Does brake fluid have a shelf life?

Brake fluid is hygroscopic (it absorbs water). I'd have thought even a good screw stop would have let in significant amounts of moisture from the air over the course of 15 years, rendering the brake fluid compressible and therefore no use for applying sufficient braking force to the brakes when the pedal was pressed.

Scrap it. Brake fluid sucks up moisture out of the air like the government sucks up money. Not worth the chance of contaminating the system.

"Steve W." wrote in news:gi42pb$boc$1 @news.motzarella.org:

Castrol and Girling fluids used to come in round metal cans with screw-off caps. Even a metal cap has a polymer or coated-paper cap seal, and that's the part that is not gas-tight. After 15 years that seal will have admitted a lot of water molecules.

Especially considering how cheap brand-new fluid is...

If it is a metal can and has an airtight seal, it is probably OK. However if the seal has been compromised in any way it is likely full of moisture and only good for paint stripper. Personally I would not use it. If it has ever been opened and partially used, it is definitely trash. DOT 3/4 brake fluid is highly hygroscopic, this is why you should change it every couple of years.

nate

Oh hell, I never touched the brake fluid on my '88 Celebrity in the 14 years it was in there. Never had any indication it was affected. Same with my current cars, one a '90 and the other a '97. Never touched the fluid. These are closed systems.

--Vic

Don't they have a reservoir vessel under the hood with a removable screw top where you can check and top up the level as required? I bet that top is not

100% airtight and will let a small amount of moisture in over the months and years. Isn't replacement of the brake fluid something that is done at service every few years?

I imagine the same is true of the power-steering fluid (if the car has PAS), though the effect of water in the fluid is much less severe than for brakes.

On Mon, 15 Dec 2008 13:02:00 -0000, "Mortimer" wrote:

I'm sure some will argue the seal, whether the lid is screwed on or clamped on, isn't 100% effective. Evil moisture laden air will somehow infiltrate. I don't buy it. But I won't argue against changing whatever fluid you want to. It could be a safety issue. Just remember that pouring it in the reservoir will expose it to the evil moisture laden air to a much greater degree than any seal leakage. Same with even checking it. Hell, when you pull the cap it starts sucking up water. All I'll say for sure is I've had many cars for many years and NEVER changed PS or brake fluid and NEVER had brake problems related to fluid. Maybe I'm just a lucky guy. I will say the way I drive I can count the times I have had to stand on my brakes in the last 30 years on less than 10 fingers. They worked fine, with no excessive fade. Maybe if had more emergency stops it would show up. I'd like to see a real chemical analysis of old fluid in a normally sealed master cylinder before I change my habits. Problem is in the process. Going by what you hear from the moisturephobes, just opening the lid will have it sucking up water from the air, nullifying any lab results. The reservoir seals I see on the GM cars I've had don't look like they'll let any air in, and that's been good enough for me. If anybody thought critically about this, they'd just put some air pressure on a removed cylinder and see if there's leakage through the cap. I'll bet they're good for a couple PSI, more than they'll ever get from the outside.

--Vic

--Vic

If it hasn't been opened and the seal is completely tight then it may be ok. Considering how inexpensive a can is, I would just buy new and not have to worry about contamination.

Clearly, you have never owned a Teves braking system... (And maybe that confirms that you are a lucky guy)

NO your brakes are NOT a closed system. The newer units are better at keeping air out than they used to be but they still let air in. Is the brake fluid in your vehicles still crystal clear? That is the color of good fluid with no moisture. ANY other color is moisture and rust. Care to guess what effect that rust has on the rubber seals and pistons in the system, how about what it does to the passages in an ABS system.

And YES Brake fluid is listed as a service item in many vehicles owners manuals and service books.

Depends on the manufacturer. German manufacturers typically recommend replacement every 2-3 years. American manufacturers do not. The story I was told was that changing brake fluid had a small but non- zero chance of contaminating the ABS HCU with chunks of rubber from seals, hose linings, etc. and that since they figured that most cars weren't in service for much more than 10 years the car itself would be retired before moisture contamination of the brake fluid would become an issue. If, however, you want to keep the car *longer* than 10 years... I'd recommend replacing it.

AFAIK power steering fluid is just a modified oil like ATF (actually ATF is used in many power steering systems) so this is less of a concern.

nate

AFAIK power steering fluid is just a modified oil like ATF (actually ATF is used in many power steering systems) so this is less of a concern.

====

I've always wondered why brake fluid isn't just a non-compressible oil: there must be something very beneficial about the qualities of brake fluid to put up with the disadvantage that it is hygroscopic.

