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Old 09-24-2013, 05:58 AM   #1
rtbain OP
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Wicked Brake fluid exits vent during reverse bleed, WTF?

I have read the FAQ but cannot find a reference to this. Replaced the lines on a friends 1150 w/abs. My drill is to fill from the bleeder. After a bit brake fluid began draining from the vent tube near the right peg. Did the same front and rear.

Went on with the bleeding process and got nice firm brakes. (Wish I would have read the articles here fist but that is another story). Will bleed the ABS unit next.

My question is how does a reverse fill cause brake fluid to come out the drain lines? For that matter why is the brake system open to atmosphere?
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Old 09-24-2013, 07:13 AM   #2
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Quote:
Originally Posted by rtbain View Post
I have read the FAQ but cannot find a reference to this. Replaced the lines on a friends 1150 w/abs. My drill is to fill from the bleeder. After a bit brake fluid began draining from the vent tube near the right peg. Did the same front and rear.

Went on with the bleeding process and got nice firm brakes. (Wish I would have read the articles here fist but that is another story). Will bleed the ABS unit next.

My question is how does a reverse fill cause brake fluid to come out the drain lines? For that matter why is the brake system open to atmosphere?
There is no vent tube for the brake system. It is sealed. The tube near the right peg is the water drain from the gas tank filler. Water that gets past the cap drains down that tube. If someone has removed the evaporative canistor, then it could also be a fuel overfill. But it better not be brake fluid, or something really strange is going on.

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Old 09-24-2013, 07:35 AM   #3
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Maybe the brake fluid reservoir is overflowing and that tube just runs next to it so the fluid appears to be coming from the tube.
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Old 09-24-2013, 07:44 AM   #4
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I have no idea what you are talking about....brake fluid coming out a vent line???

Just a general comment; before messing with brake systems, one had better fully understand the system mechanically, electrically and hydraulically. Brake systems are more complex than ever. Its not just a couple of pistons and some DOT4 anymore.

We have turned into a passive, lazy society...we want the answers before we take the test...it doesn't work that way.

Do your homework before you begin. Diagnose your problem and report back...your life may depend on it.
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Old 09-24-2013, 08:18 AM   #5
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ABS module reservoir vents

If you look at the filling caps of your ABS module you will find they are both vented. Two overfill lines into a Y and drained to the ground.

As you may be aware now, the braking system have 2 controls circuits: from the the handlebar lever to the ABS pump, and from the right foot lever to the ABS pump. And 2 "working" circuits: from the ABS module to the front calipers, and to the rear one.

If you push fluid from the calipers up, either by "pumping" it or by spreading the brake pads all the way, without opening the reservoir caps... the fluid have to go somewhere , right? That's when you will see drainage.

This may help:

http://advwisdom.hogranch.com/Wisdom/service_abs3.pdf

http://bmwsporttouring.com/ubbthread...t&Number=10156
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Sporttour screwed with this post 09-24-2013 at 08:24 AM Reason: added wisdom ;)
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Old 09-24-2013, 08:20 AM   #6
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I'm not a certified BMW Tech..but I did stay at a Holiday Inn Express last week..

You got brake fluid coming "out" of anywhere..you got a problem..



My$.02, I know lotsa folks have done it (in autos) but I have never had good luck reverse bleeding anything..

If you close the bleeders and squeeze the lever or pedal, does it leak out somewhere?
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Old 09-24-2013, 08:25 AM   #7
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If you push fluid from the calipers up, either by "pumping" it or by spreading the brake pads all the way, without opening the reservoir caps... the fluid have to go some were, right? How did more fluid get in there from when it started? That's when you will see drainage.
See what I'm saying? you started with x fluid...used brakes..they wore.letting fluid level drop in reservoir...then you push pistons back, you have the same amount of fluid as when you started?? Unless someone added fluid..which..you shouldn't..

No..wait..your saying he swapped his stuff..and started pumping fluid up from the bottom with out removing caps?? OK..I get that..yeah..they only hold so much..
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Old 09-24-2013, 08:32 AM   #8
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and the winner is....

Thanks for the links and the education. I feel much better now. AND the vent lines have been bleed as well.

Quote:
Originally Posted by Sporttour View Post
If you look at the filling caps of your ABS module you will find they are both vented. Two overfill lines into a Y and drained to the ground.

As you may be aware now, the braking system have 2 controls circuits: from the the handlebar lever to the ABS pump, and from the right foot lever to the ABS pump. And 2 "working" circuits: from the ABS module to the front calipers, and to the rear one.

If you push fluid from the calipers up, either by "pumping" it or by spreading the brake pads all the way, without opening the reservoir caps... the fluid have to go somewhere , right? That's when you will see drainage.

This may help:

http://advwisdom.hogranch.com/Wisdom/service_abs3.pdf

http://bmwsporttouring.com/ubbthread...t&Number=10156
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Old 09-24-2013, 08:38 AM   #9
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Old 09-24-2013, 08:53 AM   #10
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Originally Posted by rtbain View Post
I have read the FAQ but cannot find a reference to this. Replaced the lines on a friends 1150 w/abs. My drill is to fill from the bleeder. After a bit brake fluid began draining from the vent tube near the right peg. Did the same front and rear.

Went on with the bleeding process and got nice firm brakes. (Wish I would have read the articles here fist but that is another story). Will bleed the ABS unit next.

My question is how does a reverse fill cause brake fluid to come out the drain lines? For that matter why is the brake system open to atmosphere?
And you ask where the "extra" fluid came from?

When servicing the ABS, the procedure is to fill the reservoirs to the line with the pads seated all the way to the discs... If you push the pistons back to the calipers, the fluid does not have enough room in the reservoirs and WILL come out of the vents. If that happens and the reservoirs are not refilled, they will run low on DOT 4 when the pistons return to their working position.
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Old 09-24-2013, 08:58 AM   #11
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AND the vent lines have been bleed as well.
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