Datsun Roadster Forum-311s.org

This is a break splitter for a 68. Is there a plunger in the centre of this thing that is supposed to move? If so what's the best method for freeing it if it seems to be seized?

It's the brake safety switch there is a sliding piston about the length of it it's main function after telling you the brake system needs attention
...duh one side has a leak below it
Is to shut off that leaking side to save the fluid
It should center its self unless it is corroded up the cyl ...it why pushing hard on the brakes when bleeding is not recommend
The center thread is for the switch it has a narrow er area , in the center

So to my question then, yes there's a piston that should move in there. Any thoughts on how to get one unstuck?

Yes it floats has springs to center it it is very close tolerance put pressure to one side then the other see if it moves back
If not, you were to replace the assy.
This valve was very important in the? 40s, 50s to
70s when you had 1B fluid tank , not so much after then ,it could be taken out
Our old instructor in votec called it the idiot valve
Explaining that years ago the first car many bought was a well used / worn out ride that leaked fuilds and they didn't do much work to fix it including brake work a seepage leak could drain the tank then disaster