Does synthetic fluid absorb moisture like conventional fluid? Sent from my iPhone using The H.A.M.B. mobile app
DOT 5 Brake fluids are Not Hyrgroscopic so they do not absorb water. These brake fluids are called Silicone, not Synthetic. The current DOT 3 and 4 brakes fluids are being called synthetic now, but in reality ALL brake fluids are man made (not found in nature) and therefore Synthetic. The difference is DOT 5 has to be at least 70% Silicone. While the others are Glycol based. Don't confuse Syhtetic with Silicone, and NEVER mix them.
A rule of thumb is this... DOT 3 absorbs 6% of its volume in water per year. So in 24 years without swapping it out or bleeding ... what do you have?
Putting a whole new brake system in my project. New lines, new m/c, using existing wheel cylinders. If I got to DOT5 do I need to rebuild wheel cylinders or just flush liberally?
Why was this type of brake fluid used to begin with? Is the water absorption a bug or a feature? If it wasn't absorbed and dispersed, it would pool in the lower areas and freeze solid, wouldn't it?? Aircraft have long used hydraulic fluid, though in a closed system. Why didn't auto manufacturers just use hydraulic (ATF)? Rubber components I guess. Just thinking out loud.
DOT5 compresses more than glycol and also more at higher temperatures. DOT3/4 is fine you just have to maintain it like anything else. If you don't drive a bunch you may want to flush it out regularly. Sent from my iPhone using Tapatalk
Where did you get this information? I have an electronic device that will determine the moisture content of glycol-based fluids. I test my cars every year and have found that it takes about 9 years for them to reach 2% moisture content, at which time I flush and change the fluid. How many 20+ year old cars out there are still running the factory fluid? A whole bunch, I'd bet.
One motorcycle manufacturer jumped into silicone fluid years back and probably created as many problems as they cured. Pretty much every car maker today recommends Dot 4. Dot 3 is an old standard but you still see it listed in service manuals - most quality brands list dot 4. There is also a Dot 5.1 fluid. Synthetic like Dot 4, high performance, low compressability listed for some modern cars and 'bikes. Will interchange safely with Dot 4. Dot5 is the odd one not mixable with Dot 3, 4. or 5.1. Condensation in a brake system with silicone Dot5 will form droplets on the bottom and will often slowly migrate to the ends of the pipes. Turns to steam when the brakes get hot - no pedal. For this reason systems with silicone fluid should have the fluid changed every two or three years, same as systems using glycol or synthetic fluids. Some years in the brake industry teaches a few things. Garpo
Planned obsolescence......if they wanted you to keep your new car for 20 years, they would probably use silicone in the cars they sell.
No, not planned obsolescence. Silicone has many disadvantages, the biggest is not being compatible with ABS brake systems, common/std. on vehicles for over 20 years. Cost would be another.
I was taught @ Henry Ford CC Auto Tech Program 6% per year on average open atmosphere . Either way Dot 3 is not my first choice... The point here is... Moisture is bad...
I think guys like to use silicone fluid as it doesn't eat paint. Regular dot 3 does. I only use silicone on my Harley. I stick with dot 3 on my old cars, but I do flush it out a lot along with all other fluids kinda overkill but I like the piece of mind that I have new fluid all the time. Old cars weren't made to be maintenance free like some new cars are. Hell new vw's you can't even change the transmission fluid.
My grandfather used to park his 66 impala and 62 corvair for years on end in a field and the brake fluid never got changed I'm sure. Sent from my iPhone using Tapatalk
I've been running DOT 5 in my 64 Impala for 17 years now. Brakes work just as I would expect. I've had dozens of cars in that time that I used DOT 3 with no issues either. That being said I plan to use DOT 3 in any new builds just for the convenience of it being readily available when you're on the road. It's a pain keeping DOT 5 around for the one car. Just my $.02.
If you spill brake fluid (or anti freeze) on paint work, simply flush with water. When doing a brake job it is often a good idea to do this anyway, just in case there is an odd splash. Brake fluid loves water. Any reaction with paint is slow, but a quick wash off saves the paint. Silicone does leave a residue on paint - can cause some extra work when re painting. Garpo
I wonder why they don't bypass all the problems with conventional brake fluids and use hydrocarbon based hydraulic fluid, i.e., transmission fluid. Is not hydroscopic, won't eat paint, won't contaminate surfaces so pant won't stick, et., etc., etc. I know the usual rap on it is it swells brake system rubber. Simple solution; change to the rubber used in auto trannys. They run hot hydraulic fluid for a hundred thousand miles with no swelling and good performance and they are packed with rubber seals. Incidentally the glycol based fluids are great for stripping paint off plastic models. Won't attack styrene but eats the paint off over night.
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