What's in my brake fluid?

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Jul 14, 2020
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I just noticed this when checking all my fluids the other day. This is after sitting all night, -22 degrees Celsius outside, slightly warmer in the non heated garage. I noticed it a few days ago though and it was only minus 10. Was not visible when I tried to show my friend who's a licensed mechanic, on our lunch break. Truck was warm as we'd been driving it for work.
Edit: forgot to mention it was flushed less than a year ago about 20,000kms ago. Was original fluid from 2005 before that. No issues with the brakes or abs ever so far. 2005 Silverado with 218k miles.
 

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Water does seem the most plausible. I did plan on flushing it again in the summer, but now it looks like that is going to have to happen sooner. A tech I used to work with did it (with me right there in his garage) on a weekend while we were replacing a bad wheel bearing.
We didn't get all the fluid at the time, as one of the bleeders felt like it might break and we didn't have a replacement wheel cylinder handy. I planned to just flush it early again since it was so overdue at the time.
I don't believe we cleaned the reservoir out at the time.
I think I will get a fluid extractor and just empty and refill the reservoir a few times as I don't have the fancy brake flushing tool the tech foes
 
Should look a little something like this after cleaning,

View attachment 83672
Now how do you do that without dirturbing damaging contaminants into the braking system? When I had my valve cover off and cleaned some sludge from the head I was told I shouldn't have done that, for this reason. This seems more risky than that did imo.
 
Not sure what's in there, but pretty sure it hasn't to be there.
I'd have a thorough flush or even consider removing and cleaning or replacing the MC.
 
On a few years newer Silverado, I think just 2 roll pins hold it on,

View attachment 83681
I'm just going to suck it out and replace it, drive it and repeat a few times temporarily until spring and then I'll do that plus get a wheel cylinder for the one rear in case it breaks, and I can flush that corner too. It's too cold to be working on more than I have to right now. I work in the cold Monday to Friday but I get paid for that. The weekend is my thaw out time.
 
I'm just going to suck it out and replace it, drive it and repeat a few times temporarily until spring and then I'll do that plus get a wheel cylinder for the one rear in case it breaks, and I can flush that corner too. It's too cold to be working on more than I have to right now. I work in the cold Monday to Friday but I get paid for that. The weekend is my thaw out time.
Alternative without removing the reservoir is to suck out the fluid and spray some brake cleaner on the inside walls to wash off the grime. Add some brake fluid to mix it up and suck that all out. Repeat a few times. Ideally you do this right before a brake fluid change.
 
Get something like a MityVac that is pressurized, MityVac has a brake attachment just to do this.
I think I'll do that long term, but right now something along the lines of a turkey baster is in the budget. Lol. That and some brake cleaner and brake fluid. I'll do that tomorrow and post the results.
 
Alternative without removing the reservoir is to suck out the fluid and spray some brake cleaner on the inside walls to wash off the grime. Add some brake fluid to mix it up and suck that all out. Repeat a few times. Ideally you do this right before a brake fluid change.
Bad idea on the brake cleaner. Brake cleaner is for rotors and will contaminate the brake system if sprayed into the master cylinder.
 
Brake cleaner evaporates quickly, and you spray it in the reservoir, not the master cylinder.
But the reservoir is connected to the master cylinder, there is no way on earth you're going to spray it into just the reservoir without some of it draining down into the master cylinder.

Plus brake cleaner is a mixture of short-chain hydrocarbon solvents and no way I want any of that coming anywhere near the seals under the reservoir nor the seals in the master cylinder. One should never ever get hydrocarbon solvents anywhere near brake component seals.
 
But the reservoir is connected to the master cylinder, there is no way on earth you're going to spray it into just the reservoir without some of it draining down into the master cylinder.

Plus brake cleaner is a mixture of short-chain hydrocarbon solvents and no way I want any of that coming anywhere near the seals under the reservoir nor the seals in the master cylinder. One should never ever get hydrocarbon solvents anywhere near brake component seals.
I didn't take the risk on the brake cleaner. Just sucked out the reservoir and refilled it. Will do it again this summer and flush the one back that wasn't done, once I have a spare wheel cylinder.
 
But the reservoir is connected to the master cylinder, there is no way on earth you're going to spray it into just the reservoir without some of it draining down into the master cylinder.
Then just take off the reservoir. It takes a little work but no way I was going to change the brake fluid on my 95 Skylark and leave all the junk coating the walls. Just annoyed that nobody will see the results like they would if the reservoir was made of clear plastic instead of this black stuff.

IMG_4218.jpg
 
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