MGA Forum

When my car comes back from the paint shop with a bright shiny (and expensive) new coat of paint, I intend to switch over to silicone brake fluid. Let's not get off topic into the classic silicone or not discussion. I'm interested in hearing folks experience with the best way to clean the old fluid out of the brake lines before switching over.

well i installed all new lines so i didnt have to clean any thing out but i cleaned the pressure bleeder with denatured alcohol.

i think thats the only way do to it.

Flush your system with brake cleaner - worked for me on two cars so far. You will need to replace all the rubber components in the system before using silicone fluid though.

Bob's idea is probably a good idea!

On our BGT rebuild we put all new hoses and rebuilt the master cylinder. But before we did that we had drained the old fluid out, then blew air through the system.

I was amazed at how little brake fluid the system uses.

On our current A project we have put all new pipes and will run some new fluid through it all.

I would recommend changing ALL rubber parts before switching. That's all, but you will get different answers on that! I changed hoses and seals, so master, slaves and callipers were cleaned out in the process and lubricated with silicone fluid. I will probably be shot down now, but I then just flushed through with silicone fluid using an eezibleed. I have done the same on three cars now. The first in the 1980's and my current MGA in 2006. In about 2010 there was a discussion on silicone fluid on the other forum and it was mentioned that someone had horrible black stuff in their silicone fluid when bleeding their brakes. I went out and ran 1/4 pint through each corner (again using the eezibleed) and the fluid was crystal clear. I haven't touched it since. On a rebuild I would change all the brake lines as a matter of course and so cleaning doesn't apply. The other thing I do is reuse silicon fluid. If it gets contaminated I just let it settle and then decant the the clear fluid off the top, leaving any old fluid, water or bits at the bottom. I did once pour it through a coffee filter, but it took a while and I couldn't see any particles on the paper, so never bothered since.

Neil,

The reason I recommend using brake cleaner to clean the lines versus flushing with silicone is cost. Silicone fluid here in the States is ridiculously high in price compared to Dot 3/4 so I find it more cost effective to use something cheaper...and the silicone fluid you flushed with shouldn't be re-used in the system (at least I wouldn't).

Gene

Andy, I used denatured alcohol to purge my system of silicone fluid when I changed over to DOT 3/4.

Just because you are planning to use silicone, don't get lazy and not flush the fluid every year or so. My silicone brake fluid developed jellyfish like deposits at the bottom of the master cylinder, and perhaps elsewhere. I believe that was an emulsification of H2O and the silicone fluid. Also parts of the master cylinder became rusty and the master cylinder and to a much lesser degree the clutch slave cylinder developed rust deposits.

I think all of these conditions were because the silicone brake fluid doesn't absorb water. Whatever water gets into the system just sits there.

I'm not saying don't use it. Instead, I'm saying don't ignore it.

I switched back to DOT 3/4 because I was looking for a firmer, more responsive pedal. But I drive like a maniac - well, at least I'd like to think that I drive like a maniac. I don't think you would ever notice any pedal difference on the street.



Edited 1 time(s). Last edit at 2015-03-01 02:54 PM by Blueosprey90.

Hey Andy,
I switched to silicone fluid 5 years ago and have been very happy with it. When I changed over my system it had been emptied when the slave cylinder boot split allowing the DOT 4 fluid to leak out. After getting the car home, I fixed the slave cylinder, filled the system with denatured alcohol, flushed the system, let the system dry out and then flushed the system with DOT 5 silicone fluid, then filled it up and bled the system. I flush the system every 2 years to remove any water and dirt. I know many have reported that silicone fluid will eat up rubber parts and cause leaks but I have not experienced this even though I did not change all of the rubber parts prior to making the change to silicone fluid. Hope this info helps.
Ron

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Clothes make the man. Naked people have little or no influence on society. Mark Twain

Many thanks for all the replies. I had already planned to rebuild the master, rebuild or replace clutch and wheel slaves, and replace the rubber hoses. Wasn't sure about how t clean out the brake lines though. Replacing them seems wasteful and expensive. Sounds like a flush through with denatured alcohol and a blast or two of compressed air should do the trick.

As a matter of interest, What pressure does the system work at with brake fluid ? and at what stage do you use air to clean the system, at rebuild, or when it's complete ?

Mark.

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We will talk a little later when we are older.

This is an extract from an MGCC Safety Fast article on the fluid back in November 1999. I have a feeling it was originally produced by a US MG Club.

........"I have found that the best way to switch over is with a complete system overhaul. The brake lines should be flushed with acetone which dissolves the glycol gummy residues and removes any trapped moisture. The lines should be dried by blowing with air (ethyl alcohol can also be used, it is not as flammable and won't injure paint). All flexible lines and seals should be replaced so that all rubber that has been exposed to the glycol is removed."..........

Bearing the thread originator's request in mind and avoiding the pro/anti silicon debate, I feel the comment above about brake pedal movement needs a response. The same article I have quoted also notes that although silicon is 3 times more compressible than other fluids, it is still minuscule and adds only 0.1mm travel to the brake pedal.

Steve