I have been messing about with these brakes for months on and off. I postede in May time about the difficulty of getting fluid through to the back calipers. See here:
Four new calipers, the complete set of bits to do the handbrake, new pipes, new pads, lots of odds and ends and so much time that my head spins just thinking about it.
I thought it must be the pressure differential sensing valve, but I took it out and pushed the spool back and forth against the springs and the contact made at the appropriate time AND air could get through both ways, i.e. front and rear when it was at rest. I tried bleeding the front brakes with a vacuum pipe on the caliper bleeding nipples. I made up a special bleed nipple that did not seal but let fluid through all the time. With a big reservoir above the master cylinder and a glass jug between the nipple and my vacuum pump, everything looked fine and I got lots of clear fluid going through. This should have not actuated the pressure valve at all.
However when I tried the same on the rear calipers, it was as if the valve had sealed again, as no fluid could be sucked through. It was too late to do any more, today, but what do you think about that? As far as I know there is nothing else that could stop the flow. Or could it even be the set up of the master cylinder clearances. It WAS working and when I took it all apart it looked in perfect condition so I put it all back as it was. Cleaned out with new DOT 4 fluid, of course.
I am glad to say the lights and wipers and associated vacuum circuits are working perfectly now too. I have not really got that much more to do.
This car has got to go out of my workshop very soon as I want to build a bio-diesel processor exactly where it is now. I has been jacked up for months.
Anyone got any ideas? Please. Regards George.