So the mechanic which was working on my car yesterday was busy with another high priority task today. Another mechanic was assigned despite the fact that I was very unhappy about it. However, he promised me to do his best.
The first thing he has done was blocking off one of the port on master cylinder. The one towards the front of the car. Then started the car and checked brake pedal feel. Solid, as he said, I was too tired to go and check myself. I checked which wheels the first MC circuit (which was still attached, the one that is towards the middle of the car on MC) did block. Appears it is Front Left and Rear Right.
At this point I said to myself: Finally I know for sure that the MC is designed to be diagonal and not "frnot" and "rear" between the circuits.
Then the mechanic reconnected the circuit which was blocked at MC. We decided to bleed with ignition off, the classic way "pump, hold, undo the nipple". We did this at least 15 times on FR wheel, approx 10-12 times on the rest. Then we did the bleeding using VCDS way, one wheel per time, repeating about 5 cycles. We were supposed to do both fronts at the same time but you actually need 3 persons for that, however, only the mechanic and me were available. So we did that.
"Well, it's time to start the car and check the pedal feel" he said. He started the car, let it idle and pressed on brakes. "Acceptable" he said.
I want to remind that at this point rear brakes were not touched (calipers and rotors in place) but the front ones were dismantled: rotors were sent for being turned at a shop oppiste the street and the calipers were squeezing thick metal bricks instead of pads to rotors
At this point we started assembling everything back. Meanwhile the rotors were turned. Well, the sad story is that they are almost at their wear limit after turning (19.6 mm actual and 19 mm is the minimum thickness). Installed new set of TRW brake pads. Used Ate Plastilube on pads backplates as well as the rotor surface where it meets wheel bearing (to prevent seizing). Used TRW PFG110 grease for guide pins.
I went for a test drive. I did 5-6 firm and rapid stops from ~55 mph/90 km/h speed during the short testdrive (7-10 min). When I returned back I realised this might have been my mistake. Strange burning smell was felt, front rotors were super hot, rear were hot too. But hey, rear rotors are now shiny! All the rust is gone. They never have been so clean wich the previous master cylinder! Looks like the brakes are functioning better now when the original MC is reinstalled back and brakes bled.
I'm still not 100% satisfied with the pedal feel and biting performance but now I think the brakes are functioning at ~90% of my satisfaction
I wold the workshop owner that I accidently heated up the rotors. He suggested me to be careful next time and don't do that excessive braking as the rotors are nearly at their wear limit. Better be easy on brakes unless actually needed.
Very long story short, looks like the brakes might function better now.
Also, it seems that the replacement master cylinder, which was installed into the car on 2015-Jan till yesterday was somehow "weak" or worn out, causing strange pedal feel as well as lack of braking power at rear wheels.
Thanks everybody for your input, the ideas, suggestions, etc!
All the best!
PS: when we put everything back together, we've realized that that Rear Left caliper must be binding. The wheel is harder to free spin when the car is on lift. This wasn't there a few months back! Must be either sticking guide pins or corroded cylinder. Will order a full rebuild kit (from TRW) or look for a used caliper at the salvage yards.... This is the next task for the spring
