some info from snowbum's site ....... it should apply to ALL vehicles
Brake fluids:
Use ONLY DOT3 or the slightly better DOT4. Keep it OFF the paintwork, and keep a VERY WET RAG on your paintwork when working with it. If, HORRORS!.. it gets on the paintwork, wash it off with water, INSTANTLY...that means RIGHT NOW! You do NOT have 10 seconds! ALWAYS have a WET RAG instantly available when using brake fluid!
Don't use "race" fluids...they require changing once or twice EVERY year without fail, and offer NO advantages to a street bike. There are so-called 'premium' DOT4 fluids; some are called RACE fluids; and there is also, confusingly, a DOT 5.1 that is NOT silicone based and hence is usable...but WHY?
I recommend inexpensive DOT3 for most folks who want the cheapest, and who do change fluids EVERY year and are not overly hard on brakes, with DOT4 for those who are hard on the brakes, getting them VERY hot. It IS BEST to change brake fluid yearly. I personally do it as part of my pre-Winter service. For longest brake system life, your brake fluid really needs yearly changing, as it attracts moisture, right through the non-leaking lines, molecular sized holes in everything....especially the master cylinder bolt and screw fastenings, etc. Bleed the brakes until clear fluid comes out. Best to use a fresh 8 ounce can each time; but not as much of a must as some say...just don't leave the cap off for appreciable amount of time.
If you regularly change fluid by the full bleeding method, until fluid is nice and clear, then you are UNlikely to EVER have to replace the master cylinder or calipers or brake hoses. If you DO open a system, for such as rebuilding a caliper, or changing a hose, use only brake fluid or specific brake cleaner, for cleaning parts. For very serious caliper overhauls, etc., you COULD use other solvents, heck, even detergent and water...but after drying, any reassembly means using brake fluid for lubrication of parts during assembly, ETC.
In MY opinion, the absolute limit for brake fluid changing for a bike with very MINimal use, is 18 months. Those who ride in a lot of humid weather, or who ride a lot; if the bike is parked in the sunlight, etc., might even consider 6 month fluid changes. Fluid is VERY cheap compared to new parts!
NEVER use DOT 5 silicone fluid in your BMW braking system...NEVER! DOT5 silicone fluid does not absorb moisture, so it allows moisture to condense into droplets in your braking system and thereby probably rotting it out faster; and it can, in freezing weather, FREEZE the brakes! In most situations yearly bleeding will NOT get trapped moisture out of a silicon fluid system. Silicon fluids are also generally not compatible with the rubber parts in your bike's braking system (depending on year of seal manufacture, and if Brembo or ATE). DOT5 silicone fluid has no advantage for airheads. Silicone fluid is thin, so you MIGHT think that it is easier to bleed on an opened system...but, the truth is that silicone brake fluids tend to get millions of tiny bubbles, defeating that idea; and, won't absorb water...but water gets inside from various means, and forms globules, and corrodes the parts! At very elevated temperatures, silicone gets compressible!.....a BAD thing. Yes, there ARE reports of folks using silicone brake fluid for years in Airheads, with no problems. I suspect that there are various types of rubber parts in the system in use over the years. Brembo themselves has always used 'natural rubber' (per Brembo) that is not compatible with silicon fluid. That is how it probably STILL is. I am unsure on ATE calipers. Best not to be a Test Rider.
Remember: moisture droplets can do REAL FAST damage, but small to moderate amounts of moisture dissolved in DOT3 or DOT4 acts so slowly that yearly fluid changes really do work well! The moisture does NOT dissolve in silicon fluids, it collects in droplets that increase their size slowly, and they can do real nasty damage.
Last edited by carolines truck; 01/19/2009 6:22 AM.
