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MG MGB Technical - What to use to flush out silicone?

Hello-

My clutch master went DOA so I'm replacing it and the slave also. The PO had silicone in the system but I want to return to LMA. What solvent/chemical can I use to flush out the silicone from the line that won't damage the rubber flex hose at the slave cylinder?

Thanks for any suggestions-
Sam Sullivan
Sam

I used denatured alcohol when I switched my brakes back to Castrol LMA from silicone. I
flushed the system three times. I installed new seal kits and pistons in the calipers,
disassembled the rear brake cylinders and cleaned them. I didn't take the master cylinder
apart and so far no problems. I reworked the calipers because the pistons were bad, not
because I was changing fluid. I prefer the pedal feel I get with Castrol LMA. FWIW, Clifton
CLifton Gordon

Sam - Brake Kleen works well and comes in a pressurized can which makes cleaning the brake lines a bit easier to deal with. Good luck - Dave
David DuBois

If you use alchocol you risk drying out all the seals....................
Bob

Sam-
Everything that I've ever tried to use to remove silicone brake fluid has always failed, including alcohol and CRC Brake Kleen (which is alcohol-based). However, I just had a brainstorm. If you try to paint over silicone the result is fisheyes in the finish. Perhaps the local automotive paint store knows of something formulated to remove it in preparation for painting. Whatever will remove that nasty stuff will probably ruin your brake hoses, but it's worth checking out.
Steve S.

Steve: Fisheyes, yes I tried to paint the pedal box after using a chemical stripper and wiping
down with a paint thinner. I stripped it again and still had fisheyes, so I painted my spare and
used it. I didn't say in my earlier post but I did replace the flex brake hoses. It's been about four
months now and so far ok, but I'm holding my breath on the master cylinder. Clifton
Clifton Gordon

With anything you use there will probably be a slight surface coating of the silicone fluid, but since you are not painting the inside of the brake lines, I doubt that it will be of any consequence. The two fluids will not mix, but they will coexist together with no problems. The only reason to get all of the old fluid out when going from DOT 4 to silicone is that any DOT 4 left in the system will continue to draw moisture and cause corosion. Going the other way around should not be a problem if there is a surface coating of the silicone left in.
Cheers - Dave
David DuBois

Thanks all for your comments. Maybe I should flush out the line with paint!

Sam
Sam

You know, such an insight (to possibly use silicone removers used for painting) was espoused sometime back on this very BBS. If you go rummaging in the archives, you can probably find the procedure outlined as a possible way of using this to your advantage.
Bob Muenchausen

What would be the benefit to removing the silicone fluid? My understanding(limited as it is) is that moisture in the break lines is disasterous in the long run and silicone eliminates that problem. Do the new versions of non-silicone fluids resist moisture absorbtion?
Ed

Ed-
It's commonly known that silicone-based brake fluid doesn't absorb water like the petroleum-based brake fluids do. However, this presents a problem that many fail to forsee. Whatever water that may enter through the vented master cylinder and condense inside the system clumps together as a result of capillary action and whereever it may eventually settle due to its higher specific gravity in the metal lines, calipers, or slave cylinders, it will cause rust. In addition, because the water is localized in one spot, it can freeze in cold weater and block the line if there's enough of it. This is admittedly rare. On the other hand, petroleum-based brake fluids absorb water which then disperses evenly throughout the brake fluid. Petroleum-based brake fluid will provide a limited degree of protection from rust until the water content gets too high. This is why all brake fluids should be changed annually. If your brake fluid has turned brown, it's loaded with water and its definitely time to change it.
Steve S.

Steve S. - I believe that the issue of water entering the system through the cap vent is a red harring. I have had silicone fluid in the brake system of our TD for the past 20 years and there is absolutely no water or corrosion in the system, even though the fluid has not been changed in the whole time. The master cylinder and filler cap on the TD is underneath the car below the driver's feet, where it catches all the road spray. Our car is driven at least once weekly (usually more often) in the very wet and soggy Western Washington State. I have not had a problem with oru MGB getting any water in the braking system, but it"s master cylinder is located where one wouldn't normally get water on it (unless one is into fording rivers with their MGB. Based of the above, I have always considered the problem of getting water in the system through the cap vent to be an old wife's tale (question is, whose old wife? ; ) ). Cheers - Dave
David DuBois

Ed, not everyone likes the pedal feel of Silicone fluids. From what I hear and read there is even some debate as to which brand of the stuff provides a stiff pedal like the glycol fluids seem to do.

However, Silicone fluid has become such an icon, that it's own mythologies are seldom questioned.

The archives for most of the various MG models delved into on this BBS on this subject should give you a notion as to the issues on both sides that people agree and disagree with, and also some of the craziness that has come along for the ride over the years.

Silicone fluids did not emerge fully developed and they too have undergone a bit of improvement as some of the early silicone fluid's shortcomings were admitted and the fluid reengineered.
Bob Muenchausen

All this talk of soft pedals with silicon is baffling to me. I have used silicon in my A for 14 years, and when anyone drives it, the first thing they say is how hard the brake pedal is.

And as to water getting into the brake system through the pinhole on the M/C cap, and collecting and freezing it's absolutely "worst case" engineering. Has anyone ever actually seen this? Don't you think it might just be noticed by a driver who has no brakes. And just how much ice is required to completely cause a brake system to cease functioning?

It's far more dangerous and common that people leave their brake fluid in their car for years without changing it, or any seals in the brake cylinders. The cylinders always go because of rust, starting slowly, then deteriorating rapidly. With the Si fluid, there is no moisture absorbtion, therefore no internal rust.
dominic clancy

Dominic:
You raise some good points.

As for hard and soft pedals, my own luck and that of those around me has had more to do with how well a system has been bled than the nature of the fluid. My understanding is that both have to meet certain minimum standards on many engineering fronts and that compressibility is just one of them.

As for corrosion in the system, I think that is properly a maintenance issue, more appropriately laid at my feet as the owner/operator/mechanic for my car than at the inherent degree of hydroscopic action of most modern glycol fluids. I find that if I flush my systems at least every two years (better is yearly), I can run just about as long on glycol as other people do on silicone before some truly mechanical problem plays its hand. The archives are full of discussion of lubricity, and other factors between these two fluids, but over the years now, I am finding that it is far more a matter of maintenance and observation of change in the hydraulic system that keeps either of these fluids doing their job than it is the "inherent superiority" of either. FWIW


Bob Muenchausen

This thread was discussed between 15/07/2002 and 17/07/2002

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