Hydraulic Brake Fluids (A Relaxed Talk)

Stefan, I have zero experience in cold temperatures, but my recollection is the issue with mineral based hydraulic systems in cold is related to their BENEFIT - mineral brake fluid is hydrophobic , so water in the system separates out and then collects around the calipers
That might explain why this past spring when I did a fork and rotor swap, my brakes stopped working right after flipping the bike over for an hour, and why when I flushed the rear line there was bacterial growth in the system with me thinking "how did enough water get in there for this to happen?"

Though I also wonder how cheap the brake fluid Zoom uses in the brakes aventon sent me. The front which had no growth came out nearly clear when I did an actual flush of both.

And I mean a real flush; hot water forced through the line, then isopropyl, used a new caliper on the rear since Aventon sent me a spare (it came not working) and actually boiled the handle before again hitting it with IPA to help drive out moisture.

Though I'm wondering if the replacement I got off Amazon before Aventon even bothered responding to my help request was the one that was contaminated, or if I accidentally did so when I did the replacement initially.

Bacterial growth in fluid lines is a constant woe for me as a computer tech. This whole "liquid cooling" trend being a magnet for mold even with the additives people use. Especially homebrew and/or custom tubing, though we've seen a number of AIO's die for the same reason which is worse. With custom loops you usually use clear tubing so you can see the dye added to the water, so you can see when the colour goes funky. AIO's use rubber tubing so you can't actually see what's going on.

I wonder how mineral oil would behave compared to the water. I mean, we used to submerge whole computers in the stuff.
bateririal growth in brake fluid? Never heard of such a thing. it can darken but thats from that and such. I can't imagine putting water and alcohol in my brake lines.
bateririal growth in brake fluid? Never heard of such a thing.
Surprised the hell out of me 'cause I hadn't either. I mean mineral oil doesn't generally promote growth. I was thinking "how was there enough water in there for something to grow?" Was definitely bacterial too because I know that smell -- more like "stench of death" -- from working with PC's liquid cooling.

But if as @PDoz said extremes of cold can drive the water out, there's my culprit. I live in Keene NH, the bike was stored in an unheated garage, and in winter we get temps in the double digits negative Fahrenheit. February quite often -9F would be a warm night. (that's -23C for people not from countries that have been to the moon and don't think it's dumbass to have polar opposites be 100 degrees apart instead of 180.)

Doesn't explain the excess water that was in the front tube that I initially blamed on Flatout, but now suspect was in there from the factory. Froze solid so during winter rides it was actually throwing the wheel off balance making even flat road go "Elmer Fudd". Should have realized that wasn't Flatout's fault sooner when it was only the front tire exhibiting the behavior. Total hurr-durrz on my part.

As to the water and alcohol, near-boiling water is one of the fastest ways to kill off bacteria since most biologicals can't handle temps higher than the mid 170's (again Fahrenheit). So I pushed boiling hot water through the tubing (using a icing bag and tip of all things), blasted the water out with my air compressor, then ran a flush of alcohol which helps get rid of any residual water, to then hit it with the compressor and let it sit 24 hours before refilling.

Clean new caliper saved me time though I did end up disassembling and cleaning the one that was fouled, but I did have to clean the handle so that got taken apart, boiled in a pot, wiped dry, alcohol wiped, and put back together.

I swear I've learned more about how hydraulic brakes work internally and how to take them on/off a bike than I've ever wanted to this past year.

Sad I missed this thread earlier, the talk of the different fluids and alternatives is interesting, helpful, and useful. Having seen the inside of both caliper and handle on the Zoom ones, I can't see the engineering tolerances being tight enough to care about the difference between types of mineral oils and their additives. If the additives do anything I would think they'd not be so much about how it works for braking, but how it survives things like temperature, biological contamination, polymer breakdown, and so forth. The boiling issue under extreme braking for example I'd expect both mineral oils and glycol based to have additives specifically to mitigate that.

The pink Shimano stuff though, I swear it has Marvel mystery oil in it. Open up a fresh bottle and that's all I smell. I know it well, my old man used it as a household lubricant. Even used it as gun oil. Was like going back in time 40 years.

It actually seems weird Marvel now sells it as JUST a fuel additive. They used to advertise it as both that and as a general purpose lube. I even used to use it to lube the old 24" 3 speed Sturmey-Archer I had as a young teen.

A bike I actually found again recently after some 35 years! The college has it as one of their 'green bikes" students and locals can use for like a buck. Could tell it was mine as you could still make out where I carved a girlfriends phone number into it when I was 12 or 13. It's not a common bike here in the states.
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