1970 350 cu. in. convertible brakes, on-going problems

About the end of March I asked this group about the brakes on my 1970 350 cu in. 350 hp. convertible. The consensus was new callipers.
I got new back callipers and all the parking brake bits and that is
all OK, but before bleeding the rear and replacing the front, I decided to blow out all the old fluid from the master cylinder and the pipes. I took off the master cylinder, cleaned and re-sealed it and assembled it with new 4 dot fluid.
I tried to blow out the pipe to the rear with the rear callipers disconnected, but the pipe seemed blocked. The brakes were working OK before. I tried sucking with a vacuum supply, but that did not work either. So I filled up the master cylinder reservoirs with new fluid and tried to pump it through. Apart from a couple of tiny bubbles coming out, the fluid did not seem to be going into the cylinder. The brake pedal was not building up pressure. So why is this, I have left it for the night and maybe it needs some fluid to seep through to allow the pumping action to take place?
Has anyone got any ideas as to why this should be. I also would like to know what the small (broken) switch is that sits between the two vacuum overrides for the headlights and the wiper flap, under the steering column. Where do the vac. pipes from these two vac. taps go to in the engine compartment? I need to trace out where I am losing the vac to these two circuits.
Thanks for any comments; they will be most welcome, if anyone knows.
Regards George.
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The brake lines from the master cylinder generally go into a metering block (has the brake warning light switch if the rear and front brake systems have a large difference in pressure between them). This block may have valves that do not flow fluid unless the pressure is a particular positive value. This prevents vacuum in the lines that could suck in air or water. You need full brake pressure to get fluid through here or blow fluid through the system after this metering block.
The switch below the steering column is to turn off the wiper blades. I hope I am remembering correctly, but the blades will not operate unless the vacuum operated door is open. This prevents major damage if the blades were to operate with the door closed. Once the door opens, there is a switch near the firewall on the engine side that powers the wipers. In case there is a vacuum problem, the wipers may not turn off. This is what the under steering column switch does.
Vito

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Some issues you might have to do with the brakes.
- New calipers will eventually do like the old brakes, as the cast iron pits form moisture buildup due to lack of use and then they leak. Stainless steel sleeved brake calipers work better.
- Master cylinders often need to be bench bled. The rebuild kit has instructions for this. Basically, you take a hose from the output port and stick the other end in the reservoir so that as you pump the MC, it blows bubbles in the reservoir. When the bubbles quit, it is bled.
- Set up of the master cylinder plunger is critical. There is a threaded adjustment that allows you to place where the plunger fits in the MC before it depresses the piston. It must NOT depress it when you are at rest with the pedal.
- Blowing through the lines is often not possible since you have a proportioning valve in the lines. These are not true proportioning valves in that they regulate the pressure to the rear, but rather a balance system so that if you lose pressure on one circuit, a piston slides and closes that circuit so that pressure stays on the other. When you applied pressure to one circuit only (rear), you may have closed this valve and thus nothing flows. Some valves will reset but others have to be reset manually. I do not know what your car has.
The switch under the steering column between the headlight and wiper override switches is the parking switch for parking the wipers in the up position for changing wiper blades.

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Thank you very much indeed for two very useful and clear replies, You have saved me hours of investigation - I am sure.
I had a bag of new brake cylinder parts, but no instructions.
Trying to switch off the power to the wipers as they came up out of the parking area was starting to get up my nose! Now if I can only find the other end of those vacuum hoses!!!
Thanks and regards. George. (in uk.)
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My optimism was a bit premature! I think I had better have a look at the master cylinder rebuild and bleeding instructions. I have got brake fluid everywhere and still not managed to make it go through the pipes, by feeding the pipe outlet back into the reservoir. The only way I can see to assemble it full of fluid, is to do it in a bucket and that would take all my nice new paint off the housing. Plus it would waste a stack of fluid. Does anyone have a copy of the instructions. Please.
I have decided that the root cause of all my vacuum problems are the two headlamp actuator relays, - they are both leaking vacuum internally from the vacuum feed inlet. I cannot see any way to repair these and I have ordered two more. This is where my vacuum has been going since the word go. Mice biting the pipe in the wiper park detection area did not help.
After getting a new seal for the wiper door actuator this circuit works ok and the headlamps will pop up and down if I feed vacuum directly to the actuators. Lifting off the bonnet - hood (?) (on my own) was "interesting" I had to rig up ropes all over the place.
Thanks and regards, George.
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