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Could those of you who used silicone brake fluid share their experience? Particularly, how does it affect hydraulic brake switch?
I've read a lot of cons and pros of using silicone and am pretty much set to go with this option in my 1950 Custom but still have to decide whether to keep my original hydraulic brake switch or to figure out how to replace it with a mechanical switch.
I am replacing the whole brake system - MC, wheel cylinders, all lines and hoses. My decision to go with silicone is motivated partially by all that heavy rust on the frame around MC that I had to clean and mostly by witnessing how just a single unseen drop of DOT3 left unattended overnight on my frame ate the paint all the way to the bare metal. And I just had this frame painted about two months ago... Bummer... 
Your opinion/advise is greatly appreciated.
Thanks,
- Igor.
Igor...I have owned my '55 Firedome since the early '80's. Sometime in the '80's, a mechanically gifted WPC Club member and friend assisted me rebuilding the wheel and master cylinders, replacing all brake hoses, shoes and questionable brake lines. Silicone brake fluid was all the rage at the time so we decided to flush the system and refill with silicone. I have never regretted that decision some ~25 years and 18,000 miles later. I've not had to open the system other than occasionally top off the master cylinder with silicone fluid and the pedal remains hard (no power brakes) and the braking straight. I regularly mechanically adjust the brakes and occasionally inspect the linings.
To your point, I've had to occasionally replace a brake light switch and have replaced them each time with an NOS switch. This occasional switch failure is a small price to pay for excellent brake system life with silicone.
Mark
Mark, thank you for your reply. That's an excellent point - I'm going to get myself a couple of extra switches.
I have used it in all of my vehicles for at least 20 years with no problems...including my 55 Sportsman and 32 Ford Roadster with disc brakes. The reason is to prevent internal and external rusting of the brake system...
I have used DOT 5 in my 39 desoto since 1987.
I have not had any issues.
In a prior post someone stated they use it to prevent rust onthe external parts inthe brake system.
Since brake fluid is only in the inside of the brake line how are you preventing rust onthe outside of the braking system?
Are you coating the line with the DOT5 but this will wash off when you drive the car in the rain.
Please explain?
Rich Hartung
desoto1939@aol.com
I have a 53 and have been using DOT 4 which is just a better DOT 3. I do not like its potential for eating up paint. I have thought about changing to DOT 5 silicone. What is the system flushed with? DOT 5 or is there something better to remove the DOT 3 or 4?
Paul,
Opinions on how to switch from Dot 3/4 to Dot 5 are ranging from flushing lines with denatured alcohol, blowing with compressed air and replacing all rubber seals and hoses to simply pushing out old fluid with Dot 5.
In my case I've replaced the whole system (new cylinders lines and hoses) so I'll just fill it up with Dot 5.
Here is a quote from http://www.imperialclub.com/Repair/Brakes/brakefluid.htm :
"I have converted about 15 cars to silicone fluid over the years, with generally good results. I disagree with the posting that said it is OK to just flush and replace the DOT-3 with DOT-5 though. The DOT -3 and DOT-4 fluids are alcohol based, and as such tend to expand rubber products. If you simply replace the fluid with DOT-5 (silicone) fluid, you are very likely to get some leaks from the shrinkage of the rubber parts back toward their unexpanded state. Possibly if the parts are nearly brand new you can get away with this, but I have found the only foolproof way to do it is to replace all seals and hoses, plus the brake light switch if hydraulically operated. I blow the lines dry with air and make sure all the old stuff is out of the system, then rebuild with all new rubber parts."
...In a prior post someone stated they use it to prevent rust on the external parts in the brake system.
Since brake fluid is only in the inside of the brake line how are you preventing rust on the outside of the braking system?...
Rich,
When there is even a smallest leak in a brake system, over time brake fluid will eat up paint and coatings on surrounding surfaces, making them susceptible to corrosion. Silicon fluid, on the other hand, will not destroy paint or coatings, thus less chances for the rust.
Since you already using Dot 5 - there is nothing to worry about 
- Igor.
P.S. Just adding a couple of before/after pictures - first one shows what kind of damage even a tiniest leak can cause over time (there where no visible drippings under the car and brakes were firm).
