brake fluid ID

[william e snyder]

i need to add a little fluid to my non pwr brk 66 master. is there a way to determine if the fluid is silicone or not, and does it matter? the car has stainless calipers and that is why i suspect the silicone.

[Joe L.]

Re: brake fluid ID

william-----

It's very easy to positively ID. Take a small, clear glass jar and siphon into it some of the fluid currently in the master cylinder. Then, add some DOT 3 or 4 glycol based fluid to the jar. Shake the jar and let it sit for several minutes, at least. If you see a "phase separation" (i.e. 2 distinct fluid "layers") in the jar, then the fluid in the master cylinder is DOT 5 silicone. If the fluids mix completely and there is no "phase separation", then the fluid in the master cylinder is either DOT 3 or DOT 4 glycol-based fluid.

An additional test that you could run is to take a small amount of the fluid out of the master cylinder and place it on a painted surface (a TEST surface and one that you don't care about). If, after a few minutes, the fluid mars or lifts the paint, then you know it's DOT 3 or 4 glycol fluid. If it doesn't affect the paint, at all, then it's DOT 5 silicone fluid.

Keep in mind that DOT 5 silicone fluid is dyed purple. However, the dye rather quickly changes color to yellow. Since regular DOT 3 or 4 fluid is USUALLY an amber-colored liquid, it's very hard to distinguish between them after the purple color changes. However, the DOT 5, even after it changes color to yellow, is still a much more pronounced yellow than the normal color of DOT 3 or 4.

[Duke W.]

Re: brake fluid ID

You can also use water. DOT 3 or 4 glycol based brake fluid is miscible with water. DOT 5 silicone is not.

DOT 3 and 4 has a distinctive odor. I don't recall that DOT 5 has much detectable odor.

Duke

[Kent K.]

And Bill, ya don't want to mix em

Cause if you do, your rubber components and seals within the MC will probably fail the next time you brake. That happened to me after the shop rebuilt my '54 Chevy Belaire system with silicone and I topped the MC up with DOT3 or 4. Brakes worked fine going to work ... comming home, no brakes but the parking brake stood the test. Wheeeeeewwwwwww
Kent #6201

[Frank C.]

Re: And Bill, ya don't want to mix em

The DOT 5 fluid I've been using (GE) is purple in color and very obvious.

[Terry M.]

The color of DOT5

My STP DOT5 was purple to start with, but that lasted only a couple of years.

[Frank C.]

Re: The color of DOT5

Terry....mine is still purple after 15 yrs

[Bill S.]

thank you

thanks for all the great info. this is why i joined and follow the bord,bill