Does all the brake fluid get out of the brake system?


Asked by cbbv Aug 03, 2014 at 08:09 AM about the 1990 Opel Corsa

Question type: Maintenance & Repair


If I open the wheel cylinder nipples and let the old brake fluid, flow out of the system(into a bottle) by gravity,
will ALL the brake fluid in the system flow out?
At the image of the dual master cylinder that I attached, it looks like that the brake fluid in the circle parts, which I marked as A and E, will not flow out.
Will the brake fluid in those parts(A and E)really stayed in the master cylinder or will they, also, flow out of the system?
I will very appreciate if you can answer directly to my question.
Thank in advance.

3 Answers


Hi tom. If you may look at my attached image,we can see that if we will open the wheel cylinder nipples and let the fluid get out by gravity: 1)the brake fluid from the resevoir will flow out. 2)the brake fluid around the first and second circuit return spring will flow out. 3)and the brake fluid in the copper pipes,also, will get out. But i try to figure out if the fluid in the circle area will stay in the master cylinder or get out by looks like the rear seal is disturbing the fluid to get out,or maybe,in fact,the fluid is getting out through the equalization ports,continue through the fluid intake and return ports to the copper line pipes and out? What do you think? It is not critical if air will get into the system.Anyway,when you add fresh brake fluid and let it flow out by gravity,it will push out all the air.At that situation we need to keep the new fluid in the reservoir between the lines. But the air is not the issue. I hope that you can answer my question This is very important issue for me. Thanks in advance.


Mechanics do not let the brake fluid just "flow out" by gravity- It won't work like that anyway- the brake lines do not reside vertically in your car- they are mostly horizontal- you need a container to pump the old fluid into then have someone start pumping the brake pedal while the old fluid pumps out- watch the reservoir and fill it up as it empties out- start with the longest line- this way you have replaced ALL the old fluid with new, and you have no air in the lines- this info is not for ABS- the rest of that stuff you are saying makes no sense to me- are you trying to re-invent the wheel?


I am not talking about how to bleed brake fluid.I know it very good and I did alot of times bleeding with an assistanse.i know all the theory a bout it and it is not the problem. The issue is that i am trying to figure out if the fluid in the master cylinder(the parts that i drawn a circles) will get out?(this is the main question). It is not make difference if the pipes are mostly horizontal,the low point is the wheel cylinder so the fluid will flow to the low point(from experience).what i am trying to figure out,again,is if the fluid in the master cylinder(with black circle)will remain in that parts all flow out.

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