Article [13] ST1300 - Brake Maintenance - Getting all the air out of the brake system

Peto said:
The best way of getting air bubbles removed from a tube or brake line is to make sure there are no high/low points in between.
Make sure one end is higher so the bubble will rise.
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Actually, the best way is to tilt the tube so that the fluid going down and the bubble going up do not block each other's progress.
But most of the brake lines are fixed in place at certain points. It isn't possible to ensure one is higher then the other. And there are two large 'n' shaped bends in the hoses both under the headlights. You have got to flex, tap, and manipulate the tubes to encourage bubbles to move along with the flow.

But your point is well taken. The clutch and the front lever / front caliper circuits are quite easy to bleed.
 
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Sadlsor said:
Errr... I guess boiling DOT 4 in a pan on the stove before infusing the brakes is out of the question then?
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Boiling on a stove probably won't do it a huge amount of good...

...but 'boiling' it by applying vacuum... Certainly helps get air out of fluid that's been 'well shaken' in the container. Longer term application of vacuum should help remove water as well, but that's possibly a little excessive (and wouldn't, for example, undo oxidation or other chemical changes in the fluid due to moisture).

But as the brake fluid doesn't tend to go much below ambient pressure during use, it's surprising how little difference removing the entrained gas make! (A small research project while at uni...)
 
Sadlsor said:
Errr... I guess boiling DOT 4 in a pan on the stove before infusing the brakes is out of the question then?
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That's not the point I was making.
The point was trying to use logic for instance if you want to bleed the rear of the ST1100 and don't have any fancy equipment.
You could lower the calliper since the line is partially flexible, but you have to remove the tank and the wheel of course.
 
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I was making no point.
Just being my usual sarcastic self, and sarcasm is my best and only offering here, in many cases.
I am an annoyance to some, indulged by others, and ignored by the rest.
No offense intended, but you get to choose which.
 
Peto said:
The best way of getting air bubbles removed from a tube or brake line is to make sure there are no high/low points in between.

This process can be speed up if the temperature is higher hence viscosity will be lower.
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As said, the brake lines are fastened in place. However, a good bike rotisserie will make tilting, inverting, and otherwise chasing bubbles easier. @Mellow just bought one of these things, I think it's called a Sky Lift. While you are fussing with all the tilting, I'll stick with my vacuum bleeder setup.:biggrin:
 
mjc506 said:
...but 'boiling' it by applying vacuum... Certainly helps get air out of fluid that's been 'well shaken' in the container. Longer term application of vacuum should help remove water as well, but that's possibly a little excessive (and wouldn't, for example, undo oxidation or other chemical changes in the fluid due to moisture).
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On the assembly line, brake systems are filled automatically using the "evacuate and fill" method (which is the method used for industrial hydraulic systems in general, not just brake lines).

The brake fluid itself is often conditioned by being "boiled" under vacuum before filling.

Evacuation and Fill — Dominion Technologies Group, Inc.

www.dominiontec.com www.dominiontec.com
.

www.siqinc.com

Vehicle Manufacturing | ACCUFILL Brake Fill Equipment

The AccuFill A/C Fill System offers our premium a/c charging technology without the DatServ.NET Data Acquisition and Process Control option.
www.siqinc.com www.siqinc.com
.
 
mjc506 said:
But as the brake fluid doesn't tend to go much below ambient pressure during use, it's surprising how little difference removing the entrained gas make! (A small research project while at uni...)
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However....from sea level here in Houston you can be on your ST at 14000 ft the next day in Colorado (where the atmospheric pressure is getting close to half the sea level pressure) ...and it is not unusual for the brakes to feel mushier up there, specially going down passes with a fully loaded bike.

And will feel solidly firm again once back at sea level.

Not just the ST though, you can experience the same in a car.
 
Peto said:
The point was trying to use logic
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Contrary to belief, that doesn't always work .. or may not be the most efficient (or safe?).

