BMW Questions? Ask a BMW Repair Expert for Answers.
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Did you remove the line that goes out to the wheel with no fluid flow?
The means the ABS Unit is bad. Its rare but when fluid wont flow through it freely a valve fell apart inside of it clogging the output to the wheel.
A good place to find a good used is in this link: http://www.bmrparts.com/index.htm
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It can only be the valves inside the abs unit. If it was electrical the the abs pump would run all the time. When the car is stopped the abs unt is open inside and it lets fluid flow right through it to the brakes.
Where did you get the booster and is it getting good vacuum?
Are you sure the abs unit you have now is right?
Is the fluid flow the same on both sides?
How bad is the pedal like dangerous to drive?
How did this problem occur?
Do you have a brake hose like this one?
I'm out of ideas. Ill have to opt out of this one. Maybe another expert can help.