Bad master cylinder?

[eacmen]

With engine off sound happens until pedal firms up. It doesn't happen with light smooth braking, it happens with heavier pedal pressure. I.e) pump the pedal fast a few times.

Smoke test was clean!

Just sounds like the vaccum air in the booster that builds up.

[OldRanger]

Ill add that to the list of things to check. One thing I noticed is that the brake fluid gets unbelievably dirty quickly in the MC reservoir.

Kdubski - what did you ever determine related to that noise you recorded (back in 2021...sorry for digging this up). My system is doing that after some work I did that resulted in an empty reservoir (I added a brake pressure sensor on my MK60 systems). I don't recall that noise prior to the work.

My brakes work OK, but they feel a bit different. A softer pedal and perhaps a bit less max pressure.

[mrgizmo04]

I recently replaced the pressure sensors and tried not to disconnect lines as much as possible...I still had to disconnect a few. Bleeding the air out of abs/dsc was a real pain, I had to do around 5 rounds (via INPA) after driving it a few times. I got most of it out, but first half inch of pedal stroke still feels a bit soft.

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[Kdubski]

Kdubski - what did you ever determine related to that noise you recorded (back in 2021...sorry for digging this up). My system is doing that after some work I did that resulted in an empty reservoir (I added a brake pressure sensor on my MK60 systems). I don't recall that noise prior to the work.

My brakes work OK, but they feel a bit different. A softer pedal and perhaps a bit less max pressure.

I never resolved the issue. I've bled over 8 liters of brake fluid through the system in various ways but ultimately just needed up living with it. Please let us know if you resolve it.

[OldRanger]

I continue to use the car and try to ignore the sound if/when I hear it. Whatever it is, I've learned to compensate for it. A very experienced instructor drove my car with me on track this weekend and had nothing but good things to say about my setup. Data from my aftermarket brake pressure sensor indicates the system is working properly. (I purchased the sensor from Morehead Speedworks, installed myself, with a fluid flush at a local race shop that specializes in BMW)

[Kdubski]

Worth mentioning I replaced a booster and MC in the troubleshooting process. The sound went away for ~60 miles, only to return as I was pulling up to Limerock Park for a track day!