Brake Fluid Very Dark after 12 Months

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Irish Reiver

Irish Reiver

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10 Year
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Just over 12 months ago I completely overhauled my brakes. New OEM calipers, OEM hoses (except the 3 axle to body extended hoses which were Slee), OEM MC etc. At the time I deleted the ABS and the LSPV and took the opportunity to replace almost every brake line in the system. The intricate lines across the axles were all OEM and long lines front to back were just regular parts store brake tubing.

Today I noticed the brake fluid in the reservoir is super dark which surprised me given it was only a year since the overhaul.

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I always thought dark brake fluid was just old or a sign of deteriorating brake hoses. Obviously I will do a full flush over the next day or so but am I looking at some other issue with the brakes that I need to address?
 
Moving parts like the pistons in the calipers would collect brake dust that gets past the seals.
High heat on the pads, transferred through the components, thermo expansion.
That fluid doesn't look to bad. Can you dip some on a paper towel
 
What brand/type of brake fluid did you use to (completely) flush the system, same as before?
Reservoir cleaned out well before adding new fluid?
Reservoir cap on tight?

You can check the water content of the brake fluid with one of these:

 
Kernal said:
What brand/type of brake fluid did you use to (completely) flush the system, same as before?
Reservoir cleaned out well before adding new fluid?
Reservoir cap on tight?

You can check the water content of the brake fluid with one of these:

Click to expand...
I have the Prestone DOT3 fluid in the system. I bought one of the testers you mentioned just for gits and shiggles. I never knew such a tool even existed before. It will be interesting to see what it shows but either way the fluid will be flushed over the weekend.
 
I nearly have one. I purchased one on Thursday after @Kernal enlightened me about the existence of such a such a tool. Expected delivery is this afternoon. Will post some results later.
 
How long has it been since you replaced (rebuilt) the calipers? As @ppc said, they don't last forever.
 
Malleus said:
How long has it been since you replaced (rebuilt) the calipers? As @ppc said, they don't last forever.
Click to expand...
Brand new OEM calipers fitted in December 2024 so 16 months ago. Other than a few hard lines around the MC nothing from the original brake system remains. Only non-OEM parts are the Slee extended hoses.
 
Does that include the LSBPV? That thing is a trash hoarder. If not, I'd look into flushing the ABS pump.
 
Irish Reiver said:
Brand new OEM calipers fitted in December 2024 so 16 months ago. Other than a few hard lines around the MC nothing from the original brake system remains. Only non-OEM parts are the Slee extended hoses.
Click to expand...
It could be those lines by the MC. My F-150 had probably never had it's brake fluid changed before I bought it. The fluid turned green three months after flushing, then nine months after that, and then a year after that. It still turns green out by the calipers, but finally remains clear in the res.

This is evidently a by-product of the copper in the hard lines and the water in the hygroscopic fluid.
 
Folks, brake fluid doesn't circulate through the system. It is a static column of hydraulic fluid.
Caliper pistons don't retract. They simply float on the surface of the rotor unless your wheel bearings are loose or the rotor is horribly warped.
If all the lines were replaced and the system was flushed, there should be no contamination in the fluid.
 
The brake testing device pen arrived earlier and I get a reading of 3.4% water/moisture. Little pen flashes red which apparently means I have a problem. I'm with @jonheld on this insofar as brake fluid doesn't flow round the system so the test I just performed is only relevant to the fluid in my MC reservoir.

For comparison, I tested the brake fluid on the '95 LC which also has new calipers etc but still has the original LSPV and ABS system. The fluid was done on this one in January and is very clear. And would you believe it, it also registered 3.4%.
As luck would have it I still had one of the bottles of fluid that I used to fill the 95 a couple of months back and there was probably 1 inch of fluid in it. I tested it and got 2.3%.

I plan on flushing the '96 tomorrow which, without ABS and LSPV is a very quick job. I will measure the fluid on the bottle when I pull the seal. If nothing else this should give me some level of confidence in the tester pen (assuming it measures zero or close to zero on fresh fluid).
 
New sealed bottles of DOT 3/4 should be < 0.1% water to meet specs. Pen testers are OK for screening but can be off by a couple % or more.
I look at these pens more as a way to compare old fluid to new but not focus on the exact measurement ie: when measuring the same brand of Brake fluid.
 
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