I have the size of the o-rings somewhere. Ill try to find them and post it here.

There are springs, you can see them in the drawing.  But after 40+ years they might not be doing much.  Edit - just saw EuroDat's post.  The drawing shows springs but maybe they don't actually exist.

I read on a Datsun 1200 forum that only USA cars have the switch.  It's one of those safety features that only the US has.  They got rid of it later when they went to the fluid level sensor in the 280ZX.  Apparently us US citizens are forgetful idiots who don't know how to maintain their vehicle's and will let the fluid level drop so far that the brakes stop working correctly.

Edited September 23, 20213 yr by Zed Head

Ok, found it.

You need EPDM rubber for brakes systems.

 

In the first post Seppi72 shows a photo of the later type. They don't have springs.

Something I have not tried, but know people that have done it.

You can cut a thread in the cone section with an M3 tap, I believe, and use a M3 screw to pull it out with a claw hammer for example.

The flare on the pipe is large enough that the thread will not effect its sealing. Like I said, never done it, but know of two peolle that have done it with no issues.

 

1 hour ago, EuroDat said:

In the first post Seppi72 shows a photo of the later type. They don't have springs.

Actually his first post shows springs.  I was going to dig up a 72 drawing but figured the OP's own post was good enough, I assumed it was a 72.  Just saying...

John Coffey used to chime in to these types of threads about having to reset the plunger after the switch was actuated.  Maybe Nissan put springs in later to fix that problem.

 

Or maybe they took them out later.  Here is 76 below.  I looked at 70 also and it shows springs. 

22 hours ago, Seppi72 said:

In reassembling my, now, 50-year-old, early '72, HLS30-46372, build date 9/71, I've run across an issue with this device, which is supposed to warn if there is a significant pressure differential between the front and rear brakes.  I cleaned up the part and noted that while I can see daylight looking into the front brake line inlet (air will easily flow in that port and then out the other two front brake line ports), I cannot see daylight looking into the rear inlet port.

I don’t know if there’s simply gunk clogging the channel or whether there’s something more substantial blocking it (the piston?).  To compound my problem, my device looks nothing like the illustration shown in my 1972 FSM.

 

I was referring to the photo, but see now that he also posted a photo out of the fsm for the early type.

If they start to clog up they can be a pita to reset. I think they may have removed the springs to stop the switch resetting before you fixed the problem. The springs would reset the switch when you released the brake pedal.

Mine activates when I bleed the brakes, but resets after and I press the pedal down a thew times.

If you can't get it to reset after repairing/replacing the faulty component, you can open a bleeder on the other section of the braking system, then slowly press the pedal down until the switch resets. Then colse the bleeder.

 

I'll give EuroDat's heat and tap procedure a try.  And, I don't know where he got those O-ring specifications, but thanks.

After sitting in Kroil for the better part of four days, EuroDat's "heat it and beat it" method worked to dislodge the piston in my switch.  About 40-60 seconds of heating with a propane torch along both sides of the main chamber axis and then tapping it hard on the flat of my bench vise did the trick.  Thanks, buddy.

Edited September 27, 20213 yr by Seppi72
Adding details

Super!

Post up some rebuild results and tie this off nicely