After checking by a professional, it turns out that my brake booster needs to be changed. Given the difficulty in getting it repaired or buying one in Europe and the cost and given that I replaced the original rear calipers with 4-piston Brembos, I decided to remove the Mastervac and install a system with double master cylinder and mechanical distributor between front and rear. I also removed the shuttle valve which was no longer working correctly and is of no use from my point of view (if there is a brake problem you can notice it without needing a warning light for that).
I bought two master cylinders and the distributor for less than €150 and I made the support.
I now have a hard pedal and it brakes quite well but you have to press quite hard on the pedal which is normal with the removal of the Mastervac. To reduce the effort on the pedal, I ordered a set of Porterfield R4-S front pads for which I read very good reviews on the forum. However, I have a question, what is the coefficient of friction of these pads? I couldn't find the answer on the Porterfield site?
