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Down to what seems to be the last major order of business - occasionally when coming to a complete stop, the pedal will feel like it’s popping or bubbling. Hard to explain, as the pedal otherwise feels fine. It almost feels like what you’d imagine it might feel like if the pads were hitting speed bumps or potholes on the rotor. Pads and rotors were checked and are good. Not sure if that counts as spongy, and I can’t seem to hear or feel it in the way the car stops. This happens only when coming to a near complete stop, under 5-8mph, and doesn’t happen every time. 

With the car off, I can get 15(+/-1) pumps of the pedal before it goes rock solid. 

Brake lines at the calipers all look good, aren’t leaking, or cracking. 

I do have fluid here, which realoem says it a voltage regulator? Hard to tell where exactly it’s weeping from, or if it’s actively weeping at all.
 

there is also light fluid here, at the PS pump, but it’s not from dripping done the hose.

 

Brake fluid and PS levels look good, and I don’t seem to have any peculiarities in the power steering performance.  Also, no drips on the driveway ever. Brake pads and rotors and calipers are good, and perform well during “spirited” driving.

I’d love to keep the current setup rather than converting to a traditional vacuum booster, it at all possible to do so.   Hopefully this is a fairly simple fix?
 

Sounds like an ABS failure to me.

stuartinmn wrote: Mar 24, 2025 7:11 AM Sounds like an ABS failure to me.

Air in the brake lines??...did you bleed the circuit??...that is easy and cheap. Then check the brakes rubber hoses in every corner, then the Master Cylinder and Brake Booster. When pedal is depressed 15 times the ATF level is 1/4 inches to the top??....lastly the "bomb", the baloon inside could be hard or broken

stuartinmn wrote: Mar 24, 2025 7:11 AM Sounds like an ABS failure to me.

When I've had false ABS activations when coming to a stop its usually been rust in the tone rings, or if the gap between the sensor and tone ring is adjustable, having that too large will do it too.  Basically the ABS system loses pulse when the wheel is barely rolling and it triggers the antilock stuff.  I don't know the BMW system specifically but early ABS tends to have a lot of similarities. 

 

gadget73 wrote: Mar 26, 2025 8:32 AM When I've had false ABS activations when coming to a stop its usually been rust in the tone rings, or if the gap between the sensor and tone ring is adjustable, having that too large will do it too.  Basically the ABS system loses pulse when the wheel is barely rolling and it triggers the antilock stuff.  I don't know the BMW system specifically but early ABS tends to have a lot of similarities.