Bleeding Your Master Cylinder

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RZResurection
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Bleeding Your Master Cylinder

#1 Post by RZResurection » Sat Sep 07, 2013 9:05 am

Here is an awesome tip suggested to me by forum member JonW.

An easy way to help bleed out air that may be trapped in your master cylinder is to wrap a cable tie around your brake lever and let sit for at least a day. Make sure that you fill the reservoir first. The level will drop as the trapped air is released.

Simple!

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JonW
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Re: Bleeding Your Master Cylinder

#2 Post by JonW » Sat Sep 07, 2013 9:31 am

Do this with the lever in the largest span position, not the closest, and get it as close to the bars as possible.

You can do this a few times and you usually improve the lever each time.
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RuZty
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Re: Bleeding Your Master Cylinder

#3 Post by RuZty » Sat Sep 07, 2013 10:13 am

I do it the old fashioned way but rotate or remove the clip on to a position that the air can get out of the MC.

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rztom
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Re: Bleeding Your Master Cylinder

#4 Post by rztom » Sun Sep 08, 2013 11:02 pm

Great tip - been doing this for years and IT WORKS :smt023

Agree with Jon... I put the zip tie mid-point on the lever/grip and cinch 'er down tight. I find that after a couple of hours it's all good - no need to wait a day... :smt004

Bare
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Re: Bleeding Your Master Cylinder

#5 Post by Bare » Wed Sep 25, 2013 7:51 pm

Yeah.. it works .But then so does reverse bleeding using a cheap Plastic Disposable Syringe.. And you need not wait overnight.

Moxon
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Re: Bleeding Your Master Cylinder

#6 Post by Moxon » Sat Mar 19, 2016 9:59 pm

I'd be curious how this works. The seals in the MC would prevent air from getting out from the top.... is it helping migrate the air towards the bleed valve of the caliper?

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JonW
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Re: Bleeding Your Master Cylinder

#7 Post by JonW » Sat Mar 19, 2016 11:27 pm

no air comes up...
80 XT500 Supermoto!
81 RD350LC Resto
82 RD421LC Hybrid
82 RD350LC decapitation project
82 RD250LC JDM '251LC' YPVS
83 RZ350 Resto
84 RZ500 Resto
85 RZ350 F1 Resto
86 RZ350 F2 Resto
86 RZ350 F2 Hybrid

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MK
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Re: Bleeding Your Master Cylinder

#8 Post by MK » Sun Mar 20, 2016 1:24 pm

How it works is explained easily: if you hold a high pressure for a longer period of time the air is dissolved in the brake fluid. When you release the pressure, the air will build up small bubbles, but not necessarily at the same location than before. If it is in the master cylinder or the reservoir, that air does not hurt as the bubbles can "escape" easily.

It's the same that happens to your soda when opening the cap. It contained gas under high pressure and releasing the pressure drastically lowers the quantity of gas that can be dissolved.
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JanBros
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Re: Bleeding Your Master Cylinder

#9 Post by JanBros » Mon Mar 21, 2016 8:04 pm

I think your explanation is flawed in many ways :

why would you need to leave it under pressure overnight ? It's not that the pressure keeps on rising. Just holding it for a couple of seconds should have the same result, yet it doesn't ...

and on the releasing bubbles in soda : if you open the cap, you'll see that the bubbles are formed everywhere in the soda, not just "on the top", so the result would be the same as before the pressure : very small bubbles everywhere.
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whyzee79
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Re: Bleeding Your Master Cylinder

#10 Post by whyzee79 » Mon Mar 21, 2016 9:03 pm

Has to do with the fact the air is compressable but the fluid isn't. It gets squeezed together and migrates to the top master but it takes time. That is why the brake is spongey in the first place. That's what I'm thinking. I think its Boyles law or something like it.

tacky1
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Re: Bleeding Your Master Cylinder

#11 Post by tacky1 » Mon Mar 21, 2016 9:47 pm

Another tip to get the lever rock hard, Flick the end of the lever really lightly so it bangs against the piston, It can take a while, But you will see tiny bubbles rising in the reservoir.
Even after bleeding, you will see the micro bubbles, Lever will be solid after doing this, Then leave it for a night or two with the zip tie,
This is how I bleed my brakes for years, Never failed.
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justind97
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Re: Bleeding Your Master Cylinder

#12 Post by justind97 » Tue Mar 22, 2016 8:17 am

I had a hell of a time with a Brembo square style reservoir that's integrated into the housing, like a stock RZ. It was completely spongy and wouldn't get hard despite me using a vacuum bleeder.

One thing I discovered was the micro bubbles were coming up, but I couldn't get them to the surface to pop and remove from the system. Eventually I figured out that by squeezing the lever and sitting there flicking the reservoir helped get the bubbles out. I spent a good 10 minutes tapping and flicking and eventually I saw a fair amount of bubbles coming out of the system. After that the lever was rock hard and had great feel.
The zip tie method works, but if you're impatient tap the reservoir.

RZ masters are simple to bleed, all of 2 minutes total with a vacuum bleeder and you should be good to go.

RuZty
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Re: Bleeding Your Master Cylinder

#13 Post by RuZty » Wed Mar 23, 2016 7:30 pm

I found with a stock style integral reservoir setup that if I loosened the clip-on handle bar and rotated it so the cylinder bore was uphill to the reservoir it helped get the air out.

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JonW
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Re: Bleeding Your Master Cylinder

#14 Post by JonW » Wed Mar 23, 2016 7:54 pm

All great tips here, keep em coming... The more of the things you try from what you read here the quicker those bubbles will come out.
80 XT500 Supermoto!
81 RD350LC Resto
82 RD421LC Hybrid
82 RD350LC decapitation project
82 RD250LC JDM '251LC' YPVS
83 RZ350 Resto
84 RZ500 Resto
85 RZ350 F1 Resto
86 RZ350 F2 Resto
86 RZ350 F2 Hybrid

Like Watches? www.PloProf.com & www.DeskDivers.com

Moxon
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Re: Bleeding Your Master Cylinder

#15 Post by Moxon » Thu Mar 24, 2016 1:19 pm

I was thinking of getting a vacuum type brake bleeding system, like a Mighty Vac. Anyone used these with any success?

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