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THE SWIRLING MYSTERIES OF BRAKE FLUID

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We have spoken on this topic in the past, and I continue to get inquiries on it, and see problems, many serious, caused by it come through the shop every day, so it deserves an updated discussion.

My information comes from a 34-year association with NAPA as their salesman, and 40 years of working on British. As a salesman, I had inside access to the manufacturers` research, development and the Department of Transportation regulations they had to abide by.

Brake fluid; simple and unassuming as it seems, generates a lot of confusion and controversy! What type, what brand, what temperature, what color, what about our British seals compared to American? What are the side effects of neglect? What can/should I do to maximize my safety?

Let’s start with some real basics.

In the U.S., brake fluid has to meet the Department of Transportation standards for wet and dry boiling temperature, corrosion resistance, and moisture absorbsion, hence the common terms: DOT3, DOT4, DOT5, DOT 5.1, ect. Without getting clinically detailed, the basic idea is, the higher the DOT number, the higher the boiling temp is, and the more resistant to water absorbsion the product is.

U,S. cars and trucks have used DOT 3 for many, many years. Then higher speed and brake temperatures required an upgrade to DOT4, and then came ABS brake systems, and we needed an improvement to even higher temperature and lower moisture spec’s. They gave it the classification of 5.1. All of these are Glycol based fluids, and for less confusion, they should have labeled it 4.1, so we wouldn’t confuse it with Silicone.

Somewhere in-between, DOT 5 came in, which is Silicone based, and early on was mainly touted as a performance option. And that’s when the debate started. As the debate grew in intensity, and people began to take die-hard stands on their choice, naturally, information became tweaked and mis-interpreted, more on this in a minute.

So, to begin our discussion, since all brake fluid is rigidly tested and has to earn its classification, we can feel safe and go by the DOT number that is required on every label. (Ok, Ok, if you have a favorite brand name, you can call it the best in its class).

What is required of brake fluid? It must be stable at high and low temps, resist boiling at the high temps of the braking action, prevent corrosion, resist water contamination, be non-compressible, lubricate the sealing cups, flow easily at high and low temps, and be compatible with all other brake fluids in it’s class, and compatible with all compounds found in a brake system. Tall order, eh?

I see three areas of extreme concern to all of us driving British cars:

1) Making sure the brake fluid does not fail from boiling, in high heat emergency stops.

2) Preventing corrosion and subsequent brake failure.

3) And the question: “ Should I use regular or silicone brake fluid?”

Let’s take on the first two, since they are tied so close together, fluid failure from boiling and corrosion. By it’s nature, Glycol brake fluid is hygroscopic, meaning it attracts and absorbs moisture, from where? The air around us has a varying amount in it, more in Seattle, less in Wenatchee. How does it get in? Every time we open the lid to the reservoir, also through the vent hole in the cap, and passing by the rubber cups and seals, and through the wall of the rubber hoses in the system. (Yes, small amounts over a” long “ time). This water dilutes the fluid, lowering the boiling point first, then proceeds to chemically create corrosion and sludge, ruining the smooth sealing surface of all the brake parts. And it does this far faster than we previously imagined. YIKES!

NIST, National Institute for Standards, tests have shown, that in it’s first year, brake fluid can absorb enough moisture to reduce the boiling point by almost half, and by the third year, is dangerously low for a panic stop in hot conditions, and is starting to build corrosion.

Should I use Silicone fluid instead? Here are the real benefits, as shown by NIST tests: more stable in all conditions, resists physical and chemical changes, non toxic and non corrosive, (safe on your paint), lowest viscosity change in temperatures, does not absorb water, has the highest dry boiling point.

So what’s the problem?! Sounds like a slam-dunk, doesn’t it!

Here are the actual weak points of Silicone fluid, by NIST tests: absorbs air (oxygen, hard to bleed, requires special procedures and handling, softer pedal feel), still allows moisture to enter and pool at the lowest point instead of being absorbed and dispersed throughout the fluid as in glycol fluids, (dangerous pools of water in the low points, like calipers or cylinders and will boil at much lower temps than contaminated glycol would), repels glycol and any contaminants, forcing them to gather and form “clots” in the system.

Something brand new I’ve noticed, the new master, slave, wheel cylinders I am getting have a bold warning on them, “ USE OF SILICONE FLUIDS VOIDS WARRANTY”. I don’t know what they think the problem is or how strict they will be about it yet.

Conclusions for Silicone fluid: It is an outstanding product that must have a “new” system to start out in, with no trace of previous fluids, and new seals in the master, wheel and caliper cylinders, and new hoses. Then, every 6 months, should be bled, (not flushed) to expel the moisture gathering at the low spots, then tested for corrosion contamination and flushed as indicated. These steps will allow you to reap all the benefits of this fluid.

Conclusions for Glycol fluid: If your system is untouched and over 5 years old, prepare for brake system work. Whatever fluid you are using now, stay with it until you have major work done and can start clean. In digging around, I found the original recommendations for our cars, “ fluid changes every 18 months, and examination and replacement of rubber parts every 3 years”. Even in the 1950`s they recognized the problem! Once the system is safe, flushed and clean you can then switch to the highest dry boiling point fluid you can, and a preventive maintenance of bleeding every six months to a year and flushing every two to three years is minimum. Accurate testing of the fluid for moisture content and corrosive level is available at your favorite shop, like British Car Ranch.

Let’s de-bunk some old myths`, like “Only use Castrol Green, or Crimson”, These are old inferior chemistry, and not made any more, Castrol has far superior replacements for them now.

“American fluid will ruin our British seals”. They haven’t made natural rubber seals in 50 years, and, all DOT fluids have to work with all seal chemistries`, even the not available natural rubber! I believe the problems we hear about seal swelling and failure are related to the brake fluid having degraded and changed to a caustic solution from water and corrosion, not from clean healthy brake fluid.

“I’m safe from moisture and corrosion with Silicone!” As we saw, Silicone won’t absorb, but will pass moisture and still needs to be bled out to prevent corrosion and lower boiling points, and should NEVER be mixed with old Glycol fluid.

I intend this to be a quick read overview piece to get you thinking about your car’s safety, purposely omitting a ton of detailed info. For those that want more details, or have a question on your car, or even if you have a spirited debate over my information/conclusions, please contact me at britishcarranch@.

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Steve & Christopher Day

British Car Ranch

Wenatchee WA.

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