LucianoDrossi

When I press the pedal, I can hear a pissing sound inside somewhere, and I never get any real firm brake. Must be remaining air despite I have bled the system with VCDS. No air bubbles do occur during any bleeding anywhere.

This is the ESP ABS I have, the same as in A4, RS4 and A6 C6.

Sounds like a defect master? I get firm pedal once I have pumped it up, and it stays, no sinking. When I let it go, the brake is too soft again next time.

desertsage

The sound makes me think that your brake booster is leaking (vacuum) but symptoms sound like a master, like you said. Does it feel like you need more pedal pressure to stop, once you get it pumped up?

LucianoDrossi

If the vacuum servo was defect, I would have had a heavy pedal, which I don't have. One truth and concern for me is that the master cylinder now is actually from a non-ESP system, connected to a solely ESP system. These two types differ in fittings, but they might differ in how they work. It now feels like I constantly need to pump up a tension in the system which is gone in two seconds.

desertsage

I looked into this and apparently master cylinders for an ESP system are different than for non-ESP. I think there is a brake pressure sensor in the ESP masters. I'm out of my league here with this question but perhaps you need an ESP master.

LucianoDrossi

They do differ in fittings, where non-ESP has both M12 fittings while ESP has one M10 and one M12. There is no electrical contact which isn’t on the other. I’ve looked carefully.

The hydraulics might be slightly different however, but I think that only the fittings differ, and that my master is blown.

LucianoDrossi

I’ve bought a new master cylinder, really hoping that was the whole cause.

desertsage

I hope so, too. Fingers crossed!

I just bought a new master cylinder (Mayle) for my '96 B5, Blueberry. It has the sinking pedal.

LucianoDrossi

While working with brakes, one press on the pedal beyond the normal brake range can damage the dealings in the master. Regarding the huge work I’ve made with this car (all brakes are new, and break lines except the longitude original aluminum) I should had spent 50 USD more on a new master just being safe. Stupid not doing so.