brake line corrosion questions

Internal brake line corrosion is caused when the hygroscopic brake fluid takes up water from the atmosphere or from contamination.

Heat can cause the fluid to darken, so that alone is not a perfect indicator of contamination.

On my Reatta, I have to change out the fluid every two years or face losing a Teves master cylinder. A Teves cylinder can cost near $2000 to replace, so you can see the importance of insuring that it is well taken care of.

I think this is a fair time to change out your Toyota fluid as well. If you can do it yourself, it will only cost a few bucks.

============ Here are two additional ideas:

used the second, not the first.And a third idea from Bob Hoover, that I haven't tried but soundsgood, Get a length of rubber hose to fit tightly over the bleeder screw, and close the opposite end by plugging it with something like an appropriately sized sheet metal screw. Then get a very sharp knife like a razor Exacto knife and cut a clean slice near the end of the hose about one inch long. Now get a bottle, fill with enough brake fluid to cover the end of the rubber hose connected to the bleeder screw. Now when you step on the brake pedal with the bleeder screw open the fluid will force its way past the sliced hose which will subsequently close on itself to seal. The weakness in this system seems to be potential air leakage past the bleeder screw threads, but Bob is a very sharp guy and it seems to work for him.

The color of the fluid is not as good an indicator. You have to use test strips:

Check out the picture for the corroded isolation valve.

But if you change your brake fluid at least every two years you should have no problems. FYI, I change it every year using motiveproducts.com Power Bleeder. Valvoline Syntec or Castrol GT LMA brake fluids are recommended general purpose fluids on these cars. The low moisture activity formulations should absorb less water than the standard DOT3 stuff.

IMO, it's better to get a power bleeder if you work on multiple cars. It'll be cheaper, besides, you'll still have it after you sold the car(s).

snipped-for-privacy@gmail.com wrote:

Brake lines can corrode in two ways. The first is water in the brake fluid, obviously. The second is copper corrosion.

Most brake lines are copper and not steel. What happens is when copper ions seep into the fluid they become a strong oxidizer. The negative copper ions get attracted to iron components and will plate them with a layer of copper. When you see this you'll know copper corrosion is hard at work and that the inhibitors in the brake fluid has long been used up. So don't wait that long. I'd suggest either Valvoline Syntec or Castrol GT LMA.

As far as brake line thickness goes, I don't know how one can check it unless cutting it open. But that won't do it any good. I guess the lines would leak, bulge at the thin spot and such. Checking for deformations and small leaks will the be the first things I guess.

snipped-for-privacy@gmail.com wrote:

Volvo, Audi, Porsche and Aston-Martin use a *copper nickel alloy* for their brake lines, no one uses copper, copper is illegal for brake lines in the U.S. and most other countries. All other manufacturers still use hot dip Terne coated steel brake lines.

Please don't post inaccurate technical data that could result in injury or death.

John, just to speak from the corrosion chemistry side of the question, copper leeching (from an alloy) only occurs at a significant rate if there is water present.

You may be speaking of copper alloys rather than copper, but in any case something else has to be going on before you will see copper going into solution and electroplating onto steel.

In general, water or another strong electrolyte has to be present. (Oxygen or oxidation processes will accelerate this, as will organic acids formed by the oxidation of brake fluid at elevated temperature when oxygen is present.)

I have seen a few cases where copper metal (as from brazing rods) has flashed onto steel, but even that is not corrosive unless a conductive electrolyte is present.

If you have copper plated on steel, you will still not get galvanic corrosion unless the electrolyte is rather conductive, and that usually means water. The galvanic coating of copper gives you the potential for corrosion, but that potential will not be realized in a nonconductive medium.

So if you keep that brake fluid clean and regularly changed out, your likelihood of having problems is quite low.

Good stuff. So I guess that may be why FASCAR thinks copper level instead of moisture level is a better predictor to brake fluid decay. One-year-old brake fluids can have < 3% moisture and yet have enough chemical decomposition that lead to high copper levels (> 55 FASCAR rating) in the fluid?

Sufficient to say that I'd continue to change brake fluids every year. Easy enough with the PowerBleeder. And now I probably won't want anything less than Valvoline Syntec or Castrol GT LMA. :)

Something new everyday.

Ref: according to Brake and Front End Magazine (05/2004), Ricker et al suggested in a NIST report that:

Copper is the first or "Alpha Contaminate" and will corrode before other metals in brake system according to Ricker because "even though copper is in galvanic contact with more active metals, the low conductivity of the brake fluid allows copper corrosion to proceed." You might ask how does copper get in the brake fluid? The answer is from the brake lines. The inside surface of the brake lines is coated with a copper brazing alloy.

"the copper in the brake lines corrodes at a slow rate over several months or years resulting in copper ions in the brake fluid. These ions then act as oxidizers and plate out in the ABS valves when the corrosion inhibitors can no longer prevent corrosion of the ferrous components. According to this hypothesis, copper corrosion starts when the vehicle is new and proceeds at a rate that is limited by the oxidizer content of the brake fluid, mass transport of this oxidizer, and the effectiveness of the corrosion inhibitors in the brake fluid at retarding copper corrosion."

snipped-for-privacy@nospam.nix wrote:

Copper level is very indicative of something being wrong. Copper is below hydrogen on the electromotive series, which should mean that is it not attacked by water or protonic acids, nor even the alcoholic hydrogens of brake fluid.

While pure copper may not be attacked, this is not the end of the story. For example, nitric acid is a strong oxidizer and can attack copper readilyu, although the 'acid' part of the molecule is not what is doing the damage. It is the oxidizing nitrate portion.

Once a copper oxide or other salt is formed, THEN those salts may be dissolved in other solvents rather easily, and they can set up the galvanic cells that cause severe corrosion when an electrolyte is present.

The chemistry doesnt always fit obvious theory, as you can see.

But you are very right that copper electrodeposition can cause big problems, and one of the best ways to stop this is to keep the brake fluid clean, fresh, and dry.

Keeping copper alloys out of the system is not a bad idea either, when possible.

Best regards

Wheew. Thanks for the high level of details. Now the concerns of the likes of FASCAR, Brake and Front Ends, etc. make a lot more sense. Haven't thought about it in these more complex aspects.

But as you said to mitigate it is amazingly simple: change brake fluids regularly!

snipped-for-privacy@nospam.nix wrote: