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Newb inquiry here. Just doing a routine check up on my mazda 3. Question is re brake/clutch fluid reservoir. I saw some tiny black particles/dirt inside the reservoir. But when I shook the reservoir inside it just mixed with the fluid. Is this normal? Thank you
 

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Mazda "E" Division
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Good brake fluid is a light amber colour. The brake fluid colour gets dark slowly to a bad black colour.
It's a sealed (closed) system and should never have contaminates inside. The best thing is to do a brake fluid flush, which could prevent more expensive repairs.

A brake fluid flush will empty all the reservoir/lines.
 

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I change out the brake fluid in the reservoir once-twice/yr. It is NOT sealed. It has to take in air from the atmosphere as fluid goes down when the pads wear. Air has atmospheric water in it, which the brake fluid LOVES.

Then about every 5 to 7 years, I bleed the brake calipers (or have it done now) to flush the old fluid out (filling the reservoir with fresh fluid at start and end of this).

We had an 1983 Benz that we kept for 25 years. I could always tell when its calipers needed bleeding/flushing. The left rear one would start to drag slightly.

Ralph
 

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There shouldn't be any particulates in the reservoir. The brake fluid should be replaced and the system flushed completely every couple years, especially if you live in a place that has high humidity. The system is not air tight, and as brake fluid is hygroscopic, it will suck moisture out of the air. This moisture will eventually contaminate the fluid to the point where it no longer functions properly. Its very simple to check the fluid using a small testing device available at many auto parts stores. Once you get up to about 2% moisture content its time to flush and refill.
 
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