Bleeding super duplex part 4.

[Overknasten]

The MBC is reassembled and everything slidies and moves as it is supposed to.
I´m trying to bench bleed it before final installation. I haven´t attached the reservoir just filled the 2 chambers in the MBC body.
Fluid runs out of the front port. I can´t get fluid to run out of the rear port.
If I put fluid in a syringe a press it through the rear chamber inlet port it flows and after doing that I can pump out fluid untill the innner chamber is empty. The problem is that the fluid will not flow freely into the rear chamber.
1. Is this because the fluid level is not high enough, when doing the bleeding without the reservoir?
2. Why on earth is the inlet port from the chamber only 0,5mm.? It doesn´t make sense.
3. Should I try and fill the rear chamber and then apply vacuum on the outlet port to see if I can have a proper fluid connection between the reservoir and the inner chamber?

I know I am close - just missing this last detail.
Attached are the drawing of the BMC[attachment=0]BMC.pdf[/attachment]

[deltalxdoc]

I'm not a Fulvia owner, but looking at the drawing if the rear plunger can't touch the
rear stop screw (11) or if the cup (2) is too 'long' the inlet is closed and no fluid can
reach the rear chamber; check with the older cup if the dimensions are correct.

[Overknasten]

Good point comparing the cups I´ll do that this afternoon.
Really anoying when buying a repair kit that should fit an original BMC. Grrrrrrrrr!

[Huib]

Exactly.

And also there is no hole to the compensation chamber of the rear plunger. If the thing is as on the drawing, it cannot work.

There is more documentation, drawings, manuals etc from the early 70's which are no good. The feeling I often have is that the drawings were made by not fully informed students. Whether it has anything to do with the transition from series 1 to series 2 or from Lancia to Fiat or something else I don't know.

I am not in the workshop now. I will look at an actual pump later.

[Overknasten]

So now I am only confused on a much more informed level......
The odd thing is that it worked all very well in the spring before I started the overhaul.
I have only renewed the sealings in the BMC

[deltalxdoc]

... then the problem can be on wrong kit parts (it's quite normal that some o-ring
or seals in a repair kit is similar but not equal to the installed one,
sometime is better, sometime not ).

[Overknasten]

Took it apart again. The o-rings and sealings are similar and looks exactly like the old ones.
Hain, I agree that a cut through drawing down the center axis of the BMC will not show all and looking at the drawing you are right it wouldn’t work. I have attached 2 pictures of the front and rear chamber where the real fluid ports are shown.
I still can’t figure out what the very small hole in the recessed hole in the rear chamber is used for.
Having said all that everything looks fine but I still can’t understand why the rear outlet port isn’t flowing. [attachment=0]278133E9-9509-4742-9A27-B4588B30437A.jpeg[/attachment][attachment=1]2D72C29B-FDFA-4995-908A-73C44C5A9A2E.jpeg[/attachment]

[Overknasten]

My apologies it should be Huib not Hain - iPhone spell check with out me asking for help. Sorry

[Huib]

Are you talking about the small hole roughly in the center? That hole is just before the cup. It fills the rear chamber. When you operate the rear plunger, the first thing it does is close that hole by moving forward. When the plunger moves home, it opens that hole so fluid can flow back into the container when it expands as the result of temperature rise.

Your problem is most likely with that hole. The plunger must go back completely.

If it does not there may be one cause or a sum of causes.

The copper part not polished polished polished enough.

The O ring inside the housing bad or wrong material. It must be EPDM.

The springs inside the MBC are swapped.

The spring on the pedal is gone or too weak.

The spindle of the brake pedal is partly seized. With nothing attached to the pedal it must swing SMOOTHLY.

The pin on the booster is too long.

No free play on the pedal. You need a bit of free play there.

The nut locking the rod from the servo on the pedal may be too tight. Or too loose.

[Overknasten]

Yes that is the one I am afraid of maybe has corroded a bit so that the fluid cannot pass freely. I have measured the seals and they are same width as the old ones.
I might drill it up to 1mm. I don’t see it should do any damage to functionality.
The rest of the BMC is working as supposed to now that I know where to place the springs👍
I will polish the brass plunger some and finally ask Historic Racing about what material they use in the repair kits