Brake Bleeding question

LarE9

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I recently picked up '71 2800/Bavaria that had been sitting in a garage, not driven for 20 years. I rebuilt the whole brake system - rebuilt all calipers (rear disk brakes), and used PMB Performance for reference, among other sites. I installed new hoses, new master cylinder (2nd new one), cleaned out pressure regulator valve, unclogged a couple hard lines, and got all the old fluid and debris flushed out. Following the factory guidance on bleeding procedures, I bled using the 2-person manual method, vacuum method, and lastly a pressure bleeder, so now I have a steady flow of clean and air-free fluid at all calipers. Probably put 1/2 gallon of fluid through the system, and yet, my pedal is still very soft. I have a '72 E9, so have some experience with these brakes, and know sometimes it takes a while to bleed, but this seems excessive.

Has anyone else had a similar experience? Could air STILL be trapped in the system somehow? Or is it something else? Any suggestions on a path forward? (i.e. keep on bleeding?) I researched this a bunch, but not sure how to troubleshoot at this point.
Thanks!
Larry
 

LarE9

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I hope so - inner, outer, then top. However, the blue shop manual I have shows the top as "A", inner as "B", and finally outer as "C". It has a note saying "...always bleed lower piston "B" before lower piston "C" (which I did). Since they noted that, rather than saying do them in exact order A, B, C, I made the assumption that those are the only two that have to be in a specific order and therefore may not make a difference if the top is done before or after these two lower ones. Hope that makes sense. How do you guys do it? (I have read some conflicting things on this).
 

LarE9

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I put a new one in I had lying around that I inherited from my E9 previous owner, but turns out that had issues, so I ordered a brand new one from Autohaus. I could tell right away that this new one was working compared to the old new one. I was also thinking about bleeding it, so I did a pseudo bench bleeding by filling it and pumping it while it was out of the car. When I reinstalled it, of course it was not totally full at that point, but I tried my best to get any air to coming out through the top by tapping it as I was filling it (before putting the reservoir back on). I kept tapping until all air bubbles went away, as I could see them through the plastic hose connectors. I know a lot of people swear by bench bleeding and have their methods, but I spoke to two different seasoned BMW mechanics (with lots of experience on these older brake systems) and they don't bench bleed at all (due to time), and never have issues. So maybe the master is something I should pay some attention to? I am going to try some more bleeding today and will report back. Thanks!
 

Stevehose

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I've never had to bench bleed either, perhaps some gravity bleeding might help, open up each bleed screw a caliper at a time and let it drip out for a while, topping off as necessary to keep the level above the clutch tube.
 

LarE9

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Thanks Steve. I think I will do another round of pressure bleeding, then will try gravity if that doesn't work. If both unsuccessful, I will probably just bleed a bottle of beer or two the old fashioned method - via gravity into my mouth. :)
 
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