Date: Mon, 16 Mar 1998 02:34:09 GMT From: joenopsamoresource.com (Joe Way) Subject: Re: silicon brake fluid
On Sun, 15 Mar 1998 19:48:53 -0500, geostarnopsamsshub.net (Geo) wrote: >I'm thinking of putting in silicon brake fluid because it doesn't absorb >water like glycol fluid. Are there any negatives? > >-George ==== Well, my Internet friend Jim Forbes has put me on the spot here. OK--get ready for more than you wanted to know (maybe) about silicone fluid. This is most of a message I wrote to the oletrucks mail list, so it isn't 100 percent in context here; but it doesn't miss by much. I'm too lazy to edit the whole thing right now, so here it is as written. ====Jim Forbes said in response to a question about how water gets into a brake system: > > When the system warms and cools with the change in temperature every day, > air from the atmosphere is drawn into and out of the master cylinder > reservoir, thru the vent. The amount of moisture collected this way is > small, but adds up over a period of years. Note that all dual master > cylinders, and most single cylinders made starting in the 60s, use a > diaphram between the cover and the vented area, to keep out moisture. Old > trucks are different (assuming it's the stock master cylinder)...the vent > is > simply a hole and baffle in the cap. The newer master cyliners will keep > out moisture, the original cylinders will allow it to enter thru the vent. > I think this is why old trucks (and cars) from the 50s and earlier often > need the wheel cylinders replaced. > ====Joe says Jim is absolutely right here, and this is *very* important. But it gets worse--moisture will migrate through the brake hoses, and will pump in around the seals in the cylinders with every stroke of the pedal--regardless of the type of fluid. Some people think that because DOT5 is not hygroscopic it can't get water in it. But that just means it does not actively seek to combine with water. Water *will* get into DOT5 even in systems with sealed caps. It tends to aggregate into droplets. If the droplets settle somewhere other than on a cylinder bore, no problem. But if they end up in a cylinder, especially on a car not driven where the drop (which is heavier than DOT5 fluid) just sits there, they can cause worse problems than in glycol fluid. ==== > I agree that silicone fluid is probably not as bad as regular fluid at > trapping moisture. I did use silicone in my 39 Chevy street rod, which I > had for 5 years, and no problems. But, the added expense, and the > possibility of adding the wrong fluid weigh against using silicone. Also, > regular brake fluid works fine with just a little maintenance. > One other thing about silicone fluid--it will not "eat" paint like regular > fluid, which is good. Conversely, if you have not yet painted the truck, > and silicone fluid spills on a surface that you want to paint, it is > difficult to remove the silicone from the surface. The silicone will keep > the new paint from sticking. A friend ran into this problem on his street > rod, he had spilled some of the silicone fluid on the fender, and later had > the car painted. A large patch of paint peeled off the fender in that > spot. > Of course, he didn't go to great lengths to clean the surface before > painting, as he didn't realize there would be a problem. > > >I did forget one important point - the silicone fluid can not be used with > >ABS systems. I don't know how many oletrucks have been outfitted with ABS > >though - I suspect none to few. > > Probably none. > > Jim ====Joe says Those with pressure-operated brake light switches should keep in mind that DOT5 is known to be *very* hard on electrical contacts. Some owners(mostly of German cars, it seems) report switch failures annually using DOT5. I believe but haven't been able to confirm that this problems with electrical contacts is the reason ABS manufacturers prohibit DOT5 from their systems. Another poster had this to say about air in DOT5: "The only negative characteristic I've ever heard about silicone brake fluid is that if the brakes are bled at lower altitudes and then driven up to "high" altitudes there is a chance that the entrapped air that was not problem at lower elevations will now manifest itself in a spongy brake pedal or worse. "This situation won't effect most people and if one anticipates such a situation they can bleed the brakes at a high altitude and solve the problem." ====Joe says This problem does not involve air in the form of bubbles, but rather distributed throughout the fluid on a molecular scale. It cannot be bled, regardless of elevation, because it is distributed uniformly throughout the fluid. The instructions on DOT5 are very specific about taking care not to shake the container or pour from a height, to avoid aeration. Driving to the higher elevation lowers the ambient pressure, causing the air in the fluid to expand and giving a mushy pedal. One person I've corresponded with on this issue was involved