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Installed new power disc brake system on wife's 55. New lines, everything. I want to use silicon brake fluid in the system, but the kit says "silicon fluid NOT recommened" Anyone know why? What are the pro's and con's? Thanks....David
 

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Silicone brake fluid in power brake systems are not recommended because if the engine vacuum pulls fluid eventually (because of worn seals) it will turn into a grit like sand and can harm your engine.
That seems weird, but there are even more reasons not to use it. Check out this site:
http://adlersantiqueautos.com/articles/brake1.html

That being said, on a manual brand new stainless system on my vette, it has worked flawlessly. I cant say i have many miles on it though :)
 

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I found this:
SILICONE BASED FLUID
Fluids containing Silicone are generally used in military type vehicles and because Silicone based fluids will not damage painted surfaces they are also somewhat common in show cars.

Silicone-based fluids are regarded as DOT 5 fluids. They are highly compressible and can give the driver a feeling of a spongy pedal. The higher the brake system temperature the more the compressibility of the fluid and this increases the feeling of a spongy pedal.

Silicone based fluids are non-hydroscopic meaning that they will not absorb or mix with water. When water is present in the brake system it will create a water/fluid/water/fluid situation. Because water boils at approximately 212º F, the ability of the brake system to operate correctly decreases, and the steam created from boiling water adds air to the system. It is important to remember that water may be present in any brake system. Therefore silicone brake fluid lacks the ability to deal with moisture and will dramatically decrease a brake systems performance.

POLYGLYCOL ETHER BASED FLUIDS
Fluids containing Poly glycol ethers are regarded as DOT 3, 4, and DOT 5.1. These type fluids are hydroscopic meaning they have an ability to mix with water and still perform adequately. However, water will drastically reduce the boiling point of fluid. In a passenger car this is not an issue. In a racecar it is a major issue because as the boiling point decreases the performance ability of the fluid also decreases.

Poly glycol type fluids are 2 times less compressible than silicone type fluids, even when heated. Less compressibility of brake fluid will increase pedal feel. Changing fluid on a regular basis will greatly increase the performance of the brake system.

FLUID SPECIFICATIONS All brake fluids must meet federal standard #116. Under this standard is three Department of Transportation (DOT) minimal specifications for brake fluid. They are DOT 3, DOT 4, and DOT 5.1 (for fluids based with Polyalkylene Glycol Ether) and DOT 5 (for Silicone based fluids).
 

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I found this:
SILICONE BASED FLUID
Fluids containing Silicone are generally used in military type vehicles and because Silicone based fluids will not damage painted surfaces they are also somewhat common in show cars.

Silicone-based fluids are regarded as DOT 5 fluids. They are highly compressible and can give the driver a feeling of a spongy pedal. The higher the brake system temperature the more the compressibility of the fluid and this increases the feeling of a spongy pedal.

Silicone based fluids are non-hydroscopic meaning that they will not absorb or mix with water. When water is present in the brake system it will create a water/fluid/water/fluid situation. Because water boils at approximately 212º F, the ability of the brake system to operate correctly decreases, and the steam created from boiling water adds air to the system. It is important to remember that water may be present in any brake system. Therefore silicone brake fluid lacks the ability to deal with moisture and will dramatically decrease a brake systems performance.

POLYGLYCOL ETHER BASED FLUIDS
Fluids containing Poly glycol ethers are regarded as DOT 3, 4, and DOT 5.1. These type fluids are hydroscopic meaning they have an ability to mix with water and still perform adequately. However, water will drastically reduce the boiling point of fluid. In a passenger car this is not an issue. In a racecar it is a major issue because as the boiling point decreases the performance ability of the fluid also decreases.

Poly glycol type fluids are 2 times less compressible than silicone type fluids, even when heated. Less compressibility of brake fluid will increase pedal feel. Changing fluid on a regular basis will greatly increase the performance of the brake system.

FLUID SPECIFICATIONS All brake fluids must meet federal standard #116. Under this standard is three Department of Transportation (DOT) minimal specifications for brake fluid. They are DOT 3, DOT 4, and DOT 5.1 (for fluids based with Polyalkylene Glycol Ether) and DOT 5 (for Silicone based fluids).
Hard for me to put much faith in this report since they use the word hydroscopic a few times.

That's not even a word

The word is hygroscopic

http://www.fouragesofsand.com/2011/...ence-between-hydroscopic-and-hygroscopic.html

Just sayin
 

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Because they used the wrong word, the whole thing must be bunk. That's a good thought.......One must have thought Hydro, meaning to do with water when writing the article.

Read up on DOT5 and see about the issues. What they said is readily the same on many different resources, regardless of hygroscopic vs hydroscopic.

Hygroscopic is a word, as it pertains to a hygroscope.....


hydroscope (ˈhaɪdrəˌskəʊp) [Click for IPA pronunciation guide]

— n
any instrument for making observations of underwater objects

hydroscopic

— adj

hydro'scopical

— adj

This is what makes this forum so entertaining. Scientists and teachers, have to love them.
 

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Nah, not at all.

I just would not discard the ideas in the article because someone used a wrong word. I have found very little use for DOT5 in street applications. The only thing positive I have heard is it is easy on the paint.

