I am recently (last few weeks) noticing some symptoms which I can not fully explain. I hope that I can get some help here. It relates to my "Japanese SPI" Mini. Earlier this year (Feb ~ April) I replaced the brake components near all wheels: new hoses, refurbished the calipers, new rotors, new rear slave cylinders and new brake shoes. The brake master (GMC90376) and brake servo (GSM119) appeared to be good so I did not replace these. The vacuum hose with integrated non-return valve looked not so good, so I replaced it with new hose and a separate non-return valve (17H2646). Adjusted the hand brake cables at the rear wheels. Then filled the system with new brake fluid and did a proper bleeding procedure. This resulted in proper brake function.
What I am noticing lately is a difference in behaviour between a "firm step your foot on the pedal" and a "gentle touch on the pedal". With the engine off the effect is the same in both cases: the pedal travel is short and results in firm pressure (can't push any further). When the engine is running I notice a difference in behaviour: when I step firmly on the pedal it behaves the same as when the engine is off: the pedal travels only a short distance and then can not be pushed any further. However, if I push the pedal gently, or use one finger to push the pedal, I can push the pedal down all the way to the floor.
I can't really explain what is causing this effect? The difference between engine running and engine off is the presence/absence of vacuum to the brake servo. But, if there is a vacuum leak I would expect the pedal to, eventually, go to the floor in all cases. Thus also when I push hard on the pedal. This isn't happening. Alternatively, if a seal in the brake master would be leaking I would assume that I would observe the same behaviour both with engine off, and with running engine.
What am I overlooking? What could be a possible root cause for this behaviour?
