Green Brake Fluid - PeachParts Mercedes-Benz Forum

MBDad777 · #1 11-10-2003, 10:14 PM

When I changed the brake fluid yesterday I found the system full of green fluid. It looked just like antifreeze. What the???

Also, I used a pressure bleeder at 30psi. The flow at the front calipers was real good. But I only got a trickle out of the back ones. Why?

G-Benz · #2 11-11-2003, 10:22 AM

I'm guessing you are refering to your 99?

The green brake fluid is a silicone based fluid (DOT5 I believe). It's designed to repel moisture. DOT4 is amber (or cranberry-colored when really dirty), and probably what you are used to seeing.

The two fluid types are not to be mixed together...use what is specified on the reservoir or in the owner's manual.

As far as not getting as much flow out of the rears, I can't say for sure...sorry.

MBDad777 · #3 11-11-2003, 01:39 PM

Yep, I'm talking about the '99 C280. I've heard of the green DOT5 stuff but I find it very unlikely that's what it was for two reasons: the previous owner treated the car like a pile of crap and the interim dealer who bought it from the auction and prepped it before selling it to me didn't have a clue how to service a Mercedes (they put green 'regular' antifreeze in the cooling system, for example). But anything's possible, I suppose....

Kestas · #4 11-11-2003, 04:26 PM

Try mixing the brake fluid in water. If it mixes, it's glycol (DOT 3, 4, 5.1). If it doesn't mix, it's silicone (DOT 5).

haasman · #5 11-11-2003, 05:13 PM

Kestas,

I am sure you are suggesting taking some brake fluid OUT of the system and then mixing it with water?

G-Benz · #6 11-11-2003, 05:16 PM

Quote:

Originally posted by haasman
Kestas,

I am sure you are suggesting taking some brake fluid OUT of the system and then mixing it with water?

Obviously so...you DON'T want to add water in the system!!!

But your brake system probably needs to be flushed out anyway...especially if you aren't sure what's even flowing through those brake lines!

Gilly · #7 11-11-2003, 07:35 PM

Not to worry about the DOT5. I've seen the MB Dot4+ turn a greenish tinge also, just like you say, when it's been ignored a few extra years than it should have. No real positive idea why, my guess is something in the system that is bronze, brass, or copper doing a little corroding, just enough to tinge the fluid greenish. Never had a problem with these as far as doing a fluid flush, seemed fine afterwards.

Gilly

manny · #8 04-21-2005, 08:49 PM

None of them look fit for human consumption.
Well.............maybe as a laxative.

Duke2.6 · #9 04-21-2005, 08:53 PM

Glycols are miscible with water so water will mix with DOT 3 and 4 brake fluids. As previously stated, DOT 5 silicone fluid is not miscible with water, and the water miscibility test is good way to positively identify silicone versus glycol brake fluid if you aren't sure what you're dealing with.

The other products are probably all mineral oil based since they don't mix with water and rise to the top. Mineral oil specific gravity is less than water, so petroleum products, even heavy crude oil, will float on water.

Nice work, thanks for the photos!

Duke

Kestas · #10 04-29-2005, 10:36 AM

Algae in diesel fuel (and jet fuel, which is similar to diesel) is a well-known phenomenon. I've never heard of algae in brake fluid. Like Gilly said, it may be copper corrosion products you are seeing in the brake fluid and not algae. The following article supports this thought:

Brake fluid replacement article

All copper corrosion products I am aware of are green in color. Just because one group of people at a shop think it's algae doesn't necessarily mean they know what they're talking about. One guy probably said it's algae, and the rest figured "what else can it be?" and agreed with him. Thus an unproven theory is born and accepted as fact.

Some people are mystified where the copper comes from. If you read the article - and not just skim it - you'll realize that a lot of copper is present in the brake lines in the form of brazing alloy which forms the copper tubing, commonly known as 'bundy' tubing. It is not unlike your paper roll tube which is spiral-wound and glued together. This technology allows for high pressures in relatively inexpensive tubing, and is less prone to manufacturing defects that can lead to catastrophic pressure loss.

The article also mentions that copper is found in spongy or nugget form in the corrosion pits of the ferrous parts. This is interesting, since I found the exact same thing in corrosion pits of aluminum head cooling jacket surfaces on a study I did for an auto manufacturer.

I could easily verify the presence of copper in the fluid in my lab if you could dry a tiny sample of the green fluid and send it to me.

Duke2.6 · #11 04-29-2005, 11:24 AM

Very good article, but the copper issue has me a bit confused. Brake lines are formed from seamless steel tubing and use double flare joints. There are no brazed joints.

Copper tubing is not acceptable for brake lines or any application that sees vibration because it rapidly work hardens rapidly and becomes brittle. Steel brake lines are plated or otherwise provided with a corroison resistance exterior finish, but I don't know what if any coating is generally applied to the inside.

