DOT 5 4 3

Not a cold winter oil thread just a hot summer fluid one. Its over 100'F around Trixie in garage this week and discovered brake fluid jetted out the end of master cylinder in 8" long canoe shaped puddle at least a foot beyond straight down by gravity, which had a 6" round slash puddle. Its leaked twice before but Hylomar stemmed it for a couple seasons in a row. Thought I'd fixed it today to discover the toothed boot washer had fractured so lost its grip. I got Trixie brake plenty hot tagging behind hot rods but never lost any brake fluid to matter. Trixie gets DOT 3 and Peel got DOT 4 just because.

http://www.advancepetro.com/differentbrakefluid.htm

Im curious, anybody using DOT 5, the silicone stuff?

I use DOT 5 as that was what I thought was the only fluid compatible with the rubber parts.

I have used dot 5 for over 15 years,flushing it yearly,with no problems.I have read recently that Lockeed did not
want it used in their systems.I always liked it because it did not dissolve paint.I am watching this thread as to the
pros and cons of this as I am not a fluid specialist.I know they dont want you to use it with ABS systems,But that
I understand why on that front.
YING

Something I gleened from the internets.

The Brake Fluids are available in various colours like Brake Fluid DOT 3 is available in clear, Pale Yellow, Blue & Crimson Red colour, similarly brake fluid DOT 4 is available in Clear, Pale Yellow & Crimson Red colour, brake fluid DOT 5.1 is available Clear, Pale Yellow & Blue colour. Brake Fluid DOT 5 is available in Purple & Violet colour so colour is not a criteria to distinguish between the different types of brake fluids. The color is added in brake fluid to detect the leakage easily and color does not effect the quality of brake fluid.

DOT 3: This brake fluid is a poly glycol base product. Its dry boiling point (ERBP) is 205°C minimum and wet boiling point (Wet ERBP) is 140°C minimum. It absorbs 1 to 2 percent of water per year depending on climate and operating conditions. It is used in most domestic cars and light trucks in normal driving. This brake fluid does not require cleaning the system and can be mixed with DOT 4 and DOT 5.1 without damage the system. This brake fluid absorbs moisture from the atmosphere thus reduces its boiling point (ERBP). It can also damage the paint on a vehicle.
DOT 4:This brake fluid is also based upon poly glycol. Its dry boiling point (ERBP) is 230°C minimum and wet boiling point (Wet ERBP) is 155°C minimum. It is used in medium and higher size of modern cars; and also for vehicles in high-altitude, towing, high-speed braking situations or ABS systems. This brake fluid does not require cleaning the system and it can be mixed with DOT 3,DOT 5.1 without damage to the system. This brake fluid also absorbs moisture out of the atmosphere thus reduces its boiling point (ERBP). It can also damage the paint on a vehicle. The modified poly glycol boric ester DOT4 brake fluid is also available.
DOT 5: This brake fluid is based upon silicone. Its dry boiling point (ERBP) is 260°C minimum and wet boiling point is (Wet ERBP) 180°C. It is used in applications, like for weekend, antique, collector cars that sit for long periods and for some military vehicles. Some car manufacturers are also used in their road driven vehicles. This brake fluid does not mix with DOT 3, DOT 4 or DOT 5.1. It will not absorb water and will not damage the paint on a vehicle. It is also compatible with most rubber formulations. It absorbs more air and giving poor pedal feeling. It is unsuitable for racing due to more compressibility under high temperatures. If as little as one drop of water enters the fluid, severe localized corrosion, freezing or gassing may occur. This can happen because water is heavier and not mixable with silicone fluids thus it is unsuitable for ABS.

DOT 5 fluid is highly compressible due to aeration and foaming under normal braking conditions, providing a spongy brake feel. Poly glycol type fluids are 2 times less compressible than silicone type fluids, even when heated.
DOT 5.1: This brake fluid is also based upon poly glycol. Its dry boiling point (ERBP) is 260°C minimum and wet boiling point (Wet ERBP) is 180°C minimum. It is used in severe-duty vehicles such as fleets and delivery trucks; towing vehicles, and racecars. It can be mixed with DOT 3 or DOT 4 without damage to the system. It maintains higher boiling point than DOT 3 or DOT 4 fluids. It is excellent for severe duty applications particularly for racing of car. It also absorbs moisture out of the atmosphere and thus reduces its boiling point. It can also damage the paint on a vehicle.

The sillycon 5 stuff is mostly used in long stored craft such a military and museums because it don't attract water like the others BUT moisture still gets in to condense over time to settle in a puddle in a hose of caliper then can rust up or freeze up or boil up in desert down hill usage. Its compressibility means its not good for racing or other serious braking control feel. I some cases the seals are not compapable with sillycon. Its not found in off the shelf stores either.

DOT 5 silicone brake fluid is 3-5 times more compressible than DOT 3. Recreational riders will never see this difference, as the system compressibility is dominated by the hydraulic lines (watch 'em move as you squeeze the levers) and the internal rubber seals. Riders who spend their motorcycle time on the edge may feel more comfortable with the conventional fluids. Certainly in vintage car circles, DOT 5 is the overwhelming choice of owners due to its kindness to painted surfaces and its storage time (the fluid is hydrophobic and can be kept on the shelf or in the brake system for many years). The fluid will froth when strongly agitated in a partially filled container, but this disappears after a few minutes. Absent a large amount of air in the brake system, it's hard to imagine frothing as a problem in situ, although I'll defer to Steve's opinion if he has evidence of this problem. For us hobbyists and recreational riders, I believe that DOT 5 is the product of choice; I use it in all of my British iron. As others have stated, DOT 5 is absolutely incompatible with other brake fluids, and can only be introduced into a purged hydraulic system. Its biggest negative is its cost. DOT 5 is available at all of my favorite local automotive stores in Seattle and Austin.

OH cool Rick, I didn't know if Lockheed seals and hoses ok with DOT 5 but sure know I've had wind blown leaks for paint damage from the others. Can't imagine street conditions revealing a loss of brake feel-control as you assure us it don't. Only thing I've heard about silicon and paint is once surface silicone exposed its very hard to remove so any paint will stick afterwards.

Roger the problem of painting over a siliconed surface, Steve. I had a small area on a tank I was preparing, and it took a long time to get to the point where the primer didn't fisheye. OTOH, I got a few drops of DOT 5 on my Norton tank, but since it didn't attack the surface, it cleaned up nicely. Polished out well, too. I'm sure a microlayer of DOT 5 is still there under the wax.