooner i just ordered a 929 cylinder, the little valve in the middle of the piston got stuck on mine and a little tap fixed it.