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Old 11-02-2011, 09:19 AM
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bluebee bluebee is offline
Seek to understand,^Value
Location: San Jose, California
Join Date: Mar 2008
Posts: 25,236
Mein Auto: 02 BMW 525i M54 auto 130K
Originally Posted by Fudman View Post
RDL's .pdf file gives a good explanation.
I had trouble understanding their explanation (but not yours). It troubled me that their hoses and tubing (E85) were in different places than ours are (E39).

Originally Posted by Fudman View Post
The sucking jet pump is not a "pump" at all
Now that's interesting!

Originally Posted by Fudman View Post
just a fitting that creates a vacuum for the master cylinder to boost braking power.
That description makes it sound more like a 'valve' than a 'fitting'?

Originally Posted by Fudman View Post
manifold vacuum draws air from the intake bellows through the fitting (jet pump). The fitting constricts the air flow, increasing airflow speed which creates a venturi effect, which then causes a pressure drop. The angled fitting connection (which is attached to the brake master cylinder) is exposed to this pressure drop which creates a vacuum in the line. This vacuum is used to boost the brake master cylinder.
Wow. I just realized, reading your explanation, that the big fat drum that is in 'most' cars for power brakes, doesn't exist in the E39!

Does the SJP take the place of that thing?
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