Master cylinder not putting fluid out for main front circuit

[droptop]

To make a long story short, I rebuilt a Beta master cylinder today and attempted to bench bleed it prior to fitting.
The rear chamber for the dual circuit is firing fluid a couple of metres when I depress the plunger but the front only produces a small squirt, followed by a lesser one and then nothing whilst the rear continues unabated.
Does it need to be plumbed in to create back pressure?
The cylinder itself if sound and free from scoring and prior to disassembling the pistons and removing the seals, I photographed the untouched assemblies and also checked the diagram in the Haynes manual.
I also dismantled another m/c with broken mounting lugs for comparison.
I've dismantled, cleaned and reassembled the thing three times this afternoon and have achieved nothing. The seals are of a ring design so they can't be flipped during assembly unlike other types so that's not the issue and it was assembled wet as it should be
Any suggestions what I'm missing?

[lukasdeopalenica]

Hi,
It depends actually what do you mean by the rear chamber? Looking from the servo and actuator side the first plunger is depressed first during braking and feeds two circuits (front and rear calipers), then if you depress the brake pedal further the second plunger starts moving and pumps fluid to the third circuit (front calipers). The first and the second plunger do not move synchnonically, as they are connected by a spring, and the plungers (pistons) have different surface area so force different flow. Maybe that is the reason of the situation you are facing. Check by hand if the second plunger is being actuated in the final stage of the actuator move.

[droptop]

I've been pumping it by hand and the front circuit plunger is moving but I wonder if the cylinder needs to be fitted to the car so actual hydraulic pressure from the rear plunger moves the forward plunger?
Surely the return spring alone is insufficient to produce sufficient pressure in the circuit to operate the pistons?
I'm going to try it on the car today and bleed the lines at the wheels from o/s rear to n/s front and see.
There's no physical reason I can see other than the inability of a spring to actuate a caliper piston

[lukasdeopalenica]

I think that the spring creates just the tension and the actual movement is realised when the first plunger reaches the second one and then move together.

[HFStuart]

Block off the outlets or the rear chamber temporarily and then try again. I suspect that load isn't being transferred to the front part as there's no system pressure.

[droptop]

Block off the outlets or the rear chamber temporarily and then try again. I suspect that load isn't being transferred to the front part as there's no system pressure.

I tried that without any real pressure being present at the front outlet so I gave up, binned it and used the one from my donor coupe without doing anything more than draining all the old fluid out of it and flushing it with new stuff before mounting it.
I wasted hours messing with the other cylinder simply because I hate giving in and it cost me a seal kit and a day's work in the process.
Still, looking forward, I'll soon have the '79 spider on the road and seeking a new home which hopefully will be the residence of an enthusiastic and competent welder as I think the car is far too good th break for parts but who knows? Stranger things have happened