Brake Fluid ID
I was checking the fluids on my '67, and noticed the front chamber of the dual MC is a little low. I was going to top it up, but then reading through the archives it sounds like a disaster if you use the wrong brake fluid, DOT 3, 4, 5 and mix. I don't know what it has, could be original like DOT3 or a silicone replacement like DOT5. Is there an easy way to feel, smell, or see the difference? Thanks for any tips.
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Big Tanks In the High Mountains of New Mexico -
Re: Brake Fluid ID
Michael------
Remove a few ounces of the fluid. Place it in a clear small glass jar or vial with a lid. Add some fresh, known DOT 3 or 4 fluid to it. Shake the jar and let it set for 1/2 hour, or so. If there is a phase separation (i.e. like "oil on water"), then the fluid in the master cylinder is DOT 5 silicone-based. If there is no phase separation (i.e. the fluid appears to be completely homogeneous), then the fluid in the master is either DOT 3 or DOT 4 glycol ester-based fluid. There is no practical way to differentiate DOT 3 from DOT 4, but it's not necessary. Those fluids are compatible, so you can fill with either one.In Appreciation of John Hinckley -
Re: Brake Fluid ID
Just in case it's DOT 3, do not get any on you paint. It will start to dissolve it quickly.
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Re: Brake Fluid ID
Michael,
Dot 5 silicone brake fluid is dyed purple to differentiate it from dot 3 and 4.
Dot 5.1 is a synthetic non-silicone brake fluid which I understand is amber in color. I know nothing else about dot 5.1.
I would suggest if it is not purple refill with dot 4.
Joes test is the best indicator of compatibility.
Bruce BComment
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Re: Brake Fluid ID
OK, thanks for the tips. The fluid in the MC mixes well and quickly with DOT3, so no separation at all. And both have the same distinctive smell. Other than a slight amber color to the fluid in the MC (which I understand is a normal color change for fluid as it ages and sits), the DOT3 and the existing fluid look the same too. So guess it is DOT3, thanks again.Big Tanks In the High Mountains of New MexicoComment
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Re: Brake Fluid ID
Bruce-----
Out-of-the-bottle, the DOT 5 silicone fluid is purple. However, in my experience it quickly changes color to yellow after it's used. The yellow is a deeper yellow than the very pale yellow that DOT-3 is usually seen as. However, in a master cylinder it's hard to tell them apart.
I think the purple color of the DOT 5 must be a dye which turns yellow as a result of some influence, likely heat.In Appreciation of John HinckleyComment
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