Brake fluid -how to tell which kind you have DOT 3 or DOT 5

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Looks like complete separation to me. That would indicate dot 5 to me.

If you have some dot 3 at home, mix some water in it and look at what that looks like. You should see a difference.


Portland, OR
I'm concerned about making a mistake here. Anyone know where I can send out a sample of it to determine what it is ?
The master looked newer so the system has been worked on.
Looks like i lucked out!! thought I accidentally added the WRONG fluid! going by the "test" methods listed in the forums, looks like i in fact had DOT5 silicon fluid (Bright yellow) the new purple fluid I added mixed well with the yellow.

The dot 3/4 fluid was MUCH lighter almost clear it mixed with the water and "absorbed" it.
when water combined with the DOT5 it seperated like oil/ water .. as seen in the picture.
Just though i would add another visual aid to the mix ! hehdot 345.jpg


New member
terryville, ct
Reviving an old thread, but hoping someone can help me and perhaps someone else..

What should be done if Dot3/dot5 brake fluid was already mixed, or dont know if it was mixed. Hoping someone can help with the repairs.

Will a flush be sufficient? With what?
How would one flush to make sure the entire system is the same fluid?
Which fluid should be added back in? or would it matter after a flush?

I just bought a '77 M880 that I am going through for registration. Really the only thing in need to do to get it registered is the brakes.

The prior owner said the brakes were always 'soft' and that he had added brake fluid over the years, but they had never found any leaks.
After driving it the brief distance to my house the description of "SOFT" would being an understatement!! While they do work, they are VERY Spongy and need to have constant pumping to work. You even have to pump the brakes to KEEP the truck stopped when in gear.

Not knowing this information, I was originally going to bleed the brakes with DOT 3 (so at least some of Dot3 was added but could still be removed).. However the first bleeder valve i hit is stripped and frozen, so i was just going to replace the wheel cylinders..

Now that we are up to speed, where should i go from here.

I was hoping to get it on the street after a simple brake flush, but quickly realized that wasnt going to happen..
I hope you are not going to tell me I am going to have a complete system disassembly and rebuild.. :/ that would be no bueno..

Thanks in advance..
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