Yep, the hygroscopic ability is actually a benefit. Why? Because the moisture that does get into the system is held in suspension in the fluid. That keeps it from settling in one spot and freezing or boiling. It also means that you don't get a localized spot of rust. It also doesn't boil at braking temperature and doesn't expand or contract very much in regard to temperatures.

Fine, do the service. I don't know what color my brake fluid is. I NEVER look at it. Well, maybe every 5 years or so, just for the hell of it because I'm out of beer. By then I can't see colors anyway. Doesn't matter anyway. Just like engine oil gets colored right after a change, so does brake fluid as it immediately picks up color from rubber lines/seals. Doesn't mean anything. I don't even take the MC cap off when I squeeze calipers. Now, how about clueing me in about how air/moisture gets in the system. Not a horseshit system with leaks, but a perfectly functioning system. I've done maybe 50 brake jobs and never messed with brake fluid unless I broke a line to replace a cylinder. And even then I just add what I need to bleed. Only way changing brake fluid would be a concern to me is if I was always excessively heating my brakes. I don't. But like I said, I don't tell anybody else not to do it. They can change the air in their tires while they're at it. Again, all my cars are common GM's. If somebody tells me Fords or Hondas or whatever are different, I'll listen.

--Vic

It gets into the system in a few ways. One is that the fluid gets exposed to air when it is installed. Also every time you use the brakes you allow air into the system. Why? They ALL leak some. The seals shift every time you apply the brakes and allow air past them. Same thing with rear wheel cylinders. You step on the brakes and let off, the fluid retracts and it draws some air past the piston seals. The master cylinder pistons have air behind them as well so when those seals move as well the air can get past them. Go pull apart the brakes on one of your "perfectly functioning" vehicles. You will find rust in the wheel cylinders and calipers. Guaranteed. They ALL let air in at times.

You can choose to believe it or not. Especially since it sounds like you don't do any maintainance on your vehicles anyway.

"I don't know what color my brake fluid is. I NEVER look at it. Well, maybe every 5 years or so, just for the hell of it because I'm out of beer. By then I can't see colors anyway."

Guess you don't bother to check the oil or coolant either. I have done closer to 500-1000 brake jobs so far and see what rust and crud do to the system. Talk to any shop mechanic who does brakes.

If your car has an ABS system it is even more critical that the fluid be changed regularly.

.

Some people agree; some people disagree. Hence the recommendation for DOT 5 (silicone) fluid for classic cars. Me, I prefer to stick with

3/4 and change it every couple years. silicone is not hygroscopic but can cause pooling as Steve says, and is slightly more compressible than 3/4. Also the two are not intermiscible so on the road repairs are far easier if you use DOT 3/4 although many FLAPS are now stocking DOT 5 so this is less of an issue than it used to be.

Thread drift: used to be, companies specializing in rebuilding obsolete brake components used to sleeve the cylinders in stainless steel. Lately I have seen a shift to brass. Anyone know why this is? I honestly don't know what the advantages/disadvantages to the two materials may be, although obviously either one should last longer than cast iron as the usual failure mode seems to be corrosion.

thanks,

Nate

I believe what I see. And I haven't a single brake fluid related problem with brakes on any of my cars, or the cars I maintain. Some have gone 15 years without touching the original stuff put in the factory.

As a matter of fact I hardly ever do that anymore. The cars I'm running now went like this. A '90 Corsica 2.2 I replaced the hoses/coolant/thermostat and popped the GM tablets in because I saw a rust stain on the head.

10 years ago when I bought it. The rad cap hasn't been twisted since. Why would I look? It doesn't freeze and it doesn't overheat. If I was going to keep it a few more years I might change hoses/coolant again. But I ain't. First serious problem it gets retired. Pretty much the same with the '97 Lumina. Did the hoses/coolant/thermo 5 years ago when I bought it. Since the girls took it to Florida last year I put new hoses/coolant/thermo on it again, and threw in a water pump too. I change oil 2500-3000. Once I confirmed they aren't burning it I quit checking. I'll hear the lifters or see a leak if anything changes. It's pretty relaxing having cars that don't burn oil, leak oil, or have bad brakes, especially when I buy them for peanuts. I'll let the guys who spend the bucks get all anal about it.

No thanks. I been just fine not examining cylinder bores for pitting that doesn't affect me. Hey, I'm not arguing with you, and I respect your opinion. Different strokes. Might need your troubleshooting advice again.

--Vic

Brass is a lot less expensive to work because it's so much softer. And if you use shitty Chinese cartridge brass, the material can cost less too.

--scott