How often do you change your brake fluid? I think the book says every 2 years? But do people do it that often? I last changed mine 4 years ago and have only covered 800 miles or so... Any thoughts on the subject?
2 years - the mileage is irrelevant, the stuff is hygroscopic so its best to replace it fairly regularly
I did it about 10 or 12 years ago I think - Goodrich. Make sure you get the right ones if you have an ABS car - they are a bit longer at the back I think.
Some say every six months. I read a study recently that documented the water percentage over time. As I understand it, damage does not occur until the fluid is about 4% water. Having said that, I have never noticed corrosion on brake parts less than eight years. After ten years, I have seen lots of issues. It is pretty simple to do and thus I am now targeting every five years for all my cars.
For what it is worth, the "Periodical Maintenance Operations" table (p 56 item 19) in the QV Owner’s Manual specifies "replace fluid every 6 months at least". The diagram on p 92 of the Owner’s Manual shows that the factory-specified receptacle for old brake fluid is a Chianti bottle. No, I do not change my brake fluid every 6 months.
Me neither - and for what its worth I've also never really understood how the moisture gets into what's basically a sealed system anyway! (Same as the whole issue with not using tap water in the coolant system. There is crap in it but unless you keep changing it very frequently, what there is is not going to be enough in one load of coolant to block anything. Saying that I still use water from my dehumidifier!)
Hot, bubbling brake fluid can release moisture into the system. That said, if you're not tracking the car, brake fluid should last a good long time.
It is well established that the water is absorbed right through the rubber parts. Seals and hoses. Tests have shown an average dilution rate at about 3% annually. 3% is enough to cause a substantial drop in boiling point. Dilution rate can be much more in humid climates. Different fluids have different absorbtion rates. As for the water in cooling systems, chemistry disagrees.
I think there is a small breather hole on the top of the reservoir, that could allow moisture / humidity in. If you were sufficient motivated you could probably fit a balloon filled with dry nitrogen over the hole...
Silicone brake fluid doesnt absorb water. I have used it on every car I have owned (mainly Lotus) but not (yet) in my ABS 328. I have never changed it once put in. Some people say thats a bad thing because it should absorb water that gets into the system. I cant see how water can get in even through rubber hoses etc if there is water-repellent silicone brake fluid on the other side though.
I know this probably isn't the best advice, but I tend to look at the fluid color. If it is getting darker and has 2 or more years of life, I'll change it. If it still looks clear like new, then I leave it alone. Many brake fluid caps are air tight and don't let much air into the reservoir. Also, if the car is driven hard or in dusty, wet conditions, expect to change it more often. When in doubt, change it. Brake fluid is inexpensive relative to repair or what happens with failing brakes.
I used to do mine every 2 years which was about 4500 miles. Pretty simple as I had SS lines that I did when I 1st got the car and installed SPEEDBLEEDER nipples on each caliper. Most work was removing the wheels . Then using a turkey baster sucked the fluid out of the reserve tank . Bled each caliper and filled system. One man operation took about 1 hour.
The negatives of silicon fluid are well known and have led most manufacturers and military services that did use it to discontinue its use. It is also why TUV wisely never approved its use.
All brake systems allow exposure to atmosphere, since constantly pumping brake fluid into the brake cylinders requires expansion and contraction, meaning displacement of the brake fluid in the reservoir. What makes up the difference in volume is outside air, which contains moisture. Would it be better to have some sort of sealed bladder that contracts and expands, instead, without letting in more moisture every time you use the brake pedal? Yes it would, but so far as I know no such system exists. Yet. Folks who live in a very dry climate such as a desert might have less of a problem in this area, but then again there's the heat issue, dryness affecting other components (leather, for instance) so... What changes the color of brake fluid is very teeny particles of rubber, being ground up by the very abrasive rust that occurs when water in the system combines with oxygen, acting on the cast iron cylinder walls. (It's really too bad that brake cylinders aren't lined with stainless steel as standard, but) ...This process occurs in the brake cylinders and slave cylinders. So there you have it, finely ground rubber seal material and some rust; makes a nice, icky grayish color. By the time you notice this appalling change in appearance it's already too late, and you most likely also have leaking seals, the rubber or neoprene having been slowly ground away. Another indication, of course is having to add brake/clutch fluid. It doesn't evaporate, so where does it go except through the ruined seals and corroded cylinder walls...? So far as the brake hydraulic system is concerned, the worst thing you can do is to let a car sit, mostly unused, without changing the brake fluid. Doesn't matter WHAT kind of fluid. Used or unused, change the brake fluid as recommended by the manufacturer. Every 6 months, two years, or whatever, up to you. As in the above quote, brake fluid is cheap...compared to rebuilding the entire brake system! Cheers, Rich
What Rich said. Also - depending on the car, letting it go for too long can be a mess. On an old BMW, the previous owner didn't do any of this work, and the paste created ended up seizing a caliper. On a Porsche 964 I had, the HP hydraulic system was almost ruined because the PO didn't do this work, and getting the paste out of that system was a pain. I do all my cars every 3 years.
I don't suppose anyone knows where I can get my hands on the plastic brake fluid resovoir, or give a substitute part? I'm going to replace my master cylinder and I'd like to be able replace it if I need to.
My 328 gets the fluid changed every year. I asked this question when I first got it, and the dealer and others that have experience working on the 328 said to do it yearly. So, it's part of the yearly service, with oil change. Would hate to have an issue with the brake components, and mine is a ABS car. Hope that helps?
