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To Silicone Brake Fluid Or Not?


Bingster

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I know this site has been around this block before, but as I am getting ready to put my brakes back together, what again are the pros and cons of using silicone fluid?

I am replacing most of my lines and all wheel cylinders plus the master.

Was there an issue about it attacking rubber components?

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I have used silicone in 5 vehicles no problems. I do replace everything lines, hoses, all cylinders. No problems over 5 years. I see you say you are replacing most of your lines not sure why you are keeping some old lines but be sure to flush out the old lines well.

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I have used silicone DOT 5 for 10 years in 5 or 6 cars. It is a good choice and will not attack your paint like DOT 3. It will not attack the rubber components. I have DOT 5 in my '37 Ply. and '66 VW.

I know this site has been around this block before, but as I am getting ready to put my brakes back together, what again are the pros and cons of using silicone fluid?

I am replacing most of my lines and all wheel cylinders plus the master.

Was there an issue about it attacking rubber components?

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Share on other sites

I am not as keen on the DOT5 silicone. If everything has not been replaced (in other words, no DOT3 in there at all) you risk generating gummy clots because DOT5 and DOT3 are not compatible. You need to have every single drop of DOT3 flushed out before you add DOT5.

I have seen systems where DOT5 was introduced with some DOT3 still in there. It is not pretty.

DOT3 absorbs water, inhibiting rust. DOT5 does not entrain water. (The water can even be from moisture in the atmosphere, since these systems are vented to open air.) This can promote internal rust, especially in cars driven less frequently (moisture bubbles sit in one spot).

Yes, DOT5 does not bubble paint, but so what? Are you that sloppy when you fill and bleed the system? :)

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after many years of frustration with DOT 3, I have converted both of my cars to DOT 5 silicon. I love it, and would not have it any other way.

since I don't drive my cars often, Dot 3 would rust out my wheel cylinders very quickly causing leaks which would then ruin the paint. Now that I have switched to dot 5 I don't have such problems.

the metal lines can be reused if you flush them with alcohol (wood alcohol or denatured can be used). Some even have had luck reusing all the rubber parts, but they need to be washed very good.

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after many years of frustration with DOT 3, I have converted both of my cars to DOT 5 silicon. I love it, and would not have it any other way.

since I don't drive my cars often, Dot 3 would rust out my wheel cylinders very quickly causing leaks which would then ruin the paint. Now that I have switched to dot 5 I don't have such problems.

the metal lines can be reused if you flush them with alcohol (wood alcohol or denatured can be used). Some even have had luck reusing all the rubber parts, but they need to be washed very good.

To each his own; DOT5 is an approved product. But 'does not ruin paint' is not, IMHO, why you select a brake fluid. Gasoline is also hard on paint, but somehow we manage the risk. DOT 5 is fine but you must be aware of the implications, which tie to inability to keep moisture in suspension, and a severe incompatibility with any remaining DOT 3.

Since DOT 3 keeps water in suspension, it should provide better resistance to rusting. DOT 5 will allow puddles of moisture to form, which can provide localized pitting. Millions of rust-free DOT 3 systems exist on this planet.

You are correct that you must be VERY thorough when flushing. Every teeny tiny drop of DOT 3 must be gone from every nook and cranny. This is not easy to accomplish in an extant system. If you are starting from scratch with all new master, wheel cylinders, lines and hoses then no problemo.

I know someone who added DOT 3 to top off his DOT 5 custom motorcycle. It was a very expensive mistake.

To anyone contemplating the switch, mix a little DOT 3 and DOT 5 together and see what happens. :)

The good news is that to do it right, you replace everything, and that is not such a bad idea for a 60 year old hydraulic system. Then, you simply make sure that no one ever tops off your system with DOT 3. :)

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My 47 Chrysler Coupe , has all new steel lines, rubber hoses, wheel cyls, rebuilt MC, and I have beenrunning Dot 5 ever since, very happy with it in my new and clean system.

The Dot 4 is very good for Disc and ABS braking systems, don't think it would be necessary for a 60 YO Mopar that has Dot 3 in it's system already.

Yes brake system must be be purged of it's dot 3 completely or else new lines, and parts will be the only way..........Fred

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The dot 3 is clear the dot 5 has a purple color tint

Yes, DOT 3 is clear. But usually brown or even blackish in an older system. DOT5 is a nice purple. It is unlikely that anyone changed your old car to DOT5. If you are not sure, dab some on a rag and puddle it on some scrap metal painted with enamel. If the paint bubbles up it is DOT 3.

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