in the Pike's Peak hillclimb the year a number of racers showed up with silicone. He told me they made it about 1/3 of the way up the hill and had to be towed down because their brakes had failed. When I used to set up at the Reno Swap Meet during Hot August Nights I could always count on half a dozen guys wanting to know why they all of a sudden had a soft pedal that went nearly to the floor. I'd say, "let me guess-you run silicone fluid?" Yep. Another particularly telling point for me is that--so far as I have been able to determine--no manufacturer other than Avanti II has ever installed DOT5 fluid in a standard production car *regardless of cost* at the factory. Yes, I know that the military and the USPS specifies DOT5, but those are fleet purchases rather than standard production (I'm not sure Avanti II should count as a standard production car, for that matter). I've been told that some military commands have returned to glycol fluid, but haven't been able to confirm it. I can confirm that many of the small fleet managers among my customers who tried DOT5 have returned to glycol. I invite anyone who knows of any production car that was filled w/DOT5 at the factory to e-mail me. This inquiring mind wants to know. (Don't bother telling me about Harley Davidson-I want cars and trucks.) If DOT5 was better the expensive cars would have had it, at least pre-ABS. The question of race cars came up in another post. I've corresponded with several racers and mechanics on this, and all of them tell me that premium grades of DOT4 (British type glycol) are the preferred fluids. This is not to say that *no* racers use DOT5; just that I haven't been able to identify any. I do know that Wagner is sponsoring a team (Winston Cup, I think) that uses their premium DOT4. The effect of fluid on rubber was mentioned. The first DOT5 fluids performed very poorly because they had no effect on the rubber. DOT specifications carefully call out the properties that brake fluid must have, and one of the requirements is that it cause expansion of the rubber parts by about 10-15%, and the rubber manufacturers, also subject to strict DOT specs, count on this when they formulate their parts. The early DOT5 didn't do anything, so they combined additives. Took them a while to get it right, and many in the industry don't agree that they have. But get this--there are two types of rubber used for brake seals. I just spent 20 minutes looking for the industry publication I have with the names, but can't find it, so will have to generalize. DOT5 additives are formulated to work with the newer material used to make parts for later model cars. They are not formulated for nor do they work properly with the older material from which the parts for the trucks you guys are driving are made. In a thread on this subject in another forum someone said DOT5 must be good because they use it in airplanes. I went to the airport and talked to the people at an FAA certified repair station. They showed me aviation brake fluid-a petroleum based fluid a lot closer to ATF than to auto brake fluid of any kind. It does happen to be about the same color as DOT5. If your car or truck has a Midland brake booster or similar type, be advised that these boosters have a reaction port or control valve which has brake fluid under pressure (during brake application) on one side and engine vacuum on the other side. If the seal on the control valve piston fails, fluid will be sucked into the engine and burned. Be further advised that one of the byproducts of combustion of DOT5 fluid is a *very* aggressive abrasive which will lunch an engine in short order. Typical American later model (say, roughly, 1960 & later) master cylinder/booster combinations such as are sold for retrofitting into OleTrucks don't have this problem. Before someone scolds me again for taking commercial advantage of the list, let me state that I do not sell or manufacture any kind of brake fluid, nor do I have any connection with anyone who does other than having friends who work at parts stores. It's just a subject that I'm very interested in, that I have researched at some length, that is important to my customers and their safety. Most of the above is fact, not opinion. Most of it I can substantiate with competent documentation, given time to find the original materials in my piles of stuff. Most of it is commonly known in the brake rebuilding industry. I believe I have identified all the areas in which my research is incomplete or I'm making an educated guess. If you want my opinion, here it is: DOT5 fluid is great for trailer-queen show cars that are never driven on the road. Any vehicle driven frequently enough to be called a "driver" should have glycol fluid, flushed *at least* every other year and preferably sooner. Joe ==brake cylinders sleeved with brass== ==One-Wire conversions and rebuild kits for GM alternators 1963-85== ==Quincy, CA==
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