Silicone Based Brake Fluids

[Hunter2]

Are silicone based brake fluids compatible with brake & clutch masters, clutch slave, calipers and brake cylinders?

Here in NA, ID'd as DOT 5, fully synthetic.

[woodypup59]

I have used them for decades in 5 cars without problems, other than a slightly softer pedal.

[Spider]

Hey Rick, I have it in one car and had no issues, but that was filled from new with it. Most suppliers of the fluid warn that all rubber parts of the system must be new.

Be aware, many of the manufacturers won't warrant they parts if silicon fluid is used.

Pete loves it, I'm sure he'll be along soon.

[Peter Laidler]

Peter here, just as Spider Chris said he'd be!!! I've been using silicon brake fluid since Archangel Gabriel invented it! Silicon fluid is one of those taboo subjects on the forum, so I'll keep my voice down.......... I'll let you into a secret too.

I bought a brand new Rover Cooper Sport in the olden days and after a few weeks, drained the old stuff out as best I could and filled up with silicon. No doubt - and in fact - there was some of the old stuff in the system. The two liquid will not integrate, they won't mix. The standard stuff will always float to the surface. For the first couple of years there was always a small amount of the clear standard stuff that had made its way to the top of the plastic master cylinder. I'd syphon it off, bin it and top up with silicon. Been perfect from day one

Been using it in all of my cars, MG's, (REAL MG's and not the modern Chinese stuff) VW's and Cooper S's brake AND clutch ever since

[InnoCooperExport]

Much like Peter I run it in all my classics. Initially only the MGA then when the master cylinder in the Lancia failed we went silicon on the rebuild and I just built up and filled the Innocenti with DOT5 silicon. And I'll say when it leaked everywhere because I hadn't quite pinched up the unions tight enough I was pleased it was silicon.

[Alex]

It's mildly compressible, so very light brake applications may fail to activate a hydraulic brake light switch; I've seen this on quite a few cars in convoy.
You may need to retro fit an electrical switch if you don't already have one.

[Peter Laidler]

Sorry Alex and any other doubters, it's not any sort of compressible. It's a basic fact of physics that you simply cannot compress a liquid. If the brake light - or anything else fails, then it ain't due to a compressible liquid.

Physics teachers hat on now, but two good examples of the incomprehensibility of a liquid are Tsunami's and torpedo detonations.

[Alex]

Sorry Alex and any other doubters, it's not any sort of compressible. It's a basic fact of physics that you simply cannot compress a liquid. If the brake light - or anything else fails, then it ain't due to a compressible liquid.

Physics teachers hat on now, but two good examples of the incomprehensibility of a liquid are Tsunami's and torpedo detonations.

"Is silicone brake fluid compressible"
https://www.google.com/search?q=is+sili ... s-wiz-serp

Even a basic Google search shows that silicone brake fluid is compressible.
Penrite who make the stuff state it's three times more compressible than normal brake fluid - https://penriteoil.com.au/knowledge-cen ... -fluid/307

(Water isn't, so your examples stand for tsunamis and torpedos)

[Peter Laidler]

PM sent Alex. But the scientific/laboratory definition of 'comprehensibility of liquids in real life was discussed on the forum a couple of years ago.

[GraemeC]

I think the key is that a fluid that is silicon based is not a true liquid. It’s more like a very very soft plastic blended with all sorts of other stuff and no doubt has air held inspensuon in it.

“In practice, this means they can compress up to three times more than conventional fluids when pressurised”

[InnoCooperExport]

PM sent Alex. But the scientific/laboratory definition of 'comprehensibility of liquids in real life was discussed on the forum a couple of years ago.

I was going to say. I remember this discussion. I believe I brought up the compressibility of mixtures of solvents which I used to deal with in analytical chemistry when I was still in the space industry. But then I was working just south of 600 bar and would have gone higher if my pump allowed it! And even then we were talking about compression in the order of 10^-6 per bar. Not something I worry about or really notice with the silicon fluid in my brakes.

[Peter Laidler]

Thanks for that clarification Inno. And I agree. In the mechanical engineering world/terms such as in our cars and in my previous experience, it's all a matter of semantics - or word play. In this case compressability that only exists under laboratory conditions..

[Spider]

As mentioned, I only have it in one car. I have to say, if it does compress, I can't notice it.

[68&86auto]

“In practice, this means they can compress up to three times more than conventional fluids when pressurised”

That doesn't mean it's compressible to any noticeable level. 3x close to nothing is not much.

That's just my thoughts from reading your quote. I have no knowledge about how much either actually compresses but I can't imagine it being much at all.

[Peter Laidler]

You're right 68 and 86. In the REAL world of engineering as we know it and in my days at uni and teaching, it's always been a rule of physics that you can't compress a liquid. I like your statistical analogy too, that 3x close to zero is not a lot!

It's been a rule of thumb on the forum, like your club, mess, common room or lodge that you never discuss or raise the subject of religion, politics, waterless coolant and silicon brake fluid!

[roger mcnab]

hi pete
what else is there to talk about everything else is boring if we can not talk about the pm and the president life would be dull but i guess minis are a good backstop
cheers roger

[Spider]

I know in recent times they moved away from it, but only as cost cutting, however Harley Davison used it from new in their bikes for a very long time and the US Army too used it for a very long time.

[Peter Laidler]

We used to send most of our oils and liquids away to be filtered, cleaned and re-used. It used to come back in 40 gallon drums with certificates of SAE spec and purity etc etc. Including brake fluids - both types

[BAD942B]

one thing that changing brake fluid does whichever type you use is flush all of those tiny bits of rubber pulled off the seals whenever you press the brake pedal out of the system, taking 1/2 ltr through every year makes the seals last longer

[cobolman]

Been using it in all of my cars, MG's, (REAL MG's and not the modern Chinese stuff)

I wondered if you were THAT Peter Laidler from MG circles. Now I know!

My other car is a 1974 MGB GT V8. A 'proper' MG, as you say

And as to silicone brake fluid, I've toyed with the idea a while. Following your comments here, I may just fill Marty the Mini with it (when it's done)