:shakehands:
 

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Cool
Did you look at the initial link i posted???
It seems like a great article.
As I said before I have silicone in my stainless brand new system and I actually forgot that we are also using it in my wifes little sports car.
Its been in there for a couple years and the brakes have never worked better.
The fact that it doesn't destroy paint is a great benefit for sure.
I want to see how it lasts long term. That will tell the tale.

Still I would never use it in a power brake system (hydroboost, maybe??)

As far as the article, if someone got paid to write that, someone deserves a refund!

JMHO

:shakehands:
 

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Ok, I came across this one. I didn't see hydroscopic in it anywhere. I did see there is now a DOT5.1, which I had never heard of. Below is a section of the article as it relates to DOT5. The entire article is here>>>
http://www.stoptech.com/technical-support/technical-white-papers/brake-fluid

The original DOT 5 fluid specification was expected to be fulfilled by silicone based (SSBF) composition. It was designed for use in applications where its resistance to water absorption (and therefore low corrosion) was desired - like in military equipment. It has also found use in antique cars because it does not dissolve paint finishes. With SSBF, unfortunately, these characteristics were only achieved by unacceptably high compressibility. As such, the DOT 5 grade SSBF is of little value to any conventional automotive or high performance application.

Subsequently there have been non-silicone based fluids developed that meet DOT 5 wet and dry boiling point specifications and viscosity requirements. They are referred to as DOT 5.1 grade fluids. As a special case they are listed here for completeness.

Please remember that the specifications are minimums and therefore the non-SSBF DOT 5 fluids do not offer the highest boiling points available. There are no DOT 5.1 brake fluids that exceed the dry and wet boiling points of the best of currently available DOT 4 racing brake formulas. They do meet the lower viscosity specifications, however.
 

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I'm sorry BelRay, I forgot to mention I did read the article you posted. It is informative. I think the only real advantage, it does not eat the paint. Be careful and don't spill the brake fluid, and if you do, clean it up. I lost paint on a fender once to antifreeze....what a mess that made.
 

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There are two clear choices here.

1. For the best brake performance, DOT 3 or 4 fluid, changed regularly, is the best way to go. You won't see a competitive race car with DOT 5. This is because of its compressibility and the inherent difficulty of bleeding DOT 5.
2. For a show car, trailer queen, or museum car that doesn't get driven much if at all, DOT 5 is probably the best choice because it's not hygroscopic, and it doesn't harm paint.

That leaves everything else in the middle. But I'll go with the DOT 3/4.

I don't think that hydroboost really has any bearing on what to choose. I've never heard of the weird problem described. I kind of discount it, because if your master cylinder leaks back into the booster interface area, you have problems no matter what brake fluid is used.

The other thing about this is that the DOT 5 is not compatible with DOT 3/4. Mixing will produce a gel. So the only logical time to put DOT5 in a system is when everything is new or rebuilt.
 

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Not trying to burst anyones bubble or argue with anyone when I put discs on my 57 in 1989 I had just painted the firewall so I went with silicone fluid I didnt have any problems bleeding it, have never had a spongy pedal, the car has sat for about 10 years now the brakes are still up there and work just fine, no leaks in the system and the paint below the master is still in good shape, Ive heard all the horror stories about the evils of silicone fluid but based on my experiences with it I dont agree with the critics
 

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OK science class:)
I just did an interesting mad scientist type experiment.
Well maybe more of a ******* experiment (no offense anyone)
The attached photo is the after effects of applying a torch to brake fluid.
This would be similar to what would occur if your power brake seals leaked and sucked the fluid in your engine. Of course there would be much more heat and pressure that I can't duplicate, and could conceivably make this worse.
The left corner is DOT 3 clean and still actually burning in this pic.
The right corner is DOT 5 silicone. It is a gritty, slimy pile of [email protected] that i would not want to shove down the throat of my engine.

Yes Rick it is true that if this happens, you have bigger issues. But will you know about it before your cylinders are sandblasted??

Still (and even more now) I would not recommend silicone brake fluid DOT 5 in a vacuum power brake system

Something to think about
 

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We've pretty much debunked the tale of the silicone fluid being the wrong fluid...
Cases in point:
33 Ford street rod 16yrs, and never an issue.
2 55 Chevies 5 and 15 yrs, ditto.
1960 Impy 5 yrs, ditto.
Numerous other hot rods over the last 15-20 yrs. Never an issue reported.
 

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If you want to waste and evening just Google Corvette Silicone Brake fluid. This conversation has been going on since the mid seventies. That being said, I rebuilt my 71 Corvette brakes in 1985 and used silicone brake fluid. I drive the car maybe 200 miles a year and the brakes are still preforming fine. Also, I have never noticed the spongy pedal associated with silicone fluid. In 1993 I rebuilt the brakes in my 62 Impala and added disc brakes. It has been driven quite a bit more and has gone through several changes, the last one about 6 years ago when I converted it to drop spindles and 13 inch rotors. Through these changes the rear brakes were checked but not replaced. It has regular brake fluid in it. It has had no brake problems either. If I was doing another C2 or C3 Corvette I may use silicone fluid but I don't really see much long term advantage. If you are worried about moisture build up in the system, just bleed the brakes every couple of years.
 
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