Can brake fluid break down ?

'Break down' is perhaps not the best description, but the most meaningful answer I can give is 'yes'.

Brake fluid can absorb moisture, oxidize, and become contaminated with corrosion byproducts. It is theoretically possible for polyethers, such as most brake fluid compounds, to form ether peroxides. I have never seen this happen, and doubt that it is a serious problem, but possible nontheless. (Ether peroxides are explosive compounds)

Brake fluids degrade, and in my opinion it is good practice to flush the brake system every few years.

I don't think it generally really breaks down as much as it absorbs moisture over time, which lowers its boiling point. It tends to get darker in color when it's absorbed some water.

That is a 'really' loaded question.

Search google.com in groups under this group and you will see more pros and cons than you likely have time to read.

Some makers say no, some say yes.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Denny B wrote:

I have heard that if the brake fluid absorbs enough moisture, then it can cause brake failure under harsh condidions (emergency braking). The theory is that as the fluid is compressed, its temperature rises. A sudden rise in temperature could cause the water to vaporize. As soon as the water vaporizes, then this has the same effect as having an air bubble in your brake line - the brakes fail because the air compresses at a much faster rate than the brake fluid. (the brake pedal falls to the floor as you fill your pants ;)

The local Automobile club claims to have a device to test for the presense of moisture in the brake fluid. They recommend that it be changed/flushed every two years.

Is the theory true? Not sure. However, given that the cost of flushing the fluid is relatively cheap, and the consquences of brake failure could be quite severe, why take the chance?

I have driven primarily GM cars, and a couple of Chryslers. In each case, the brake lines have been flushed as a result of brake caliper or brake wheel cylnder replacements. That has amounted to approximately every 5 years. So I can say that the fluids have been replaced every 5 years, and I have never had a problem.

YMMV

Brake fluid is not compressible to any significant degree. If it were, the whole notion of a hydraulic brake system would be out the window.

The fluid boils because when you brake, you're converting your vehicle's kinetic energy into heat, some of which is transfered through the brake caliper into the fluid. (You can test this by touching your brake rotors after some hard braking. I suggest using a hand that you don't like very much, like someone else's.)

As part of our preventive maintenance program for fleet vehicles, we flush the brake fluid every two years or

50K, WOF. If you would see the crap that comes out when the bleeders are first opened you would do the same. ;)

mike hunt

cloaked wrote:

snipped-for-privacy@NOSPAM.yahoo.ca (cloaked) wrote in news:3f485f7a.23137690 @news.fu-berlin.de:

Having air or steam in the system would most likely not cause the petal to go to the floor, but it would feel very spongy. You would still be able to stop, but the stopping distances would probably increase substantially.

You have never had air in your brakes have you?

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Preventive Maintenance is a GOOD thing. Especially when it is as cheap as this job would be. Likely way cheaper than the increase in your insurance premiums???

:)

Approximately 8/24/03 00:01, Matthew Hunt uttered for posterity:

Brake fluid with water in it also isn't compressible.

Brake fluid does not boil unless something is wrong with it. Unlike a liquid, brake fluid vapor compresses very nicely and makes a really really bad brake actuating substance.

If your brake fluid is boiling, it has too much water in it or you are using the wrong grade of brake fluid. Even with brake rotors bright red, there should be no boiling.

Didn't know AAA recommended the two year change interval that several european car manufacturers do. IMNHO, it is a good idea for *my* cars, and is always one of the first things I change when buying a used car. Possibly overkill, but it is *my* car and I have this odd preference for brakes working perfectly when I use them.

Approximately 8/24/03 05:49, snipped-for-privacy@mailcity.com uttered for posterity:

Wonder if folks who leave their brake fluid in for 10 years are the same ones who buy lottery tickets as their retirement income strategy.

Unfortunately, Lon, not true.

I have boiled fresh new brake fluid, driving in the Rockies and pulling a camper. Frigging discs were glowing red hot, and brake fluid fumes came out like a forest fire.

I was damn lucky to survive this one.

Let it cool for a couple of hours, topped up and bled, and went on.

Approximately 8/24/03 18:50, Larry Smith uttered for posterity:

What, that if you boil the fluid, it has too much water or you are using the wrong grade? Don't see anything false about that.

I see no problem with adding that "or you are driving the wrong rig and brake system for your load...or are driving it too fast and in too high a gear" as another cause.

Surprised you didn't smell the pads cooking before you were able to glow the rotors....unless you were using an aftermarket pad that overheated the rotors. I've smoked many pads, but the only time I've ever red-heated rotors was racing. However am a coward and tend to take it pretty slow in the mountains having grown up in them and lost it a couple times coming down the wrong grade.

SAE tests (random sample of one, three, and 6 year old vehicles - see article in sho times) showed that the average moisture level in brake fluid of 1 yera old cars exceeds 2%, and that 25% of all the cars sampled had a better than 8% moisture content in the fluid. Dot 3 (Ford Heavy Duty DOT 3 to be specific) brake fluid boils at 290 degrees F with

4% moisture (saturation point for DOT testing - any more and you're on your own - Technical data courtesy of Leica Refractometers. and about 260 degrees F with 6% moisture. I think that you can get your brakes past 260 degrees no problem, I know I can, and if you drive in the city you will too. Once you have more than 4% water content in your fluid, you will start to get little pockets of water in your fluid, if one of those is in your caliper, it will boil, and presto, no brakes. Glowing red temperature is in the 900 (barely visible) - 1000 degree range (I is a physicist - so I best know some of these things), and if your calipers are in contact through the pads, they will reach these temperatures. Good luck in not getting your brakes to cook going down the mountains, mine might, and I run good (read - much better than stock) aftermarket brakes.

Andrew

L>Approximately 8/24/03 00:01, Matthew Hunt uttered for posterity:

Anthony - if you get a bubble in your line that's big enough (either due to air or boiling water), your pedal goes direct to the floor - absolutely NO brakes - great feeling heading into turn 3 at 85mph - been there, sat in a cloud of dust and was glad nothing worse happened - last speed of that day for this cowboy. Good laughs over a beer that night though.

Andrew

Anth> snipped-for-privacy@NOSPAM.yahoo.ca (cloaked) wrote in news:3f485f7a.23137690

Andrew Paule wrote in news:LBf2b.1349$mj6.37174 @news.uswest.net:

news:3f485f7a.23137690

Hrm...I've had small amounts of air in my brakes before from boiling them, petal never went completely to the floor, almost, but not completely, unless it had quite a bit of air (master cylinder dry). Was spongy as all hell, but a couple of pumps and it did stop abiet in a much, much longer time frame. Of course...this was on the old courier, which would actually self-bleed if you opened up the bleeder valves. The lines were routed very well. It is possible that some of the air may have actually escaped back through the master cylinder as I pumped them up.