Brake Fluid Question

Nick Bernier

Nick Bernier

Member
I don't know the history of my '40 Deluxe Convertible, but I found a note in it saying the brake fluid was changed to silicone brake fluid. Would that be the same as DOT 5? Should I flush the whole system and start over?
Thanks,
Nick
 
If your brakes are good now, you've got an upgrade, why change it back? The advantage of silicone is that it doesn't absorb moisture. The downside if any, is it's easy to homogenize when adding or bleeding, which gives you spongy brakes.
 
ford38v8 said:
If your brakes are good now, you've got an upgrade, why change it back? The advantage of silicone is that it doesn't absorb moisture. The downside if any, is it's easy to homogenize when adding or bleeding, which gives you spongy brakes.
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And..... it has a tendency to want to leak in places that normally DOT 3 and 4 do not.
And, another note regarding color... purple is not the 'magic identifier'. I have been using DOT 5 that is more 'yellowish'.
Having said all this, I have had DOT 5 in one of my vehicles since 1989. No problems.
Identifier... I'd probably trust the note. But, if you want, spoon or suck out a teaspoon worth, and try to mix it with water. (in a glass). Do the same with DOT 3 or 4. You should readily see the difference.
 
The brake fluid color is clear, and it's clean. Level was rather low. It does not appear to mix with water; stays in a little bubble.
Nick
 
DOT 5 is the same as silicone brake fluid. You are "good to go".


"DOT 5 brake fluid is silicone, meaning it doesn't absorb water. It's not compatible with the other brake fluids and is used mostly in classic cars that remain in storage for long periods and need a brake fluid that doesn't absorb water."
 
Hello Nick; I used silicone in an MGB back in the seventies, it worked very well and gave the car a little stiffer pedal, Craig.
 
Craig CT said:
Hello Nick; I used silicone in an MGB back in the seventies, it worked very well and gave the car a little stiffer pedal, Craig.
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I would be hesitant to attribute a stiffer pedal to one or another fluid. All things being equal, I don’t believe either liquid would be capable of that result.
 
Get a cup of water . Then remove some brake fluid from the master cylinder. Pour it into the water. If it beads up it’s silicone, if it turns the water cloudy it’s dot 3.
 
ford38v8 said:
I would be hesitant to attribute a stiffer pedal to one or another fluid. All things being equal, I don’t believe either liquid would be capable of that result.
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Hello Alan; It did have a stiffer pedal but it could be the old fluid had some air or moisture in it, Craig.
 
My take on DOT-5 fluid is this. It works well and last a long time, but it is difficult to bleed. I had it in a '68 Corvette that I installed all new brakes in. It was very difficult to get bled. It almost caused my girlfriend to move out after she helped me bleed the system. Once I got it in, it was great. However, I'll never use it again for two reasons. First is the difficulty getting it installed properly. Secondly, it is incompatible with ABS systems and is no longer in general use. I am afraid that, down the line, it may become difficult to obtain and very expensive. Also, I don't think the altitude where I operated the car varied by 500 feet. I have heard that it does not take well to large altitude changes. I now use DOT-4 and test my systems periodically for moisture content. I have found that it takes 10-20 years for it to get to the point where the moisture content becomes worrisome. At that time, "Speed-Bleeders" have made flushing the system a mundane maintenance procedure.
 
Still a bit confused: Mine appears to be clear(ish), but won't mix with water. I see images of purple DOT 5 and Yellowish DOT 5??
Nick
 
Nick Bernier said:
Still a bit confused: Mine appears to be clear(ish), but won't mix with water. I see images of purple DOT 5 and Yellowish DOT 5??
Nick
Click to expand...
After Dot 5 is installed and in use for a length of time all trace of purple color
will disappear and it will tend towards yellow or clear, just as mine has.
 
I installed DOT 5 in my car years ago. It came out of the bottle purple-ish, but turned clear in a couple years. Others in the area had the same experience. I would not use color as an indicator of DOT 5.
Performing the test described by Ken/Alabama is the way to know.
 
Picked up some DOT 5. It's definitely purple!!
Thanks for all the help,
Nick
 

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38 coupe said:
... I would not use color as an indicator of DOT 5.
Click to expand...

Yes, you can't always rely on color to determine brake fluid type.

The FMVSS requires non-silicone based brake fluids (DOT 3, DOT 4, DOT 5.1) to be either clear or amber colored, and silicone based brake fluids (DOT 5) to be purple.

Older stock of brake fluids may have differing colors, however.

I used to alternate between a blue-dyed and amber-dyed DOT4 brake fluid to aid flushing. The two were identical other than the dye color. The blue version is no longer sold in the US.

If your car has had fluid in it for a long time, it may have a clear DOT 5
 
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