Going silicone

[sparky_spit]

I'm about to change the mineral based brake fluid in my Spitfire and I'm leaning towards using silicone fluid for the 1st time in the car's life. The plan is to pump through the existing fluid using an eezibleed and refill with silicone without stripping and changing the rubber components.

Is it okay to do it this way, as it is much easier than renewing all the seals. Any thoughts or advice?

Edited May 29, 2022 by sparky_spit

[RobPearce]

You will get conflicting opinions on this one.

I have, on several occasions, done exactly as you intend. Of the half dozen cars which got silicon in both brakes and clutch, without any seals being changed, one rear slave cylinder and one clutch master suffered seal failures some time later. I should say, I tend to keep my cars quite a long time and use them extensively. The brake cylinder was on my everyday transport and the seals were probably 20 years old. The clutch was a car I'd owned for fifteen years by then (I still have it) and the problem developed at least ten years after the fluid was changed. So maybe the silicon caused the problem, maybe it didn't.

[Ed H]

I'll offer this for what it's worth.  I read it long ago from a source that seemed credible to me at the time.

Brake fluids have additives that intentionally swell rubber compounds by a controlled amount  to help with sealing.  The swelling agents in glycol- and silicone-based fluids are necessarily different, and adding silicone to a system formerly using glycol could result in some rubber parts getting double-swelled, leading to accelerated wear and failure.

I can't vouch for the accuracy of this claim, but it fits with some anecdotal evidence that we hear.

Ed

[sparky_spit]

Okay, thanks for the replies above; most helpful.  I also spoke about this with my son (1970 Mini) this morning who'd had this discussion with members of his local club (Brighton/Eastbourne area) and he confirmed more or less what you have said above.

I've decided to stick with mineral/Glycol until the next time I need to change any seals, and do the change "properly" then.

Thanks again - Mike

Edited May 30, 2022 by sparky_spit

[Guppy916]

When I restored my GT6 I opted  for silicone, and I also changed the family run about as well i think at least 5 years ago, ive had no trouble since, 

[glang]

Were the seals changed at the same time though?

Also I worry what the insurers view is...

[standardthread]

I first used silicon in both my brake and clutch lines in my Herald estate when we restored it some 35 years ago when the TSSC first announced and promoted its use. I can't remember if I replaced any seals in the systems. For a couple of decades I used it as a daily driver covering a few thousand miles per year. That fluid and seals are STILL in the car, without any issues or seals needing changing. The car has been laid up for a few years but is moved periodically without any issues with either the brakes (apart from light rust on discs etc.-I leave the handbrake off) or clutch.

Just over 5 years ago we got our Daughter a Standard 10 Companion and the first job was to fit discs, and, at the same time run silicon fluid through both brake and clutch lines, non of the seals were changed apart from the new seals in the calipers. Again, there have been no issues.

[Hogie]

Just to clarify MINERAL brake fluid is NOT used in any TRiumph.

Citroen, Rolls and many aircraft up to the late 60's use mineral  but no cars.

If you are concerned about your seals deteriorating then add mineral fluid - it will take a day  or so but you will have no brakes.

 

Roger

[Steve P]

Had silicone in my Herald and Vitesse for at least 10 years, no seal change when swapping, the only failure i had was at MOT time with a rear wheel cylinder failure, but that was only a year or 2 old, I put that down to the pony quality of the cylinders available now.

S

[glang]

Must say Im quite surprised many seem to have changed fluids over so casually - these are your BRAKES and generally single line systems so any failure and there could be big problems plus possibly some explaining to do afterwards😯

[Hogie]

16 hours ago, glang said:

Must say Im quite surprised many seem to have changed fluids over so casually - these are your BRAKES and generally single line systems so any failure and there could be big problems plus possibly some explaining to do afterwards😯

+1

[standardthread]

18 hours ago, glang said:

Must say Im quite surprised many seem to have changed fluids over so casually - these are your BRAKES and generally single line systems so any failure and there could be big problems plus possibly some explaining to do afterwards😯

That's why i ALWAYS ram the brake pedal hard when I first get in the car, before I start the engine or move the car, having suffered a single brake line failure (before I moved the car) due to a pipe rusting, either through external corrosion, and/or the hygroscopic nature 'mineral' type fluids. 

I also suffered a similar failure in a Dolomite clutch line because the cast iron slave cylinder had rusted internally specifically because of the 'mineral' fluid. And, don't they use silicon fluids in F1 cars?

Edited November 4, 2022 by standardthread

[glang]

Im not saying theres anything wrong with silicone but to just whack it in a system not originally designed for it seems to me a bit haphazard. I can imagine insurance companies having a field day if they wanted to.... 

