Last week I changed my brake pads and had my rotors turned. When I went to drain some of the brake fluid from the resevoir, it was black. I noticed this problem about a year ago when I was bleeding my brakes. I had serious amounts of rust come out of the system then, but I thought I'd cleaned it up pretty well. Now I see that I'm going to have to take a more serious approach to the problem. Aside from changing the hoses and rebuilding the calipers, is there anything else you guys think I should do?

 

If you're not using silicone fluid you could try draining the system and flushing it with denatured alcohol to clean out the lines.

 

I appreciate the tip, but I'm curious, why can't I flush the system with alchohol if I use silicone fluid?

 

Silicone brake fluid and alcohol won't mix.

 

As the "king of brake fluid" for the past year or so, I noticed the same thing right after I put my rear discs on. I still had insufficient braking (see my message below about fixing my '84 brakes with the GM recall kit), so I tried bleeding them again- and the fluid was discolored, after only a few weeks. Three or Four bleeding episodes later, including the latest one, the fluid is pretty close to being clear. The master cylinder holds a lot of fluid in the quick-take-up valve, and the new fluid might've helped to dislodge old contaminants.

Apeiron, if the system was flushed with denatured alcohol (where the hell is that found, anyway? Is that rubbing alcohol?), how would you re-introduce new brake fluid to the car? Or, would you have to flush the system out, and blow air thru each line, wait for it to dry, and hook the whole brake system back up?

 

Yeah you'd have to blow the lines clear, or at least give the alcohol time to evaporate. Denatured alcohol is ethanol mixed with things like methanol or isopropanol. You can usually get it at a hardware or drug store. I don't see why you couldn't use another alcohol like isopropanol. Rubbing alcohol might not be the best to use though, since it's usually only about 70% isopropanol, with the rest being mostly water with a little glycerine mixed in.

Actually I see now that isopropanol cleans up DOT 5 brake fluid, so it might work with other silicone based fluids.

 

I'd be a little worried that the alcohol would have an adverse affect on the rubber hoses and seals. I take it though, that you guys haven't noticed any problems after the alcohol flush?

Denatured ethanol can be purchased at industrial supply houses. It is something machine shops keep around for general cleaning, degreasing, etc. I think its relatively cheap, too.

 

Thanks for the info Apeiron. Any advice on the best way to flush the system?