Given that master cylinder and caliper/wheel cylinder bores are typically unplated iron, it probably doesn't matter if the inside of the tubing has a corrosion resistant coating or not. Even without fluid changes, most brake lines are probably more suseptible to external corrosion, particularly in areas that use salt on roads in the winter.

"You might be asking 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 above quote leaves me confused as I don't understand what they mean by a "copper brazing alloy" although the author does describe it as a "coating". For sure brake lines are not copper, but some may have a copper based plating on the inside. Given the problem with copper corrosion, maybe it would be better to leave the inside of the lines bare steel or use a more corrosion resistant coating.

I've used the test strips a couple of times and they said my fluid was okay, but I've had the habit of doing bienniel flushes for nearly 25 years and will continue to do so. In that time I have never had to overhaul a hydraulic component on any or my cars which range in age for 16 to 42 years.

Duke

Kestas · #12 04-29-2005, 01:16 PM

Brake lines are not formed from traditional seamless tubing but are formed in a unique way. A thin strip of steel is spiral wound in a tight diameter (hence, the earlier reference to paper roll tube) and the thin gaps are filled with an copper-rich alloy identical in composition to a brazing alloy.

The outside of the tube is then coated with terne plate, which is a lead-rich coating used for corrosion resistance. The inside is not coated. The braze material is naturally open to the brake fluid inside the brake line.

I imagine that, over time, water gets absorbed into the brake fluid and an electrolytic cell develops, moving the copper ions around from the brake lines to other parts of the system that may be highly electrolytic, such as the corrosion pits in steel, where the copper drops out of solution.

Given all the other good stuff on the internet, it's interesting that there's nothing written on bundy tubing, nor can I find any reference in my steel or automotive handbooks.

Kestas · #13 04-29-2005, 02:00 PM

Unless you examine a new brake line very closely - almost with a magnifying glass - you won't see anything other than steel.

To prepare the sample, anything that works will do. You can try drying it on aluminum foil. A little heat may help it along. If that doesn't work, try drying it on a paper towel (not office paper). Whatever method you use, do the same thing with new brake fluid to use as a control sample.

I need only very little sample. Everything should fit in a 37 cent envelope. If you're curious, I'll be using SEM/EDS methods.

Once the samples are prepared, PM me and I'll give you an address. This'll hopefully put this issue at rest.

Wes Bender · #14 04-29-2005, 02:36 PM

This thread is a perfect example of why we should all be changing our brake fluids annually. Been doing it for years on all my vehicles and I don't have brake problems with any of them. (Now where's that piece of wood I need to be knocking on...)

Duke2.6 · #15 04-29-2005, 07:37 PM

Quote:

Originally Posted by Kestas

Brake lines are not formed from traditional seamless tubing but are formed in a unique way. A thin strip of steel is spiral wound in a tight diameter (hence, the earlier reference to paper roll tube) and the thin gaps are filled with an copper-rich alloy identical in composition to a brazing alloy.

The outside of the tube is then coated with terne plate, which is a lead-rich coating used for corrosion resistance. The inside is not coated. The braze material is naturally open to the brake fluid inside the brake line.

I imagine that, over time, water gets absorbed into the brake fluid and an electrolytic cell develops, moving the copper ions around from the brake lines to other parts of the system that may be highly electrolytic, such as the corrosion pits in steel, where the copper drops out of solution.

Given all the other good stuff on the internet, it's interesting that there's nothing written on bundy tubing, nor can I find any reference in my steel or automotive handbooks.

Well, this is new information to me. The only example I have around is the original front to rear brake line from my 63 Corvette, which appears to be seemless steel tubing with a zinc or cad plate. I recall fabricating a new line from what appeared to be essentially the same material that was sold as "brake tubing".

I'm not familiar with this tubing construction technique. Is it unique to some manufacturers? Why is this type of construction used? I take it the name of this type of tubing is "Bundy tubing"?

The brake lines on my 190 have a dark green finish on them. I assume it's some kind of paint and that the tubing itself is plated.

If copper is a primary source of corrosion in brake systems then maybe this spiral wound copper brazed material should be replaced with something that doesn't have any copper content.

I'm mystified.

Duke

P.S. Did a little googling on "bundy tubing" and "brake tubing". The following pages are interesting.

http://www.copper.org/applications/automotive/brake.html

http://www.cda.org.uk/Megab2/corr_rs/is49/default.htm

It appears that a new brake line material is now being used by some OEMs that is about 90 percent copper and 10 percent nickel, so I suppose that it must not have the work hardening problems of common copper tubing. It's primary advantage is greater external corrosion resisitance than plated steel tubing, but maybe it increases the propensity for internal corrosion because of the copper content. "Bundy tubing" appears to be a rather old construction method, but may be used for some brake tubing applications.

I would not expect the new copper/nickel tubing to be magnetic due to the very low nickel content, however I checked, both the old line from my Corvette and the lines on my 190 and they are both strongly magnetic indicating to me that they are steel.

Duke