Cloudy brake fluid reservoir

jlparsons · Derestricted Danger Joined: 02 Mar 2019 Karma :

Hi folks, have noticed my brake fluid reservoir has a cloudy bit at the bottom which separates and sinks when the bike hasn't been moved a while. It then remixes when the brake is applied. Is this normal or does the fluid need replacing?
F800gt 12000 miles.

Riejufixing · World Chat Champion Joined: 24 Jun 2018 Karma :

I'd be inclined to change it, it could be water, or water in old/ incompatible fluid, or something else you don't want in there.

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

I'd change it. You may find you can suck out most of what's in the reservoir (just don't uncover the hole) then put fresh fluid in from a new bottle and start running it through (it'll usually go with gravity if you crack the bleed nipple).

If you attach a clear hose to the bleed nipple, you can usually see when the new stuff starts coming through, it's generally a slightly less yellow colour.

If there are lumps in the bottom of the reservoir, you may need to either flush it with a few changes of fluid or empty it totally and wipe it out. It may or may not need bleeding after that.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

Polarbear · Super Spammer Joined: 24 Feb 2007 Karma :

Is that not a sign of moisture in the fluid?

Whatever it is, time for a change as it's not exactly a huge financial hit to do even if you use a whole bottle flushing through the system.
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Triumph Trophy Launch Edition

MCN · Super Spammer Joined: 22 Jul 2015 Karma :

BMW put a little disc of open cell sponge in reservoir to prevent fluid aeration. I think it's due to bar vibration that agitates the fluid.
It's maybe the sponge you can see.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

jaffa90 · World Chat Champion Joined: 06 Apr 2016 Karma :

Over the years i`ve seen clear brake fluid and partly cloudy fluid but never seen floaters, all though not dangerous as yet i would be finding out what`s breaking up.

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

MCN · Super Spammer Joined: 22 Jul 2015 Karma :

https://www.ukgser.com/forums/showthread.php/473560-Brake-reservoir-sponge/page2

If it has a sponge and it wasn't replaced after a while it can disintegrate.
That would be 'solids'. There's nothing much in brake fluid to solidify. Glycol-Ether.
Unless contaminated by something not glyco-ether.
Water, oil, grease, etc.
Should be replaced every two years as it will absorb atmospheric moisture which reduces it's boiling point and can encourage corrosion and freezing at very low temps.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

What do you reckon this stuff is then?

It's in an old master cylinder reservoir out of my parts box. You can see brownish crystals above the "high tide" mark and a layer of varnisy sludge coating the inside of the reservoir. The fluid is a yellowy-brown. It was DOT4.

I'd suggest that while it was originally glyco-ether, a significant proportion of it is now something else. Probably hydrolysed to something else? (who'd have thunk it, exposing chemicals to extreme heat and pressure).

https://www.bikechatforums.com/download.php?id=103357
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

MCN · Super Spammer Joined: 22 Jul 2015 Karma :

Could be bacteria growing in water feeding on the brake fluid.

https://www.researchgate.net/publication/303745627_Microbial_growth_in_brake_fluids

Glycol can discourage bacterial growth if the solution is high enough.
Bacterial growth in cooling heating systems is controlled by bacterial inhibitors glycol is one.

The crystals could be a component of the alloy the master cyl is made from. Leached out by something. Oxidation by bacterial by-product or something more sinister. (Couldn't be sinister as the brake would normally be on the right side.)

I hope you drained it, filtered it through an old set of Y-Fronts and poured it back in?
👍
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.