A few pages back the question was raised as to how moisture gets into a sealed brake system. Well it turns out that brake systems are sealed against brake fluid leakage ---- not moisture absorption.

I know this because I have a brake fluid removal and replacement device that pressurizes the brake system to 4 to 10 psi at the fluid reservoir cap. Exceed that pressure and you will hear air escaping around the seams of the reservoir.

It therefore follows that air that can get out can also get in, given the propensity of brake fluid to absorb moisture in the reservoir and also around the seals in the brake pistons.

Ergo, modern brake fluids don't absorb moisture as much as the older formulations.

 

I suppose if the master cylinder was subjected to 4-10 psi during normal operation you might have a point. But it isn't.

 

So your point is that the brake system is sealed air tight? Pray tell where the water/moisture comes from and why all this palaver about water getting in the brake fluid?

The fact is, that at any pressure, air molecules are smaller than whatever molecules make up the brake fluid and they find their way into the system past seals on the pistons and master reservoir that are not air tight.

Just trying to shed some light on the subject, your cute rejoinder re air pressure not withstanding.

 

If this was true, then the brake pedal would become soft and the system require bleeding to expel the air. I've never had such a thing.

 

Forgive me for playing word police but it is hygroscopic.

Also: The size of air molecules matters not. It is the size of water molecules which are much smaller than air and are carried between the air molecules. The main source of moisture is from taking the cap off. Any other source is negligible. That's why most systems have a sight glass. Don't take off the cap unless you are going to top off.

Don't buy a large bottle to top off. As soon as you break the seal it will become contaminated. I keep a very small bottle and discard the remainder as soon as I use it.

One other trick is to use nitrogen to displace the air in the bottle if you have it available. Or the Gas in your TIG welder.

Eddie 04 VDP

 

Spoke with an ASE tech today who told me the fluid Jaguar uses is of a synthetic formulation that is not as hygroscopic as regular fluid and therefore has a longer lifespan. He also confirmed the systems are not as "sealed" as one might think and moisture can get in through the filler cap.

 

Did you buy any swamp land?

 

I have had a "soft pedal" in every vehicle I owned or operated over an extended period. It takes place slowly over several months, allowing you time to adjust to pedal travel. I have rebuilt many brake systems that were owner/operator neglected to a point of not being able to bring the vehicle to a complete stop.

Examples of neglect I have found:
No lining on brake pads
No brake fluid in the reservoir
No engine oil on dipstick
Squirrel or rat's nest in the engine bay
Rats nest in the air cleaner.
Dead cat in the engine bay.

 

The above has always been my "take" on this issue and no I have never bought any swamp land. Smart comments to the contrary, of course the brake system is not perfectly sealed against moisture. It's amazing how many people rage against the obvious.

 

All brake fluid is synthetic, irrespective of brand name or DOT rating. There is no such thing as non-synthetic or 'regular' fluid. Your tech should have known this. Did he specify how the moisture gets in, or just make an all encompassing statement that 'it just does'.

 

Just to establish some perspective this is a test for Mikey:

The sun comes up in the East

I have bets on how you will respond.

 

Looks like you have resorted to making a few smart comments of your own. Aside from heading towards troll-land, do you have a point?

 

I'm bored. Let's argue about Dex Cool.

 

Sorry guys and Mikey too. I just had to take the shot. I'll try harder to be nice in future. But God did I win a lot of money.

 

Umm, no you didn't. I enjoy coming to this board for healthy technically-oriented debates, not to take personal shots at people.

 

I'll bite...

 

Found a good brake fluid for $70, going to flush the system again tomorrow.