Any reason not to use silicone brake fluid?

[The_Eric]

I'm finally starting to pick at my '78 KZ650. One of the things that needed attention was the reservoir. Well once I got that off, I decided to go all the way and clean out all the garbage that has built up inside.

Come to find out, the bore is fairly pitted, so I'm going to hunt for a replacement. Not wanting this to happen again (or really deal with regular brake fluid in general), I'm pondering the use of silicone brake fluid. For the record, I'm aware of the cautions of installing it in a system the previously held "regular" brake fluid- it will be thoroughly flushed, in fact I'm sure I'll end up rebuilding the caliper too.

 

[Driz]

You may be able to grind out the pits with a small bore stone set on a drill. It depends on how deep they are but might be worth a shot if you have problems getting new or good used one.

 

[ARCOgraphite]

I think the whole braking system, especially the rubber and poly parts and hoses, has to be designed for Si fluid. I don't think this is a problem-free interchange.

I would Just bleed the system every couple years, Dot 3 is hygroscopic.

 

[bmwpowere36m3]

Most rust issues, as related to brakes, are due to poor maintenance... i.e., not flushing/bleeding brake fluid every 1-2 years. I guess I've been lucky and haven't had any major issues with rust in 20-30 year old cars and motorcycles. While silicone isn't hydroscopic, any water that makes its way into the system would likely separate out and settle at the bottom of the system (i.e., calipers).

 

[CT8]

Go for the silicone try it out the brake feel may be different and if you do not like the silicone drain it out and use doe 3 or 4 .

 

[Cujet]

Originally Posted By: The_Eric
Not wanting this to happen again (or really deal with regular brake fluid in general), I'm pondering the use of silicone brake fluid. For the record, I'm aware of the cautions of installing it in a system the previously held "regular" brake fluid- it will be thoroughly flushed, in fact I'm sure I'll end up rebuilding the caliper too.


I use silicone brake fluid in just about everything I fully disassemble and clean. I even (very sparingly) use Dow Corning DC-4 (a silicone O-Ring lube) to assemble the brake parts.

I've had stellar results with it. Zero corrosion problems, zero seal failure issues and it lasts seemingly forever. I love the stuff.

HOWEVER, I never use it in a system that has old seals. I use all new seals.

People that have issues with silicone brake fluid are, I guarantee, using it in old systems. And, they don't lube the seals with DC-4 prior to assembly. I feel this is key, as DC-4 is completely inert, a good O-Ring and seal lubricant, and prevents seal damage during assembly.

 

[Cujet]

Just wanted to add, my Suzuki SV1000s has "known" issues with the rear master cylinder failing and the brake pedal being largely ineffective. Mine failed multiple times on the previous owner. They replaced the master cylinder with new each time. And each time it lasted a year. (I suppose bleeding it every 3 months would also have solved the problem)

I purchased the bike with a failed rear master cylinder.

I purchased an overhaul kit, resealed both the master cylinder and the caliper. Used Silicone brake fluid and the system is now and has been 100% trouble free.

The reason: No more internal corrosion on the very small parts.

 

[Cardenio327]

I'm not sure, but I think I might have heard that silicone brake fluid needs to be flushed and bled once a year because it is not hygroscopic.

It is used in museum cars because it will not lift the paint if it gets spilled.

It is sometimes used in Russia and Finland, and in military vehicles for extreme cold conditions.

Some Harleys supposedly came with it new.

Personally, I would use a quality DOT4 fluid and flush and bleed every two years.

 

[Cujet]

Originally Posted By: bmwpowere36m3
Most rust issues, as related to brakes, are due to poor maintenance... i.e., not flushing/bleeding brake fluid every 1-2 years. I guess I've been lucky and haven't had any major issues with rust in 20-30 year old cars and motorcycles. While silicone isn't hydroscopic, any water that makes its way into the system would likely separate out and settle at the bottom of the system (i.e., calipers).


Yes, it's true that "IF" water enters a silicone based system, it will settle to the bottom of the reservoir or caliper (depending on design). I've never seen this on properly sealed systems. In fact, most motorcycle systems have a "bladder" under the cap that moves as the fluid is depleted. Thereby preventing moisture ingestion.

As a general rule, silicone based brake (and clutch) systems experience zero corrosion.

People often say that silicone based systems do feel (just slightly) softer in some cases. This can easily be fixed by using stainless brake lines instead of rubber. I honestly can't tell any difference in feel on "tight" and properly bled systems. I suspect improper bleeding in many cases. Silicone is more viscous and it takes more time to get the bubbles out.

 

[Jarlaxle]

Only caveat: do not use silicone brake fluid in an ABS system.

 

[440Magnum]

Silicone brake fluid is lower lubricity than conventional, so typically its verboten in ABS systems where the pumps and valves require a lubricating fluid. Other than that, see the comments about moisture that others have made- if none of that is an issue then it might be a good choice. Personally, I prefer the low-moisture-activity DOT4 fluids that are on the market for their wider range of compatibility, and the fact that they do still absorb and disperse moisture that might get into the system. Their advantage is they don't practically suck moisture out of ambient air the way DOT3 fluids do. I consider them a good all-round compromise.

 

[bmwpowere36m3]

Other than maybe cost... I wonder why we don't see more silicone "systems" in newer vehicles. I would think ABS systems could be engineered to work with silicone fluid.

Personally I just use quality DOT 4 fluid in all my vehicles and flush is regularly... never had any problems. Even if you spill some, if you clean it up quick it won't damage paint.

