I'm thinking about this for my clutch. I know it's not as good at resisting boiling or foaming or as firm, but none of these are much of an issue on the clutch.

I pulled a 3-yr old clutch slave cylinder out and the thing was corroded to hell from moisture trapped in the Dot 3. So I'm thinking silicone may be the way to go?

I'll consider putting it in the brakes too, since I don't have ABS.

When I replaced my master cylinder last year, I used the synthetic stuff, thought it was DOT4.

I'm not sure, and of course the car isn't here right now (I have the bottle in the back storage compartment).

But anyhoo, I did the swap-out in spring last year, and it worked fine last season; no leaks or deterioration rubber on the gaskets or boots , that I could tell.

I'll take a look this coming Sunday, and let you know what it actually was (I know the brand was STP)

Dot 4 is a replacement for Dot 3, still aquaphilic(?), but with a higher boiling temp.

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You're right.

I re-read the thread headline, and I know for sure it wasn't silicone based. So now I'm quite sure is was just run-of-the-mill synthetic DOT 4.

DOT 5 can cause servere localized corrosion if it gets airated apparently.

DOT 5 is best for storage. Otherwise, don't use the crap.

I would use DOT 4 - I highly recommend Valvoline Synpower - and bleed it annually.

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I'll check on it... but I don't see how aeration is gonna happen in a non-ABS brake system or a clutch system.

I use it in my old 1930 with hydraulic brakes and it works fine for that- went like 20 years before rebuilding system. Even then I did it just for peace of mind. I also think it would do fine in the clutch system. Not sure if it would work well in a disk brake system even without the ABS.

I'm gonna use it in the clutch regardless, and I'll show you guys why in a new thread in tech later...

I THINK DOT 5 WILL SERVE YOU JUST FINE CENTRAL...ALL USPS VEHICLES USE DOT5 & THEY HAVE MINIMAL BRAKE SYSTEM PROBLEMS...I HAVE WORKED ON ALL OF OUR LOCAL POST OFFICES LLV'S FOR THE PAST 8 YEARS & HAVE NOT YET HAD TO REPLACE A MASTER CYLINDER, WHEEL CYLINDER OR CALIPER--JUST PADS & SHOES.

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No you wouldnt think so, although if you happened to get a pulsing pedal it might.

You should be right, but then you wont ever know if you dont try it mate, and if it does serious damage, we will know you shouldnt have tried it!!
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Id want to bloody hope you hadnt had to replace any of those items in only 8 years, they should last alot longer than that.

I'd be thrilled to get 8 years out of any of these shitty aftermarket cylinders.

I'm going on my 3rd master and 3rd slave in 6 years, and they've seen plenty of fresh fluid.

The U.S. military also uses Silicone brake fluid. Every Army HMMWV (Humvee) comes with it (in four wheel disc brakes). It also came in the CUCV series vehicles (K5 Blazer and K30 one ton pick-ups) procured from 1984-1987.

We also converted M151 Jeeps, M35 Dueces & half trucks with four wheel drum brakes back in the early eighties. Just be sure to purge fully (we use methenol alcohol) or they mix of silicone and mineral (dot 3) turns to goo.

I do know that silicone tends to be a little thicker and air bubbles tend to stay in suspension longer. 'Think that's why it's incompatable with ABS. Worse case you get a spongey clutch pedal after awhile, then you change back.

I ended up putting Dot 4 in there.

I was reading mixed reviews about how the orings stand up to the dot 5.

So far so good.

I still need to post pics of the slave cylinder I removed, It's corroded to hell.

Never ever ever use the DOM Raybestos/Delco ZF clutch cylinders.