Replacing brake fluid

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I shouldn't argue against extra brake safety but experience shows that fluid-induced brake failures are really rare in light duty use and have been for the past 30+ years. Fluid contamination is rare in modern systems as long as it hasn't been opened up for some reason or damaged.

Probably half of all cars and light trucks that are 10 or more years old in the U.S. have never had their brake fluid changed.
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Based on that, wouldn't you expect that brake failures would be a common experience if changing fluid is indeed safety-critical?
 
I had a brake failure a few years ago, in flat central Florida of all places, on New Years Day. The pedal went to the floor. I pulled over and after it cooled off a bit pedal pressure came back.

The fluid was about four years old, and nasty.

Three years later the fluid tested ok with an electric moisture tester, but the MH hadn't been driven in about a year during refit and then covid. About 10 months later the tester indicated that the fluid needed replacing, so I went ahead and did it.

The chassis manual says to replace fluid every three years, so that's what I'm doing.

A friend had a rather exciting experience with moisture in brake fluid in his MH in the north Georgia mountains. He had to sit on the roadside overnight until someone could come out and change the fluid.

Replacing the fluid is really no big deal. One person with a power bleeder can do it in a half-hour. Doing it the old-fashioned way take three people and about an hour.

Usually fluid is replaced with brake replacement, which in cars happens comparatively often; our motorhomes may never have brake pad/shoe replacement in decades. Rubber lines are rather porous to moisture plus of course the master cylinder is opened a couple of times a year to check levels.

It's definitely safety-critical, not very expensive and only takes an hour or two of your time.
 
Thanks for posting this thread, I generally change the brake fluid in our motorhome every 2-3 years (most recently done in March), however this thread reminded me that I have no idea how old the brake fluid is in our 2007 Toyota Yaris TOAD which be bought used almost 3 years ago.
 
DonTom said:
Sounds like a lot of air in the system or a bad master cylinder.

IAC, it probably had nothing to do with the old brake fluid.

-Don- Auburn, CA
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Brake fluid is hydroscopic and the water it attracts boils at a much lower temperature than brake fluid itself. If it turns into steam the brake pressure will compress it instead of reaching the wheel cylinders - have enough steam in the system and the brake pedal sinks to the floor when heavy brake usage heats up the components on the wheels.

You have to change brake fluid more frequently to avoid water contamination in humid environments like Florida than you do in dry climates like the southwest deserts. It's also why you should only use brake fluid from a sealed can, not one that's sat on the shelf for a while after it's been opened.
 
Light duty hydraulic brake failures are rare due to fluid itself like Gary said. As mentioned, DOT 3-4 fluids are hygroscopic. Water is an excellent and very cheap hydraulic fluid--to a point. Besides the dangerously low boiling point that water has as a hydraulic fluid in a system that generates heat, it also makes the polyethylene-glycol based (most common) fluid become acidic/corrosive over time.

And that's really bad for things like the ABS pump hardware, and metal and rubber lines, and seals in the master cylinder and at the wheel cylinders.

10-20 years seems to be the point at which old fluid becomes REALLY nasty and has probably weakened the whole system to some degree. There's still good sense in changing it every few years to keep the system clean and at the correct ph level to get maximum life out of all the hardware.
 
Some years ago (20ish) I was driving home from work and had a sudden brake failure where the pedal went to the floor, and I blew through a stop sign crossing a major high at 25-30 mph, thankfully missing the crossing traffic. I was then able to come to a stop using the hand brake, I was only a fraction of a mile from home at this point so drove the rest of the way using the hand brake. I had almost no warning this was coming, a couple of minutes prior to this complete failure I was stopped at a traffic light and thought this brake pedal feels a bit soft, not much, just enough to register, then less than a mile later as I came to the stop sign, nothing, pedal went right to the floor. The shop I took it to said the seals in the master cylinder had failed.
 
After we moved to CA in the early 1960s my mom took us kids and a couple of our friends to a picnic on Mt. Tamalpais. Our friends had lived in Marin County their entire lives but had never been there. On the 1900 ft. descent to Mill Valley she stopped at the last stop sign, then attempted to stop again and the brake pedal sank to the floor. We weren't going very fast so she was able to put the car in neutral and drift over to the curb. It was a heavy 1956 Oldsmobile 98 and there was no warning of the impending failure, although some brake fade could have been masked by the feather light power brakes on that car. After sitting for about 20 minutes the brakes came back and we drove carefully home. The diagnosis was water in the brake fluid heating up due to the repeated brake applications on the way down - it had never been changed.
 
Definitely old bad fluid, probably overheated by one brake dragging. We replaced calipers, rotors, every rubber brake hose etc. The MC had been replaced a few years earlier and is still fine.
 
Old fluid gets real nasty looking, and with the plastic reservoirs you can see it now, where before you could not with the old iron master cylinders.

Its always been a hassle to find someone to help bleed brakes so finally, last year, I bought a pressure bleeder kit in preparation for new brakes on the RAM. To test out the new Mityvac MV7840 Pressure Brake Bleed Kit for Pressure Bleeding Hydraulic Brake and Clutch Systems, I tried it out on my Pontiac Vibe, just to learn the peculiarities of this pressure bleeder (I have never used one before). The fluid that came out looked pretty good for being 20 years old.

