Silicone brake fluid warning

[lyons]

I rebuilt my 3.8 master cylinders 2 years ago and filled the new system with Silicone fluid and had no problems. Last year the pistons stuck, so the seals inside the brake cylinders were replaced and all was fine until ---

This year I noticed that both the brake fluid reservoirs had changed colour and the brakes were dead, so stripped out the brake system to find that the silicone had reacted with new seals and split into two components with water like substance on the bottom and an oil film on the top. On stripping both master cylinders it was evident that the new seals had reacted with the silicone and had rendered the brake system useless at any speed. Clutch cylinder with original seals is still OK. Anyone else aware of this issue.

[mgcjag]

Hi Lyons......Both my cars are using silicone and no problems yet.....would be interesting to know what the silicone supplier has to say on your problem......have you contacted them......Steve

[daverawle]

Is it possible to see if the seals are marked "DSL", (Dowty Seals Ltd)? These are supplied by the main sources and are not suitable for silicone fluid. I am using SBR seals which seem ok.

Dave

[christopher storey]

From your description , I doubt whether it is anything to do with the seals. It sounds as though you have something which is allowing water to get into the system. Have you been washing underbonnet or any similar procedure? The separation of water and fluid is characteristic. Unlike alcohol ester based fluids , silicon is not hygroscopic, and instead of the water emulsifying, it pools at low points of the system , such as in the master and wheel cylinders , which is what causes such damage to the metal components

[pmansson]

I tried this, as it seemed to make sense, but soon found that the brake pedal would not release immediately (for example when in an uphill slope and in front of a redlight, the car would not roll back immediately. That?s how I found out). Changed back to DOT 4 after washing the system thououghly.

[Heuer]

I know this is an old chestnut and opinions differ widely but this extract from the latest Jaguar Driver (Jaguar Drivers Club magazine) written by John Wilkinson makes for interesting reading.


Copyright Jaguar Magazine and John Wilkinson

[vipergts]

I only use silicone fluid to avoid paint damage.

I I hadn't then my car would have needed an under bonnet repaint before I'd finished the build....Fluid everywhere

[Dave K]

I tried this, as it seemed to make sense, but soon found that the brake pedal would not release immediately (for example when in an uphill slope and in front of a redlight, the car would not roll back immediately. That?s how I found out). Changed back to DOT 4 after washing the system thououghly.

After dismissing the clear instructions that came with my sleeved and overhauled master cylinders saying "Do not use silicone fluid" I did and I ended up with the same problem above plus one newly overhauled rear brake cylinder leaking fluid.

I still carried on using silicone fluid until Rob Beere changed my servo and put standard fluid in. All is OK at the moment after changing out the faulty parts.
I keep asking the question and no one can give me a satisfactory answer why do all major brake suppliers tell us not to use it? Do they know something we don't?
The camp is split, those who use it and have never had a problem and those who have either used it and have had problems or listen to the "experts".

Dave

[Heuer]

It must not be used in cars with ABS which is probably a good proportion of the vehicles on the road nowadays, hence the warning. It was developed for the military who got fed up of having different types of hydraulic fluid on their shelves and wanted to standardise on one.

Personally I see no advantage in using it underlined by the fact not a single car manufacturer in the world feel it is of value. With all those billions to spend on R&D one tends to lean towards their experience I guess. Never understood the classic car mentality which seems to be they alone have found the Holy Grail of car maintenance and longevity. I think it stems from the 1980's and the journalist at 'Practical Classics' "We will restore this Rover P60 once and it will last for 100 years"

So on the negative side silicone fluid:

1. makes brake pedal response slow
2. disrupts cadence braking
3. can damage seals
4. makes bleeding difficult
5. allows water bubbles to form
6. turns to sand if ingested into engine
7. requires regular bleeding to remove water

On the positive side:

1. does not harm paintwork

But some people get it to work (Angus, Christopher and Lee) so maybe there is a trick?

[Dave K]

It must not be used in cars with ABS which is probably a good proportion of the vehicles on the road nowadays, hence the warning. It was developed for the military who got fed up of having different types of hydraulic fluid on their shelves and wanted to standardise on one.

Personally I see no advantage in using it underlined by the fact not a single car manufacturer in the world use it. With all those billions to spend on R&D one tends to lean towards their experience!

David,

Exactly what I thought they do know know a few things when it comes to designing cars and safety.
I really don't go with the protecting paintwork bit either, it's not sulphuric acid and doesn't strip the paint on touch, it will only strip the paint if it's left on for sometime. If some gets dropped on paintwork wipe it off immediately and all will be fine.

Dave

[Heuer]

Actually if you quickly chuck water on it, being hygroscopic, it just washes away. I had some left over last year and I decided to play with it and I could not believe how quickly it dissipates in water regardless of what surface it is on - hands, brushes, plastic containers, painted metal etc. The trick is to ensure it is washed off within 10 minutes or so. As you say, it is not that fast acting on paintwork.

[christopher storey]

But some people get it to work (Angus, Christopher and Lee) so maybe there is a trick?

If it is me you are referring to, I have never used silicone based fluid - in fact I use dot 3 if I can get it, dot 4 if I can't - and of course I too have had the underbonnet paint damaged on 2 cars by osmotic hoses !

[Heuer]

Sorry Christopher for some reason (age probably!) I thought you championed DOT5. So far my new hoses are remaining osmosis free so they seem to work better than the others we tried. For anyone who is confused by 'osmotic hoses' see here:
http://etypeuk.com/forum/viewtopic.php? ... brake+hose

[Kes]

I have to say I've had it in my S2 since the car was restored - no problems at all (yet :?)

[Heuer]

I think the main lesson is to bleed the brakes every couple of years to remove water droplets from the silicone. It is not a 'fit and forget' solution.

[Joe Burghard]

When the mechanical work on my Series 1 (with a Series 2 brake system) was finished, it was filled with DOT5 fluid based on the success the mechanic had with DOT5 in his Series 3. The car sat for a number of years before the body work was finished - then the trouble started -3 failed reservoirs, failed seals in the master, fluid in the booster, corrosion in the front calipers but no paint damage. Replaced the clutch master and slave, brake master and servo, all reservoirs and inner connecting tubing and front calipers. I had already replaced the flexible brake lines with Teflon lined tubes. I continued to believe the success stories about DOT5 - perhaps it works if the car is used immediately and often. It didn't work for me.

[Moeregaard]

The only good thing I've heard about silicone-based DOT-5 brake fluid is that it doesn't harm paintwork. The big negative is that it typically contains a lot of suspended air and, as a result, makes brake system bleeding a real pain the a*rse. Some people have resorted to evacuating the fluid in a bell jar prior to use, just to get the air out.

IMHO, the silicone fluids have been marketed as a maintenance-free alternative to the DOT- and -4 fluids, but E-Types (and other cars) will benefit more from annual fluid changes rather than the type of fluid used.