Constant air while bleeding rear brake control line - BMW Luxury Touring Community
 
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post #1 of 7 Old Mar 8th, 2012, 10:22 pm Thread Starter
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Constant air while bleeding rear brake control line

OK, what is going on here? I have replaced all the brake lines on my '05 with Speiglers and I am bleeding the rear control circuit. I have gone thru an entire 12oz bottle of DOT4 and still I'm getting a constant tiny stream of air in the bleed line. I've tried reverse filling and I've been using the old school method for bleeding to prevent any of the air that does bleed out from going back in. Any chance this air is coming from the bleeder valve?

'15 GTLE


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post #2 of 7 Old Mar 9th, 2012, 5:31 am
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Re: Constant air while bleeding rear brake control line

Check the supply line between the res and master cylinder for twists and kinks.
Bleeding old school shouldn't induce air in the bleed hose (depends on how tight your bleed line fits the nipple) it is common with vacuum bleeding.
Tighten the bleed nipple when the brake pedal reaches half it's stroke, don't use the full travel.
Follow the bleed procedure 1-2-3-1
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post #3 of 7 Old Mar 9th, 2012, 4:49 pm
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Re: Constant air while bleeding rear brake control line

Also try smearing a little grease at the base of the nipple (on the threaded end) to prevent any "induced" air. Once you have a firm pedal you should be OK as a bit of tiny air bubbles in the control circuit is not a big issue. Then check again in week or so to see if those tiny bubbles have coalesced into a bigger one. I usually get a stream there even during a flush if I open the bleeder too much.

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post #4 of 7 Old Mar 9th, 2012, 5:01 pm Thread Starter
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Re: Constant air while bleeding rear brake control line

This is exactly what I was thinking too. The base of that nipple is very loose when opened up even slightly. I'm off to get some more DOT4 and since this cicuit is very clean right now, I'll run the bleeder back into the reservior and run it through some more with some grease on it. Thanks for that suggestion, I'll report the results soon.

'15 GTLE


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post #5 of 7 Old Mar 10th, 2012, 7:07 am
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Re: Constant air while bleeding rear brake control line

On a reverse fill it can pull air in due to the pressure differential but I think when using the old school method you will have positive pressure at the bled nipple and would see leaking at the bleed nipple threads not air being pulled in.Maybe it's cavitation at the end of the nipple, high pressure low flow to low pressure high flow when the bleeder is opened and not actually air in the lines.
Just a thought and hope it works out.
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post #6 of 7 Old Mar 10th, 2012, 11:02 am Thread Starter
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Re: Constant air while bleeding rear brake control line

I finally got it to bleed without air by just barely opening the bleed nipple and basically forcing a slow, high-pressure stream. Got about 18" of air-free fluid in the bleed hose, so I feel confident all is good. All brake lines are now bled, the slave cylider and seals are replaced and the clutch is bled. Ready to put the swing arm back on!!! Gonna be in the 60's all week, so with a little bit of luck I'll be riding. Thanks everyone and can't wait to see those of you going to CCR!!!

'15 GTLE


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post #7 of 7 Old Mar 10th, 2012, 12:12 pm
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Re: Constant air while bleeding rear brake control line

Great job, Steve! The 36k service on mine is about 300 miles overdue...but the honeydo list has to come first.

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