(Also see my reply to cdu above)

Sorry, I only read the head title and didn't notice your car was an 1800 but the conversion procedure should be somewhat similar anyway. Cdu reminded of the simple dual circuit system used at least on some 1968 cars and this would be a much easier modification because of reasons described in that reply. That system used the old front caliper setup and only added one pressure regulator (brake valve) in the single rear wheel circuit, mounted under the car.

Unfortunately, the 1800 brake system changes were many and difficult to overlook:

1: single circuit system. No pressure regulator. One style rear wheel cylinders until ch nr 6979, another from nr 16500 and a third used sporadically together with the two others in between. Front calipers also appear in three different versions. Cars with ch nr 12394-12396, 12418-12435 and 12437- on have the latest style, used also in the dual circuit B18 systems.

2: dual circuit system on B18 cars until ch nr 28299. New main cylinder, pressure regulator added, new style rear wheel cylinders again, brake light switch mecahnical instead of hydraulic, differential pressure (failure warning) valve introduced

3: dual circuit system on B20 cars, ch nr 28300-30000. diagonal instead of axle split, new style pressure regulators (one regulator in each rear wheel circuit), new style wheel cylinders again, new style brake booster/main cylinder (main cylinder mounted on booster instead of separately) and of course new style (four pot) calipers.

4: dual circuit system on B20 cars from ch nr 30001. This includes all ES cars. Discs instead of drum brakes (rear), new pressure regulators. Again...

New style doesn't have to mean more than slight changes and a new part nr. Rear wheel cylinder diameters however were changed at least two times to match new main cylinder setups and thats also why the pressure regulators were changed (new calibration). I don't think those combinations are t-h-a-t important but of course original setups would be preferrable.

Take your time and decide what stage you want to reach. A simple dual circuit system like the B18 setup or the latest evolution B20, diagonal split setup? Did you get your new main cylinder out of a B18 car with the separate brake booster or is it the combined B20 car unit?

I think this is just about all the help I can provide, 1800 isn't really my division. But feel free to ask, of course.

/Martin
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'65 121, '73 165