2013 X5 3.5i 90k miles. I did a cooling system maintenance. Water pump, thermostat, belt, idlers, tensioner and expansion tank. While I was doing this I noticed the front right caliper was partially seized. Couldn’t rotate the tire when jacked up. I pulled the caliper and took it apart to find the piston was badly corroded and pitted. So I ordered two front calipers and replaced them. After bleeding the pedal seems hard until I start the car and then the pedal goes slowly to the floor. Can’t find any leaks and the fluid level in the reservoir doesn’t go down that I can see. So I figure it’s the master cylinder. Ordered a new one, put it in, bled it and it’s doing the same thing. I got ISTA-D running and ran the bleed procedure on all four wheels. No difference. Pedal is rock hard until car is started and then goes slowly to the floor. Car has been on jack stands for over two weeks for a simple caliper change. Please help if you know what is going on here.
Did you use a pressure bleeder or the old fashion way? I would strongly recommend a pressure bleeder. Re-bleed all 4 wheels starting with the rear passenger side then while still under pressurized use ISTA to bleed the ABS. It isn't that uncommon for the brakes to be soft at first. If you take it out around the block in the neighborhood it should build up pressure.
