silicone brake fluid

[Calvin C.]

I have searched the archives and find very little on silicone vs regular brake fluid. You read in the catalogs that silicone saves brakes from rusting, but I have also been told silicone holds air, and can have water pockits that could freeze. I am replacing all calipers and leanining twards the good ol stuff. What is the way to go from you guys who have experience. It will be a dailey drive.
Thanks in advance
Cal

[Michael W.]

Re: silicone brake fluid

There's plenty of stuff in the archives, at least 40 entries in each volume. Just search using the key word 'silicone'.

What you'll find is that neither fluid is perfect, each has it's good points and bad points, pretty much as you have summarized yourself. Boils down to a tastes great/less filling type debate, but I'm sure somebody will chime in with a post insisting that their particular favourite is a clear winner.

[Duke W.]

Re: silicone brake fluid

Silicone fluid is an excellent way to go, BUT in order to have a successful installation you must start with a system that is clean and dry. In addition, the m/c and calipers must be rebuilt and assembled with silicone fluid. You do not want a trace of glycol fluid in the system.

All metal brake tubes should be thoroughly flushed out with denatured alcohol and dried and all rubber hoses should be replaced.

Trying to convert to silicone fluid using the "bleed to flush" method is the source of most silicone fluid problems. Silicone fluid is not miscible with glycol fluid and has a different specific gravity, so there is no way to completely flush it out by bleeding.

The primary advantage of silicone fluid is that it does not absorb moisture, so in the long run your hydraulic system will probably last longer. Glycol fluid should be changed by flushing a quart of fluid through the system every couple of years. Silicone fluid should also be flushed, but perhaps only every four to eight years, and longer intervals are acceptable is the car is not driven in the rain.

Disk brke systems have a propensity to draw in air at the calipers, especially if there is rotor runout, and in the process, moisture can be drawn in also, and since water is not miscible with silicone fluid it will remain localized and cause corrosion.

My recommendation if you are rebuilding all calipers is to go the extra distance - rebuild the m/c and calipers, assemble them with silicone fluid, flush all the lines and use silicone.

As far as the "air problem" I can offer the following anecdotal evidence. A friend who worked in a university lab took beakers of both silicone and glycol fluid, shook them up and allowed a few minutes for each to settle, then drew a vacuum on each beaker and did not see any air bubbles come out of solution for either type.

Duke

[Christopher R.]

Re: silicone brake fluid

There's lots in the archives. Look some more.

Most of the people who converted to silicone did so when they completely replaced their brake system. I mean steel lines, flexible lines, wheel cylinders, etc. - everything.

Big advantage of silicone is that it requires less maintenance than glycol. Glycol systems should be flushed every 2 years. Hardly anybody does that. But if you did, you'd take away a big reason for switching.

There have been reports of problems with silicone at high altitudes. Do you think that the car will ever see the Rockies? If not, that potential silicone problem goes away.

I converted to silicone many years ago because I was replacing the complete braking system and because I did not want any more work on the car than I was already doing. But brake bleading is an easy task. Make sure you put Easybleeders in or anti-seize on the bleed screws.

[Clem Z.]

Re: silicone brake fluid

my 1988 chevy pickup has the same fuid as was installed at the factory.it was 13 years old and has 96,000 miles,the M/C cap has never been removed because i think that is where all the problems come from with std brake fluid. i have never had any wheel clys leaks or any thing. if you have no leaks you never have to mess with std fluid. JMHO

[Calvin C.]

Re: silicone brake fluid

I searched for the last 24 months using silicone as the key word and did not find harly anything. Just like my luck in Vegas.

[Calvin C.]

Re: silicone brake fluid

I just figured out what is was doing wrong with my archive search. Computers!

[Joe L.]

Re: silicone brake fluid

Duke-----

I performed a comparison test conducted almost exactly like the one that your friend performed. I came up with exactly the same results, too. I noted ABSOLUTELY no difference in the retention of air in either fluid. I really think that the air retention issue is, for all intents-and-purposes, a myth.

[Duke W.]

Re: silicone brake fluid

My conclusion too, Joe. I think the stories about air coming out of solution driving over Loveland Pass are just bloody bad bleeding.

Duke

[Duke W.]

Re: silicone brake fluid

Forgot to mention that my friend (another Cosworth Vega owner) did a miscibility test, which, of course, showed that silicone and glycol fluids are not miscible.

He also determined that the specific gravity of silicone fluid is 1.4 and glycol based is 0.95.

I ragged on him to do a viscosity test at zero degrees F, 70 F and 200 F, but he didn't have the equipment to do it.

Do you have any viscosity data?

Duke

[Calvin C.]

Re: silicone brake fluid

I was doing something wrong in my search, blame it the new computer, all OK now and finding info.
Thanks

[Joe L.]

Re: silicone brake fluid

Duke-----

No, I'm afraid that I don't have any QUANTITATIVE viscosity data relative to the two fluid types. However, based upon sheer observation of the fluid types and properties as noted in a glass vial, I really don't think that there is an appreciable difference in viscosity. I used to think that silicone fluid was considerably more viscous. I don't anymore, though.

[Duke W.]

Re: silicone brake fluid

One of the stories that has floated around is that silicone fluid is "more viscous" so it "reacts slower" - analogous to a heavier SAE grade oil flowing slower during cold starts.

I never quite bought into this and figure it is just another old wives' tale.

I think most of the problems with silicone fluid start when guys try to change to silicone using the "bleed to flush" method. It doesn't work, but most people want to blame the material rather than admit that their process was flawed.

Duke

[Everett Ogilvie]

Re: silicone brake fluid

Agree with you both - as reported before, several of us who live at high altitude and drive at higher altitude in the mountains have never had problems with silicone fluid.

[Joe L.]

Re: silicone brake fluid

Everett-----

Yes, as a mater of fact, your experiences, as previously reported, are one of the "underpinnings" of my belief that the high altitude braking problems sometimes attributed to silicone brake fluid are really not connected to the silicone fluid, at all. If even ONE person were able to use silicone fluid at high altitude without problems, that means that there must be no fundamental problem with silicone fluid in regard to high altitude usage.

Other reasons for my belief include the fact that I've experienced the high altitude problem with BOTH DOT 5 silicone fluid AND DOT 3 and 4 glycol-based fluids. I know many other folks that have experienced it with glycol-fluids, too. Also, as I've said before, the "DOT" in "DOT-5" stands for Department of Transportation which is a government agency that sets standards for certain things automotive that relate to automotive SAFETY. I seriously doubt that any brake fluid which had a FUNDAMENTAL tendency to cause high altitude brake problems and/or brake loss would EVER be DOT-approved.