[yorkshire_spam]

I have dot 5 in the Dolomite because it's what the previous owner used. When I drain the system to work on the rear axle I'll be flushing with meths and going back to dot 4. But I'll be checking all the seals etc well after changing over!

 

[foshi]

nothing wrong with  dot 4 on single line brakes ,   in over 40years have not had brake failure on a single line system i always check the level before driving . routine maintenance should show up leaking seals rusted pipes ect, paul

[ferny]

I had the brakes completely fail once. I was coming up to a roundabout at the end of a dual carriageway. For some reason I decided to brake far earlier than normal and the pedal hit the floor. I had to use the handbrake which somehow worked for once. That was fun!

 

The cause? I never found out. Everything got stripped and checked to find no faults. The master cylinder was about a month old.

Edited November 4, 2022 by ferny

[foshi]

must have been fluid loss ?

[glang]

1 hour ago, foshi said:

must have been fluid loss ?

No, reckon it was that little seal that should close off the reservoir when you press the pedal. Worries me on a single line system as its a tiny little thing which doesnt really give any external sign of failure - all you can hope is that it fails intermittently to start with (so stamping repeatedly on the pedal returns the braking) and you can change it asap...

[ferny]

6 hours ago, foshi said:

must have been fluid loss ?

 

4 hours ago, glang said:

No, reckon it was that little seal that should close off the reservoir when you press the pedal. Worries me on a single line system as its a tiny little thing which doesnt really give any external sign of failure - all you can hope is that it fails intermittently to start with (so stamping repeatedly on the pedal returns the braking) and you can change it asap...

In reply to me?

 

Honestly, no idea on failure. Fluid? Fine. Strip down and inspect? All fine.

 

Happened in 2020 in February. I'd changed the master cylinder at the beginning of January. I can remember those details due to life events at the time and it shitting me up quite a bit!

[glang]

Yes and in your case its the only possible explanation - even a close visual inspection of said seal can be inconclusive. Then perhaps just debris getting under the seal temporarily could stop it from doing its job properly...

[Hogie]

23 hours ago, standardthread said:

That's why i ALWAYS ram the brake pedal hard when I first get in the car, before I start the engine or move the car, having suffered a single brake line failure (before I moved the car) due to a pipe rusting, either through external corrosion, and/or the hygroscopic nature 'mineral' type fluids. 

I also suffered a similar failure in a Dolomite clutch line because the cast iron slave cylinder had rusted internally specifically because of the 'mineral' fluid. And, don't they use silicon fluids in F1 cars?

EVERY body - please, please, please stop calling DOT4   MINERAL  it is NOT. It is a synthetic oil based on Glycol-Ether.

https://en.wikipedia.org/wiki/Brake_fluid

Very few cars use Mineral oil (no DOT  Spec - however Aerospace is DTD585)

If you put mineral oil in our cars then your seals will fail quickly - honest.

Although DOT5 Silicone is not     Hygroscopic    Hydroscopic  it will take on water as does any liquid open to the elements.

Your pipes can still rust.

Roger

Edited November 5, 2022 by Hogie

[standardthread]

1 hour ago, Hogie said:

EVERY body - please, please, please stop calling DOT4   MINERAL  it is NOT. It is a synthetic oil based on Glycol-Ether.

https://en.wikipedia.org/wiki/Brake_fluid

Very few cars use Mineral oil (no DOT  Spec - however Aerospace is DTD585)

If you put mineral oil in our cars then your seals will fail quickly - honest.

Although DOT5 Silicone is not     Hygroscopic    Hydroscopic  it will take on water as does any liquid open to the elements.

Your pipes can still rust.

Roger

That's why I put mineral in parenthesis.

Extract from the Oxford dictionary;

"hygroscopic 1. Of a substance: tending to absorb moisture from the air. L18. 2. Pertaining to humidity or its detection. L18. 3. Of water: present as moisture in soil as a result of humidity in the air to which it is exposed. M19.

hydroscopic  [f. HYDRO- after hygroscopic.] = HYGROSCOPIC 3." unquote.

 

[Hogie]

Hi Stan,

you are correct  about Hygroscopic.   

However people do not read the punctuation just the words.

It is  not mineral in  any form.

 

Roger

[ferny]

39 minutes ago, Hogie said:

Hi Stan,

you are correct  about Hygroscopic.   

However people do not read the punctuation just the words.

It is  not mineral in  any form.

 

Roger

Oh, so it's a vegetable? We're meant to use vegetable oil for braking systems? 

 

I'm off to the chippy for a brake service! And maybe a cheeky sausage. 

[Hogie]

Put whatever you want in your brakes.

 

Good bye.