reverse bleeding rear brake trapped air question - Kawasaki Versys Forum
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post #1 of 7 (permalink) Old 02-02-2020, 10:04 AM Thread Starter
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reverse bleeding rear brake trapped air question

Hi all,

I popped and clean the piston and check for any deposit (not a full caliper rebuild)
put it back in, suck all fluid almost dry by bleeder valve (I didn't want to push dirty fluid up in the abs nor having to empty the reservoir many times).

I knew such operation means the circuit would be pretty much dry and so I planned for it, with a big seringe to reverse bleed the brake, practically eliminating air infiltration.

It went well until everything was back in place when I started priming the pedal. 50 strokes and piston still not moving. Clearly some air trapped somewhere.

I turned ignition on, expecting the ABS unit to move something, hoping for some luck.
And it worked, but it still took 30+ strokes to feel hard (insert sexual pun)...

On top of that, waiting a 10-15 sec would remove the hardness, as if air would escape. And the later priming would take less and less strokes every at try.

QUESTION: what is going on in there? Air goes up , reverse bleeding should have been immune to such issue. At no point did I pushed any air bubble up in the circuit.

My hypothesis is that there are corners trapping air in the abs module. But Nothing in the manual says anything about special considerations for refilling after caliper maintenance... It just the standard fill from the top, which wouldn't make air eviction any easier.

(I'm not touching the front brake until I have a solid explanation or better method..!)

Last edited by fasteddiecopeman; 02-03-2020 at 02:03 PM.
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post #2 of 7 (permalink) Old 02-02-2020, 10:08 AM
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Interested to see how this turns out, I have not done brake fluid on an ABS bike before, but its gotta happen this winter.

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post #3 of 7 (permalink) Old 02-02-2020, 10:58 AM
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Bad Idea using pump

A recent post about vacuum brake bleeder. It is never a good idea to use a pump to get rid of air, as a example, the cooling system, on a drained cooling system, fill complete system and let sit before starting, first start watch rad level, stop immediately when fluid drops, refill and keep doing this untill no change, then allow to warm up and watch as soon as the T stat opens stop again, refill then put rad cap on and make sure overflow reservoir is filled, do a complete heat cool cycle then start again once cooled down, this is the final air purge. Yes we aren't talking engine cooling here. A vacuum brake bleeder removes air, all air, something near impossible to do using ordinary bleed screws.

Here is one of those threads about vacuum bleeder

mention also in this thread by Randy, speed bleeders

Last edited by onewizard; 02-02-2020 at 11:03 AM.
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post #4 of 7 (permalink) Old 02-02-2020, 12:57 PM Thread Starter
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Originally Posted by onewizard View Post
... It is never a good idea to use a pump to get rid of air,
.... A vacuum brake bleeder removes air, all air, something near impossible to do using ordinary bleed screws.
Here is one of those threads about vacuum bleeder
I used a syringe with a long clear hose to see through and ensure any bubbles (and there were none) do not reach the nipple while pushing fluid in in 1 single stroke over a few minute (blocking the piston, btw!) until the fluid shows up in the top reservoir.

Vacuum bleeding means the only exit is down, fighting air bubbles that want to go up.
Not to mention how off-throwing it is to see endless bubbles coming from the bleeder valve simply not being air tight.

That's the whole advantage of pressuring fluid from below and upward. If the bleeder valve isn't sealed, sure it may leak fluid under pressure but no air gets in.

I cannot conceive of the physics it would take to claim vacuum is better unless one could vacuum from the top reservoir, and even them air would sneak in from the bleeder. There is a reason the manual wants you to pressure the pedal to exit the fluid.

I'd rather say vacuum is never a good idea...
But that is beside my question.

I only want to know if there are special moves to make in relation to ABS, like run it, get it to activate, tilt it, or anything suspiciously missing from manual that long bearded mechanics know about...

Last edited by dddd; 02-02-2020 at 01:29 PM.
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post #5 of 7 (permalink) Old 02-02-2020, 06:15 PM
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Apologies I don't have a long beard but since I just bled my 2015 V1000 after rebuild the caliper I thought I can share my experience and research-
The service manual just says to bleed the brakes even when replacing ABS components. Based on that there is only one suggested way to bleed brakes regardless of activity.
Not being a wise guy but (its in my genes) You para phrase the manual saying there is a reason it wants you to push the pedal however your technique was different.

If we put aside the right way to do this and assume Kawasaki's method works, I would suggest you check your work at the caliper for any obvious leaking and try a bleed using the factory recommended procedure and see if you see any air coming out. You pushed it in now pull it out :-) I did not run my system dry so I may be way off.
The other thing this does is test the master cylinder to see if it pushes fluid out the bleed nipple, maybe that will give some clues.
Either way best of luck to you and I hope you get a speedy resolution
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post #6 of 7 (permalink) Old 02-03-2020, 02:32 AM
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FWIW I tried the "syringe to the bleed valve" method and I couldn't get any fluid through. I figured the ABS model has longer lines that require more pressure that I can generate with a syringe to feed the fluid through. Didn't know about the zip-tie trick though, maybe that would have helped. Also, the ABS lines that go along the frame into the ABS pump are routed pretty much vertically through some of their length, so you can still get bubbles there, regardless of which method you use.

I've managed to bleed my ABS model from a dry state (replacing lines) and it took *a while*. Several days. It included having to suspend the calipers above the master cylinder to get some of the more stubborn bubbles out. I used a combination of the classic pumping the lever method with a vacuum pump on the other side.

The rear brake was easy peasy, just a short while of working the pedal. I don't remember if I used the vacuum pump, but it went smoothly.

I didn't use any fancy technique to handle the ABS pump, just normal bleeding, only somewhat harder due to the length and routing of the lines. Since then, I've managed to trigger the ABS while riding many times and it works fine.
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post #7 of 7 (permalink) Old 02-04-2020, 05:47 PM
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Using a syringe & plastic tube, I reverse bled the front ABS brakes on a 2009 1250 Bandit several years ago. It worked like a charm with no ill effects. Unless the ABS design is way different on the Versys, I can't think of why it wouldn't work.

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