SMSW said:
'll stick with my vacuum bleeder setup.
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Thanks - same here, with all vehicles, bike or one with 4 wheels. I also use a pressure feeder, so I'm not constantly having to add more DOT every few minutes.
 
Sadlsor said:
I was making no point.
Just being my usual sarcastic self, and sarcasm is my best and only offering here, in many cases.
I am an annoyance to some, indulged by others, and ignored by the rest.
No offense intended, but you get to choose which.
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Sorry I didn't want to be mean. I wanted to explain my idea. so apologies
 
No need to apologise for making a perfectly valid comment @Peto . You'll get used to @Sadlsor .... he never makes a comment that is aimed at a person. His quips are usually a sideways look at a thought triggered by something he has read. Great fun to read, rarely provoke a laugh, but usually manage to raise a smile.

I don't know if there is a 'like' emoji for that ! There ought to be. A half smile ?.;)

I had never thought about bleeding in Summer Vs Bleeding in Winter. I always do my servicing in winter because then if I cock it up, I have plenty of time to put it right before the Summer rides begin. I used to ride all year round, but now I don't have to !
 
jfheath said:
.... get used to @Sadlsor .... he never makes a comment that is aimed at a person.
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Except at Sadlsor himself!


jfheath said:
His quips are usually a sideways look at a thought triggered by something he has read. Great fun to read, rarely provoke a laugh, but usually manage to raise a smile.
Click to expand...


Nonetheless, a thread is not a thread if it hasn't been Sadlsored!


.......
 
jfheath said:
No need to apologise for making a perfectly valid comment @Peto . You'll get used to @Sadlsor .... he never makes a comment that is aimed at a person. His quips are usually a sideways look at a thought triggered by something he has read. Great fun to read, rarely provoke a laugh, but usually manage to raise a smile.

I don't know if there is a 'like' emoji for that ! There ought to be. A half smile ?.;)

I had never thought about bleeding in Summer Vs Bleeding in Winter. I always do my servicing in winter because then if I cock it up, I have plenty of time to put it right before the Summer rides begin. I used to ride all year round, but now I don't have to !
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:thumb:
 
I'd l ike to thank John for his awesome PDF. Just finished bleeding after changing the SMC, man what a pain! The flow diagrams for each piston(s) were key in helping me understand why/where the bleeding is complicated.
 
I have to read all the other messages from the one with the PDF and ahead yet, but I cannot let it go my burden to say that's pretty sad you say in the PDF file that it's not a scientific demonstration the thing with the water and tubes and that. O yes it is, and this behaviour is what took science ahead, doing these experiments and tests. It's exactly PRECISELY that. It's not an advanced demonstration, but it's the one needed to be 90% sure fluids will behave like that in our brake lines.

Science goes far beyond academic degrees and peer pressure from other priests of scholar entities.

I'm doing my ST1300 right now and it will take kinda 4 more months to finish it, because money and time. I completely dissasembled the brake systems and I'm cooking a plan to fill it back with clean fluid that might be interesting. I'll use 3D printed parts (maybe), an AC vacuum tool, and a device I'm creating to put brake fluid with high pressure inside the lines. I'm sure it will be interesting. I'll put the thing in the thread about it that you can find in my profile. Also I'll do it as easy as I can in order to people to be able to copy it without spendint too much work, money or time. I love doing these things complicated, but if I can get a way for others to benefit from it I would rather get that.
 
MidLife said:
Why reinvent the wheel. Commercial/industrial oil filling devices are vacuum driven.
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Vacuum driven works different and in reverse flow than the best for taking bubbles out. This is more than a wheel in this case, and is not as "user friendly" as commercial common tools. Just wait to see it and you'll understand why is not an easy to sell device. Maybe in the future they will make a commercial device with this method. Nothing new under the sun, but the style always evolves.
 
Thank you for your kind comment @leodante. I started looking up stuff about fluid dynamics when I carried out my experiments and the more I skimmed (because that's all I could take in) the more I realised that I knew nothing about it. But also realised that blowing fluid through a straw must give a pretty god idea of what was going on.

I didn't want to come across as someone who knew what he was talking about. But the ink in coloured water paints a pretty good impressionist view, I think.

There is a one way valve in the rear brake line circuit - located in the inlet port of the SMC. I believe that it is there to help with normal brake bleeding. (Ie pumping the pedal, lever). I don't know but it may cause problems when trying to push fluid through from the bottom. Fluid will still get through the tiny compensation port, but it may take a while.

Vacuum pumps are good for filling the system from empty. But useless for chasing bubbles and you will get those whether you use a vacuum pump or a pressure based system. Air will still get trapped on the side walls and at joints. My first demonstration video was pressure based - I was blowing air into a bottle of coloured water and that pushed the fluid through. You saw how bubbles still got trapped.

The traditional bleed tube works well - especially if it has a non return valve on it. But for best effect you use the lever to pump up the pressure with the bleed valve closed and then hold the pedal/lever to seal off the inlet port and compensation port and open the valve and let the built up pressure push the fluid and air through. Close the valve before the pressure gets to zero (watch the movement in the bleed tube).

Repeat. You also need to tap joints, flex lines to get all of the air out.
 
MidLife said:
Nice vid, but dIfferent fluid, different viscosity, different surface tension, different hose material, different hose diameter, most likely not really representative of entrainment in actual brake line.
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I never pretended it to be an accurate representation of what happens inside the brake lines. And it is for that very reason that the opening paragraphs in the pdf document make those very points. Quote:

Part way through writing this article, I started to question my own understanding of how bubbles behave in a tube of flowing liquid. It was time to take a look at what actually happens, so I started with some research papers which made me realise how big a topic this is, and how long ago it was since I did my maths degree. ​
There are far too many variables to put together a definitive method for getting rid of air, but a little understanding does not go amiss. What follows is not conclusive by any stretch of the imagination. A proper study would consider the flow rate, the internal diameter and nature of the tube, the size of the bubble, the viscosity and surface tension of the fluid, the shape of the tube and its relationship with the vertical and the horizontal, and a load of other stuff.​
No - this page is not a proper study, but it is interesting. I have a large bottle of coloured water. When I blow into one tube, it forces the coloured water down the tube that you can see in the photo. There are no bubbles in the liquid itself, but bubbles can be seen trapped against the inside of the tube, and bubbles and pockets of air form as the fluid flows. ​
The picture is a link to a YouTube video. It is not a scientific demonstration. It is not brake line and it’s not brake fluid. But it is flowing fluid, there is air in there and we can see where it is going. Or not, as the case may be.​

So it was only ever for interest purposes only. Playing with tubes of coloured water showed me things that I didn't expect to happen. I found it revealing that bubbles automatically gather where there is an irregularity in the internal surface of the tube; that the fluid flowed straight past an almost vertical column of air; that air can be trapped in U bend while the fluid flows underneath it. Which suggests that no matter how log you suck fluid throught - unless something changes (shape, flow, angle.....), those bubbles are not going to shift. Some observations from that video may well apply to brake fluid in the narrow channels of the brake lines. I haven't got a clue which they would be, if any.

As for vaccuum pumps. I have one -it is a Sealey hand operated pump and it is OK for what I want. it gets the system filled quickly and it provides a flow of fluid so that I can go round tapping the joints and flexing the tubes. But it is cheap, nasty, it leaks, it makes a mess and I hate using it. But I cannot get my brakes as firm as I want them without using the standard non-return bleed tube to finish off. And it only ever comes out if the lines have been emptied. Most of the time I use the half unused bottle from my last fluid replacement to flush out any grunge, sluice the pistons and then use brand new sealed to flush all of that out and bleed.

Maybe with professional equipment. I wouldn't know, I have never tried.
 
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