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  #21  
Old 02-01-2020, 02:37 PM
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Quote:
Originally Posted by StephenVA View Post
The System does not work that way. The way to think of ABS BLock is the think of a passageway with doors that close based on wheel sensor info. Locked up = close door for x mil sec and then reopen. A pulse to the line pressure to release the locked wheel.
Fluid flows all the time through the block on pedal activation.
A normal bleeding process without allowing air to get into the ABS block is the RIGHT PROCESS!
It makes the brake bleeding process as simple as this:
pressurized system, open bleeder screw, when clear flows move to next wheel. 30 mins you are done. Takes longer to get everything set up and to clean up the tools.
??? - in post #6 you list an extensive procedure and here you confirm that a very simple process is correct.

??? - On how ABS works ... my belief (and yes, it may be based on partially ancient technology) is that these systems are typically actuated with hydraulic valves, with brake fluid as the hydraulic fluid, with that fluid mixing with the rest of the brake system when it flows, which happens only when ABS is activated (or when controlled by Foxwell, etc.).

And on the closing doors analogy - I believe a major factor/challenge in ABS is that you don't just need to stop the brake pressure path from the pedal to the brake pad (which closing the door would do), you also need to relieve the pressure already in the calipers. So it is not as simple as closing a door, and that the various systems have a central part of their design being something that relieves this pressure. Otherwise if you were to lock the brake and close the door, you would be freezing the brake in a locked-up state, which of course is the opposite of what you want. So you have to close the door, but you also need to reduce pressure from what is on the other side of the door.

However they accomplish this, I believe there are invariably hydraulic paths in there that contain brake fluid. Since my brake fluid is always "good" without significant age/bubbles/dirt/water in it, my rationale is to accept that a small fraction will not be flushed, flush everything else, and call it good. I figure at worst, it means that instead of ending up with perfectly fresh brake fluid, it is equivalent to ending up with how the fluid would be after a couple of weeks following a full-procedure flush.

If I screwed up the bleeding, replaced components, etc. and got air in the ABS, that would be a different story, where full-procedure flushing would be required.
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  #22  
Old 02-01-2020, 08:11 PM
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The simple steps are for a normal seasonal flush. See any dealer or Indy for the same quick version flush. No need to cycle the ABS system as there is no air bubbles or solenoids in their locked or blocked mode.
Now regarding the technical aspects of an ABS block in a Bosch version 3 or ver 4 system, there is a few manuals on their operations and test methods, all of which is way beyond the scope of a DIY Forum. The operation and fluid flows schematics are there for a deep dive.
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