Quote:
Originally Posted by Duckengine
Hello all. Time to flush the Brake system and put in some new fluid. Driver rear bleed screw frozen and then broke. Tried to get it out on the bench to no avail and so bought a new caliper. Put it all back together and then using a pressure bleeder, bled all four calipers with 500 ml of new fluid. First go with pressure bleeder was air pressure only (no fluid) at about 12 psig. Took the car out for a spin and virtually no pressure but I could pump it and build pressure enough to lock up the brakes. Try bleeding again with same method as previous and a slight improvement but not much. Tried again a third time with traditional pump brake process. No improvement. Tried again with the pressure bleeder but used fluid in the pressure bleeder instead of just air as done the two previous attempts. Flushed almost an entire liter through the calipers but still have little pressure on the pedal and need to pump it to get pressure which is firm and can lock up (activate ABS) the brakes. I'm about to give up and take it in but thought I would reach out to see if there are any obvious steps or considerations I am missing. I have read this entire post and others and I'm convinced I am not doing it wrong but I do think I am missing a step not specifically described as it relates to my e92 M3. TIA to all those that reply.
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I think somehow you got air in the system. You have DCT so no clutch to bleed or worry about. You may need to run through INPA or take it to an indy to pulse the ABS system.
Typically I find, right after a brake flush, you need to start the car and press on the brakes and top off fluid prior, during, and after.
Assuming you went furthest from master cylinder to front, everything you did sounds correct however, the output of your effort points to air in the system.
Since the air/gas is MORE (thanks admranger!) compressible than the fluid, it would make sense that you can eventually build up pressure.
There COULD be some other issue causing your symptom like a leaking master cylinder. The caliper you replaced could also still have air in it since it was new.