Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Silicone vs. ordinary brake fluid

About 18 months ago, I pulled a front Caliper apart. You could see the water in the pistons. Dot 4 & fluid had been changed the year before.

Sorry, but cannot quite follow the logic here.
Dave is saying that the rear cylinders often exhibit fluid far dirtier than the fluid reservoir, as moisture gets in through the seals on the brake cylinders, which I totally agree with.
But, I don't think that one can then conclude that the moisture level in the reservoir will be in any way indicative of that in the rear. They simply aren’t going to mix under normal circumstances.
So I think even if you had an acceptable moisture level from testing after say, 2 or 3 years, it would be folly not to change the fluid.
Think your original thoughts in your previous posting on the subject, virtually answered the issue.

As DOT4 is hygroscopic wouldn't the water it absorbed be wholly mixed with it Bob

Hydro = water
Philic (philos) = love
Phobic = fear

Hydrophilic = loves water

Hydrophobic = fears water

there is a limit to the amount of water that can be absorbed. Sort of like salt in the bottom of a glass of water.

I

My last +8 had silicone fluid in it when l bought it ,the same fluid in it when I sold it after eighteen years later. Never had a moment's trouble with it. Never had to top it up.

Yipee, brake fluid tester arrived

However, now comes the bad news.

I checked the exact date that I changed the fluid which was 20/1/21 so about 32 months. Over the recommended limit but not too bad certainly by most standards.

Both the brake and clutch fluids went straight into the double red >4% moisture which is the highest position on the light system and according to the instructions means Danger. Change fluid urgently.

But it could be a faulty new tester couldn't it?? So I opened a fresh bottle I had in stock and guess what. Single green light signifying <1% moisture as one would expect with a new sealed bottle.

Now, I also have some of the original 2021 bottle leftover which I had resealed and not opened since as I never needed to top up. That was also single green light <1% moisture so even though it is also 32 months old, it is still as good as new because it was resealed after use.

So, conclusions.

1. My new brake fluid tester does work.
2. Even after 32 months, i.e. only 8 months longer than recommended, the tester when off the scale. Remember all the tester shows is over 4% so it could be a lot higher.
3. I can be a bit cynical about recommended change intervals (and eat by dates) but from now on I will keep a much closer watch on fluid moisture content and change it more regularly.

As a slightly comforting afterthought, I went to Austria in September and did 2 runs up and down the Grossglocker pass and others and the brakes did work. Obviously or I wouldn't be writing this.

Yes. That sounds right. Just like Luddite. Accordingly to the brake and scentific experts, being hydrophobic, the water that enters the system will not combine with the brake fluid and not be visible. It will pool at the lowest points in each DOT 5 filled system that uses DOT 5 and without regular changes. This will be undetectable, though easily curable. Over time, the rust it creates will not be seen and it will not show up with a brake fluid tester. The system would have to be is totally flushed and carefully examined. The only other way to discover it is by eventual brake failure during usage.


Well done Bob. Good. There was a need for another lab rat like me. I have seen the same thing as you, but never that bad. However, brake fluid lasts longer in the Quebec mountains. Dryer climate. The 2 years they give is a world average, it varies from climate to climate. I saw some amazing things (for me) in my many years mogging the UK. I wasn't used to it but I learned. I even got to enjoy rain! So many varieties!

Good to know about the stuff remaining in the bottle if quickly sealed. I will take that on board for myself. What the inexpensive tester does is eliminate guess work with Glycol brake fluids.
Makes a mogger feel very much the scientist! Next time wear a white lab coat. If you check it regularly, we will have an accurate estimate of brake fluid duration for your country

gmg

RichardV6 yes I thought that, but the clear hardly viscose fluid was plain to see in the area behind the pistons. Maybe gets “boiled” out. I was surprised as I follow a well known expert in changing fluid annually.

Helpful observations, Icepack

I am going to go with my experience, internet brake lore and your last supposition.

The presence of water in the caliper pistons has nothing to do with conscientious brake fluid changes. You've got that covered. But we often have calipers their squeezing wet discs at various, often high speeds. For example, water will get between the pads, forcing us to squeeze a layer of water rather than the discs directly when we are going though a flooded road area. That is no fun, especially with the added danger of hydro-planning, a feature of a light, limited clearance care, with a large closed, area at its center.

And high pressure water water will also seep through into the caliper pistons. There are those that say that water will enter the pistons even at rest, but I can't see that.

I also think you are right and that this water will boil/burn away with regular usage. However, few Morgans are regularly used. One arrives home after a drive on a wet day and then we leave the Morgan for a long period. Ergo, no water burn off. Until the next drive, the water sits there, when it can be burned off in the normal course of regular driving. I imagine it can be assimilated with glycol brake fluid theoretically, but it is at the very ends of the fluid routing. The complaint most often mentioned it that it rusts the pistons, one of the most common causes of brake seizure along with rusted discs. Yes, you can break them free, but the ongoing damage, eventually necessitating a caliper rebuild, happens faster than mundanemobiles require. Like anything, usage is the best preservative.

So my conclusion is that cars not only need brake fluid changes, the frequency of which is determined by ambient conditions, but they also need frequent usage. Few of us can manage the latter. So we must merely resign ourselves to more frequent brake rebuilds or stainless steel caliper pistons. I use them, but I never thought of this reason before. So thank you. I swapped them in because the regular choices are mild steel, aluminum, or plastic. Plastic never thrills me and both the aluminum and mild steel corrodes along with the bores. It doesn't take a lot of work or money to tweak a trad to be fully reliable, comfortable and long lasting. That perception has changed a lot in the last 20 years, which says about the Factory than it does of us.

gmg