Brake system issue

good morning, I tried to post the other day, but don't see it. I lost my brakes while out on a 'putt'.
When mechanic opened it up, there was water in the lines, cylinders, etc. Can anyone tell me how
water can get into a closed system?
Thanks

 

As I recall the silicon brake fluid used in most vehicles is a hydrophillic (water loving) chemical, this means that it draws water molecules out of the air. This chemical property is much like what you see with lye salt and how it looks like regular salt but when it sits for a short time it draws out water from the air and looks like a white bubble...

As far as how it got into your closed system, there is just a rubber seal on the MC and a few other places like the wheel cylinders that act as a liquid seal. They aren't necessarily "air tight," meaning small molecules of water in the air can move in between those seals. It can then begin to accumulate in large amounts. Thats why its suggested to bleed brakes on vehicles every few years or so. At least thats my theory based in several college chem. courses. I'm sure someone else may have another explanation but what I stated happens over a long or short period of time depending on the wear of the seals and and sort of tear in them.

 

+1. Water from the atmosphere is a little water, which can come out of solution and make drops in the lines and cylinders. Lots of water typically means the master cylinder has been underwater - not difficult on a CJ where the MC is down at frame level.

 

If your master cylinder is still mounted on the frame rail then the water most likely entered through the vent hole in the cap as was said above. It's not truly a closed system on these Jeeps because of that vent.
DOT 3, 4, and 5.1 are all hygroscopic which means they absorb moisture from the surrounding air. DOT 5 is the silicone based fluid and is not hygroscopic.

 

Thanks to all that replied. It is a 1965 CJ 5. stock. The MC is frame mounted. (I did not know there was a vent hole.) It is a single and 9" brakes. We did a complete brake job about 8 yrs ago.......could not tell what fluid we used. I have not had it in
any deep water.
at any rate, it is getting a new MC, lines, cylinders, and shoes......just curious how it happened. Now will put it on a 'schedule' for maint.

 

Rule of thumb is to flush the brake system every 1-2 years depending on humidity, use, etc. unfortunately very few people are aware of this or they don't care so run into issues like you are having. This is why silicone fluid is popular with the street rod crowd but that has its pitfalls as well.