 

[The_Eric]

Originally Posted By: 440Magnum
Silicone brake fluid is lower lubricity than conventional, so typically its verboten in ABS systems where the pumps and valves require a lubricating fluid. Other than that, see the comments about moisture that others have made- if none of that is an issue then it might be a good choice. Personally, I prefer the low-moisture-activity DOT4 fluids that are on the market for their wider range of compatibility, and the fact that they do still absorb and disperse moisture that might get into the system. Their advantage is they don't practically suck moisture out of ambient air the way DOT3 fluids do. I consider them a good all-round compromise.



Interesting- I'll have to look into that. Maybe a worthy alternative?

 

[bmwpowere36m3]

Originally Posted By: The_Eric
Originally Posted By: 440Magnum
Silicone brake fluid is lower lubricity than conventional, so typically its verboten in ABS systems where the pumps and valves require a lubricating fluid. Other than that, see the comments about moisture that others have made- if none of that is an issue then it might be a good choice. Personally, I prefer the low-moisture-activity DOT4 fluids that are on the market for their wider range of compatibility, and the fact that they do still absorb and disperse moisture that might get into the system. Their advantage is they don't practically suck moisture out of ambient air the way DOT3 fluids do. I consider them a good all-round compromise.



Interesting- I'll have to look into that. Maybe a worthy alternative?


I'm wondering if he's referring to high "wet" boiling point DOT 4 fluids...

 

[CT8]

As usual Cujet is 100% correct.

 

[BusyLittleShop]

DOT 3 DOT 4 and DOT 5.1 are Glycol based brake fluids whereas DOT 5
are Silicone based... Glycol based fluids are designed to signal
moisture contamination... the fluid will start to turn golden, then
light brown, indicating that it has absorbed progressively more
moisture. Eventually, if left unchanged beyond the recommended service
interval, the fluid will become dark brown, indicating high amounts of
water absorption and thus badly contaminated fluid... user friendly
Glycol based fluids also reduce the effect of both corrosion and
compressibility because it is not only designed to accept significant
amounts of moisture, but even to neutralize it by dispersing this
moisture evenly throughout the system, thus preventing its
concentration in any one area...


Boiling point of Glycol based brake fluids
DOT 3 205 °C (401 °F)
DOT 4 230 °C (446 °F)
DOT 5.1 270 °C (518 °F)
If you wish to use the latest in Glycol base fluids then its DOT 5.1

Silicone Brake Fluids

DOT 5 Silicone based fluid will not turn color to signal moisture
content...
Boiling point of Silicone based brake fluids
DOT 5 260 °C (500 °Silicone Brake Fluids

In years past, all brake fluids were glycol. Then D.O.T. 5, a silicone
fluid having a higher temperature rating, emerged, initially to meet
the higher boiling point requirements of racing use. (Race car brake
systems include oil-cooler-like heat exchangers and ceramic pads.)
Silicone fluid was able to withstand the most heat of any brake fluid,
so it earned a reputation as a racing brake fluid. However, silicone
brake fluid has properties very different from glycol fluid, and has
its own pros and cons. On the advantage side, silicone fluid will not
harm paint or plastic, and does not aggressively attract additional
moisture as glycol fluid does. On the disadvantage side however,
silicone fluid aerates easily. Harley-Davison, one of the sole current
OEM users of silicone fluid, warns buyers to let the fluid sit at
least an hour before using it. The trip home in the saddlebag is
enough to aerate silicone brake fluid until it looks like a freshly
poured soft drink. Silicone fluid is also slightly more compressible
than glycol fluid, does not change color to tip the user to its
moisture content, and worst of all, neither accepts or disperses
moisture, making systems using it more corrosion prone, and requiring
much more frequent fluid changes. Silicone brake fluid also lacks
glycol fluid's naturally occurring lubricity, making it incompatible
with the mechanical valving in some antilock braking

 

[The_Eric]

BusyLittleShop- thank you for taking the time to chime in- definitely food for thought.

Cujet's very positive experiences are pretty hard to ignore.

One question I have is this- I see mention that there is no indication of water ingestion when using silicone brake fluid which requires yearly flushing- but really, how big of an issue is it? The braking system is sealed shut and since silicone doesn't attract and absorb water like a sponge on crack, so how much moisture/water will accumulate? I'm having a hard time understanding how what amounts to a sealed hydraulic system will get that much water in that little time.

 

[bmwpowere36m3]

Originally Posted By: The_Eric
BusyLittleShop- thank you for taking the time to chime in- definitely food for thought.

Cujet's very positive experiences are pretty hard to ignore.

One question I have is this- I see mention that there is no indication of water ingestion when using silicone brake fluid which requires yearly flushing- but really, how big of an issue is it? The braking system is sealed shut and since silicone doesn't attract and absorb water like a sponge on crack, so how much moisture/water will accumulate? I'm having a hard time understanding how what amounts to a sealed hydraulic system will get that much water in that little time.


The same could be said for glycol systems... even though the system is "sealed" it isn't 100%. I bet moisture gets into to system during cool-down, when the fluid is thermally expanded and begins to contract. Granted most, if not all, systems have bladders or room for expansion/contraction in the reservoir.

 

[Cujet]

I don't generally bleed silicone brake systems at all. It simply seems to last a very long time.

I've not experienced any corrosion issues with it.

However, I must add that I've never used it in an ABS system. Mostly motorcycles, vintage race cars and classic cars.

 

[BusyLittleShop]

Originally Posted By: The_Eric
BusyLittleShop- thank you for taking the time to chime in- definitely food for thought.


You're welcome... I agree with bmwpowere36m3 answer to your question...