Replacing DOT 4 with modern silicone brake fluid?

[rolesyboy]

Just rebuilt calipers, brakes etc all dismantled and wondering whether to replace my brake fluid with this silicone stuff. Is it worthwhile and if so do I need to empty every drop of DOT4 or is it a case of new cylinder rubbers etc. I gather that the silicone stuff is less harmful to paint etc. Cheers. Mark

[surfblue63]

There's a lengthy article on the Moss web site about brake fluids.

http://www.mossmotors.com/forum/forums/ ... 10403.aspx

Here's a small extract regarding changing from DOT4 to Silicone

A newly rebuilt and scrupulously clean brake system filled with silicone fluid should outlast a system filled with glycol fluid by several times. There is little advantage in adding silicone fluid to a system which contains even small amounts of contaminants. Merely bleeding the system is not enough, as there will be pockets of old fluid and sludge which will not bleed out. Silicone fluid tends to concentrate any residual glycol fluid, moisture and sludge, into slugs, instead of allowing their dispersal throughout the fluid, as does glycol fluid. This can lead to relatively severe but localized problems, rather than the more general system deterioration experienced with old moisture-laden glycol fluids. This may be a factor in reports of leakage when silicone fluid is used in non-rebuilt systems which had been used with glycol fluid. A "new" system full of silicone fluid will require very little maintenance for years.

[pad4]

ive been strongly advised against using silicone fluid in a mini due to compatability with the rubber seals in the system - just go for a good race quality dot 4

pd

[Chalkie]

It be fine if you used all new brake lines and cylinders

[Tim]

I've heard from at least two sources that the hydraulic brake light switches on Minis fail very quickly from silicone fluid.

Tim

[Chalkie]

I've heard from at least two sources that the hydraulic brake light switches on Minis fail very quickly from silicone fluid.

Tim

Mine never worked anyways wouldn't make much difference

[timo]

I have run silicone fluid in the barkes and clutch on a Mini for the past 15 years and wouldn't use anything else.

The fluid was used as part of a re-shell build that included all new brake components, including the brake lines.

About 3 months after the car went back on the road, one of the caliper seals failed. After much checking, this proved to be a faulty seal and not a fault of the fluid.

Since then no problems and the brake pedal has been very good.

I now run it in my Frogeye and MGB and again no problems.

[steady eddie]

ive been strongly advised against using silicone fluid in a mini due to compatability with the rubber seals in the system - just go for a good race quality dot 4

pd

Stick to good quality dot 4 but change it frequently, we race on it, Millers Oils make a good one.

eddie

[graham in aus]

I too have cars with long term usage of silicone fluid, my Mk1 S 'bitsa' has used it (DOT 5.0) for 12 years following full rebuild. No seal or cylinder failures and great pedal! I have used this car for some competition work too.

Other car is for hillclimb / sprint, 6 years no issues, again though, silicone used from day one, no mixing.

I have not tried it for the ultimate brake testing i.e. circuit racing, I use Dot4 in my race car, but I have considerd trying it!

Silicone fluids are very 'inert' and should not attack seals. I have had several brake light switch failures on other (non silicone) cars, I think the new switches are rubbish, fitting older (used) ones is the answer!

I think this is what you guys call a 'Marmite issue' !!

I buy silicone fluid down here from Harley Davidson dealers, they use it in their bikes......

[graham in aus]

Interestingly it appears that DOT 5.1 fluid is not silicone, only DOT 5.0

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

5.1 looks to have matched silicone fluid for temperature performance.

Bit of a nightmare for not mixing them up!

I might try to find some 5.1 for my race car.

[mk1]

I have used Silicone in all fully rebuilt systems for years, have not had any problems & would never go back to the stuff that rots your paintwork.

[LMM76C]

Silicone brake fluid has the fundamental problem that it does not absorb water in the way conventional brake fluid does.
Good then?
No. Water (from condensation, if nothing else) WILL get into the system to some degree. As hinted at in an article above concerning residues, with silicone it will not mix and will therefore boil under hard use.
For that reason alone, silicone is most certainly a very bad idea for motorsport use. Even a very short hillclimb that does not stress the brakes much is risky if you happen to need them just when a bit of unabsorbed moisture is at a critical point in the system.
Obviously non-silicone fluid (even competition stuff like Castrol SRF or the period "Girling Green") will deteriorate as it gradually absorbs moisture but consistent deterioration (avoided by changing it) is prefereable to sudden loss of braking as unabsorbed moisture reaches the vital parts.

[Fanfaniracing]

My experiance, as i worked in a mini specialised garage for some 5 jears, was that the guys who had filled their system with this silicone fluid had more problem with their system that the ones with normal DOT 4 or so.

the problem is that sylicone brake fluid, as posted from LMM76C, don't mix with wather. silicone brake fluid has a less density as wather, so it "swimms" over the wather.

in result of that the wather goes to the deepest point in system so brake calippers and wheel cylinders stick if the fluid is not changed regulary...

i prefer to change my brakefluid every jear than filling it up with silicone fluid as in my opinion its saver.