Then I did the RAM so the system would have clean fluid and I would not contaminate the calipers or new hoses when I did the brakes. That too went well, and the old fluid was most likely original (20 yo) and very, very dark and nasty. After doing the brakes I again bled the system and now I have brand new fluid in all the vehicles. (My Ranger got a complete bleed a couple of years ago after the antilock module started leaking and was replaced).

I have always been a believer in fresh brake fluid, it was just too much trouble before I bought the pressure bleeder.

If you have a European car with DOT4, that fluid is even worse about sucking up moisture so you need to heed the flush requirements.

The pressure bleeder has two issues and that is, 1) you use a lot more fluid with it (which has become very expensive), even when I pour the unused fluid back in its original bottle (which I date when I opened it) and 2) cleaning it up is a hassle, as they call for Denatured Alcohol, which is expensive, and I have to run that thru everything to flush the fluid out of hoses and couplings. Lots of wiping and cleaning.

Charles
 
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Gary RV_Wizard said:
I shouldn't argue against extra brake safety but experience shows that fluid-induced brake failures are really rare in light duty use and have been for the past 30+ years. Fluid contamination is rare in modern systems as long as it hasn't been opened up for some reason or damaged.


Based on that, wouldn't you expect that brake failures would be a common experience if changing fluid is indeed safety-critical?
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The hydraulic brake system is not closed or it couldn't absorb moisture.
Why is it All auto mfgrs recommend replacing brake fluid? Moisture in the fluid causes corrosion and when heated turns to steam, which is highly compressible. The result is greatly reduced/no braking ability.
For example, Mercedes recommends replacing brake fluid every two years or 20,000 miles. Ford says every 3-5 years.
The brake cylinder reservoir in my 13 Silverado pickup has air space above the full line = moisture laden air.
In Florida for instance, moisture in brake fluid is much more common than is AZ, NM, or NV. That means hydraulic brakes in FL require more attention.
There are many articles on the web along this line that back-up my post.
Every can of brake fluid I've ever bought says in the instructions to discard unused brake fluid if the container has been unsealed for a specified time period, usually 30 days max.
Afterthought: MH hydraulic brakes are considered heavy-use, as are medium-duty trucks.
 
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Isaac-1 said:
I had almost no warning this was coming, a couple of minutes prior to this complete failure I was stopped at a traffic light and thought this brake pedal feels a bit soft, not much, just enough to register, then less than a mile later as I came to the stop sign, nothing, pedal went right to the floor. The shop I took it to said the seals in the master cylinder had failed.
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Not saying that is impossible but American vehicles built since 1967 have been required to have a dual-brake master cylinder, with separate circuits for the front and back. Both circuits failing at the same time would be really rare.
 
TheBar said:
Not saying that is impossible but American vehicles built since 1967 have been required to have a dual-brake master cylinder, with separate circuits for the front and back. Both circuits failing at the same time would be really rare.
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I had this happen on the 1967 Falcon (first year for dual brake systems and seat belts being standard). Apparently the seals inside that master cylinder were worn to the point that they no longer kept the front and rear systems separated, which you will never know happened, until a wheel cylinder (4 wheel drum brakes) on a rear brake failed, backing out of the driveway, and the pedal went all the way to the floor.

A lot of problems went away with hydraulic brakes when master cylinder design changed to aluminum with a plastic reservoir housing. Rust caused by the moisture damaged seals and contaminated the system, and aluminum master cylinders don't get the corrosion internally from moisture that iron ones did.

Ray-IN said:
For example, Mercedes recommends replacing brake fluid every two years or 20,000 miles. Ford says every 3-5 years.
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This goes back to what I said about DOT4 fluid being worse about sucking up moisture. Mercedes uses what they call DOT4+ (which is only available from Benz and NO OTHER DOT4 brake fluid meets Benz approval) Sprinter owners take note!!!! While Ford like almost all North American and Japanese manufacturers use DOT3 spec fluid.

Charles
 
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Nothing spells excitement like riding a motorcycle with moisture contaminated fluid, that calibers expand when hot and lock up front wheel when riding. After that episode a few years back, you bet I keep everything I own flushed every other year. I might not do the anti-lock brakes to spec on the cars and truck, but during winter I do make sure I cycle them hoping for eventual replacement. As long as my wife is the pumper, all is good.
 
Ray-IN said:
The hydraulic brake system is not closed or it couldn't absorb moisture.
Why is it All auto mfgrs recommend replacing brake fluid? Moisture in the fluid causes corrosion and when heated turns to steam, which is highly compressible. The result is greatly reduced/no braking ability.
For example, Mercedes recommends replacing brake fluid every two years or 20,000 miles. Ford says every 3-5 years.
The brake cylinder reservoir in my 13 Silverado pickup has air space above the full line = moisture laden air.
In Florida for instance, moisture in brake fluid is much more common than is AZ, NM, or NV. That means hydraulic brakes in FL require more attention.
There are many articles on the web along this line that back-up my post.
Every can of brake fluid I've ever bought says in the instructions to discard unused brake fluid if the container has been unsealed for a specified time period, usually 30 days max.
Afterthought: MH hydraulic brakes are considered heavy-use, as are medium-duty trucks.
Click to expand...

Brake fluid if hygroscopic. It absorbs moisture. Not only does the moisture effect braking performance, it also causes problems with calipers, master cylinders and anti-lock systems.
 
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