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All of the brake light switch comments reminded me of the huge controversy on other mailing lists over silicone (DOT5) v. non-silicone brake fluids. Back in my motorcycle racing days (er, 15 years ago now, how time flies), anyone on the mailing lists/newsgroups of the day would have been horrified by the idea of using DOT5. Much more recently (1-2 years ago), I found that most people in the old British car field are horrified by the idea of NOT using DOT5. Many religious flame wars ensued over this issue. As usual, the truth is somewhere in the middle, and it's something of a horses for courses thing. DOT3 and DOT4 are mineral-based brake fluids. DOT5 is pretty much always silicone-based. There's also a DOT5.1 which is apparently mineral-based or fully synthetic, but NOT silicone-based. There are also a good many other fluids which are off-the-chart in terms of performance, but legally fall into either the DOT4 or DOT5 classifications. Mineral-based fluids are relatively thin, and are hydroscopic. They like to attract and retain water. Over time (months to years, depending on climate), enough water will collect in these fluids to lower their performance (they boil at lower temps, and boiling fluids compress easily, so they lose their ability to transmit force from the master cylinder to the slave cylinders effectively). All that water also tends to cause lots of internal rust on any iron or steel brake components (the British particularly are fond of cast-iron in brake parts). They're also very nasty to paint. Get a drop of mineral brake fluid on paint it and will eat it up very quickly. Silicone-based brake fluids are relatively thick, and not hydroscopic. They're not destructive to paint. Because they don't attract water, they don't lose their effectiveness nearly so quickly, and they don't promote rust in brake parts. Sounds all rosy for silicone, yes? There's a catch, of course. Silicone, being fairly thick, aerates very easily. There are nearly always many small bubbles in the fluid. Getting ALL of the air out of the system is very, very hard. Air is very bad in fluid as it expands greatly under heat. It also compresses very easily. So, while DOT4 will eventually lose its effectiveness, the anti-DOT5 types insist that DOT5 doesn't work well out of the box (er, bottle). Most of the people who don't like DOT5 are people who insist on very high performance from their brakes (racers, generally). Most of the poeple who like DOT5 are people who let their cars sit for weeks undriven. Both are right, but often can't seem to see the logic of the other side. Oh, and if there are any plans to switch, mixing mineral and silicone fluids results in a goo that's nearly impossible to remove, and will happily block the small passages in many brake systems. You need to use lots of brake cleaner and flush out the braking system, or use all new parts, when switching from one fluid to another. __________________________________ Do you Yahoo!? Yahoo! Mail - Helps protect you from nasty viruses. http://promotions.yahoo.com/new_mail ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~