C2 ('63) Brake System dilemma!

[Gary Cederman]

[Duke W.]

Re: C2 ('63) Brake System dilemma!

1. Silicone fluid apparently has a lower bulk modulus than glycol fluid, but I don't think this is going to make a material difference in brake pedal travel.

2. Silicone fluid has a higher boiling point than glycol, so this statement makes no sense.

3. Normal brake fluid does not "swell" rubber parts, but any kind of petroleum product conatamination will, which will likely lead to brake failure.

If you really trust these guys to do the mechanical work properly, just disassemble and clean all the parts in alcohol and reassemble it with silicone fluid, but I'd suggest you look for another vendor who will do it your way.

My hunch is that these guys just don't want to assemble the cylinder with silicone fluid, so they are giving you a bunch of BS as to why you shouldn't use it.

You raise an interesting issue about converting from DOT 5 to DOT 3/4. To convert to DOT 5 the system must be thoroughly flushed with a solvent to remove all traces of DOT 3/4, and the proper solvent in denatured alcohol. I don't know what solvent would be effective at flushing DOT 5 out of the system. Doens anyone know?

Duke

[Mike McKown]

Re: C2 ('63) Brake System dilemma!

Gary:

At this point, I don't see where you have a lot to lose by sticking with the Dot 5 on the rebuilt cylinder. If you run the Dot 5 and decide it's not for you and wish to change it, it is a simple matter to take the snap ring out of the bore of the MC and pull the guts out and clean it. It would be a small part of the overall flush job. What's required on the flush is up for debate. Some on this board tell you that all you have to do is install the changeover fluid and bleed until it "looks" flushed. On the other extreme, there are a few that insist that every last speck of the "other" fluid be removed. Which way is correct? I don't have a clue. I suspect many others on this board are in the same boat. I have silicone fluid in three cars. One is four wheel drum ('63 Vette), four wheel disc ('65 Vette) and disc/drum ('70 Nova). I like it for the reason you suggest. Will not attack paint!

As far as the warning from the rebuilder about insufficient pedal travel in older systems (or whatever the warning was), consider this: I haven't seen anyone in all the posts on this subject say anything about running out of brake pedal with the silicone fluid.

On swelling the seals: on the four wheel disc car mentioned above, I put all four calipers on it from Vette Brakes in I believe 1975. They were still on there until last Summer when I had to replace the front ones because the seals were leaking. The back two are still good and do not leak.

I defer to those with greater and higher knowledge.

[Mike McKown]

Serious question

Duke:

Maybe you can help a lot of us understand the necessity of totally purging the "other" fluid out of the system? This is not like mixing oil and water. This is two fluids that will accomplish the same task to a more or less degree. If there is a small amount of contamination left in the system from the "other" fluid, what does it really matter?

Would this not be analogous to draining synthetic oil out of your engine and putting in fresh regular oil without totally rinsing your crankcase?

Mike

[Gary Cederman]

Re: C2 ('63) Brake System dilemma!

Duke and Mike,

Thank you very much for your inputs.

Mike, I agree with your point that I really don't have much to lose at this stage if I stay with DOT-5.

I guess my biggest concern of going with DOT-3/4, is how do I flush out the DOT-5? As with other applications where silicon is involved, it is a very difficult item to clean off of the material that it is on.

Anybody else have any suggestions?

Thanks,

Gary

[Duke W.]

Re: Serious question

Actually, DOT 5 silicone and glycol fluid are LIKE oil and water. First, they do not mix, so it's impossible to purge all glycol fluid out by bleeding through silicone fluid. Since glycol fluid has a much lower specific gravity it will tend to migrate to high points in the system and remain trapped, and the moisture it contains will corrode the system locally, so you lose the corrosion protection of silicone.

I don't know if there is any chemical compatibility problem. Maybe not because silicone is relatively inert, but the physically incompatibilities of the two are sufficiently different to require special care that they not be mixed.

There is lots of anecdotal evidence that mixing them causes problems, but I don't understand the detailed cause and effect issues. Those who start from scratch with a clean and dry system and assemble all the hydraulic components with silicone fluid and then properly fill and bleed the system with silicone fluid rarely have problems. That's why I only recommend switching to silicone by starting from ground zero. A frame off restoration is a good time to do this since most frame-up restos include a complete ground up overhaul of the brake system. This can also be done on the car, but if you don't want to rebuild everything, assemble with silicone fluid, and thoroughly flush and dry all the brake pipes my recommendation is to stick with glycol and flush the system periodically to purge the absorbed moisture.

Duke

[Joe L.]

Re: C2 ('63) Brake System dilemma!

Gary-----

Please red my comments regarding DOT-5 which are on the "Break [sic] Fluid" thread further down the thread list. I'll add the following:

1) If DOT-5 silicone fluid were incompatible with seals and rubber parts commonly used for brake systems, then the product would not be DOT-approved;

2) There are too many folks who have used DOT-5 silicone fluid successfully for many years to believe that there is an inherent problem with its use. For all practical purposes, it's "tried and true". Most problems which some folks have attributed to the fluid are caused by other factors not related to the fluid type;

3) You should NEVER rebuild a master cylinder which has even the slightest pitting or scoring of the master cylinder bore. The pressures developed in a brake system are too high to withstand such cylinder wall imperfections

[Mike McKown]

Your point is taken Duke

Since I posed this question, I did a quick search and found that glycol and silicone fluids are in fact like oil and water to some extent.

If I can believe what I read:

Silicone fluid contain additives which lubricate the moving rubber parts. It is also dyed purple. When mixed with glycol fluid, the glycol will pull the additives and the dye out of the silicone and will create a sludge which will settle to the bottom of your brake system. It will also cause the silicone brake fluid to change color to amber brown.

This research paper was writtten by the Norwegian Military doing a study on military vehicle brake failures. It seems the motor pool was freely inter-mixing the glycol and silicone fluids in LARGE quantities.

Mike

PS The paper did not state how to flush the silicone system to remove contaminants.

[Duke W.]

Re: Your point is taken Duke

Great information, Mike! I wasn't aware of the additive incompatibility issues or the sludge formation, but this sounds like some decent science to support the anecdotal evidence that suggests mixing glycol and silicone brake fluids is a recipe for trouble.

Where the heck did you find this paper written by the Norwegian military??? If you found it on the Web, can you post the link?

Duke

[Gary Cederman]

[Wayne K.]

Re: Your point is taken Duke

Mike,

I've also been told that DOT-5 also will turn brown with age in a working system.

[Mike McKown]

Re: Your point is taken Duke

Wayne:

This report also addressed the fluid turning brown with age. I believe it said this happens but has no adverse effect on the fluid. I think it said, this was one reason the troops were inadvertantly adding glycol instead of the silicone.

Mike

[Terry M.]

Re: Your point is taken Duke *TL*

I too would like a reference to the Norwegian military information.

I will cite SAE (Society of Automotive Engineers) paper #780661 "Silicone Brake Fluids - Show us the Hardware!" from 1978. This paper was cited in a article in "The Corvette Restorer" from the early 80s. The entire paper is still available from SAE. They have a web site: www.SAE.org.

This paper will mention the sludge accumulation in a mixed system. "Included will be the results of well over two million miles of fleet testing which have demonstrated greatly improved performance and component life under a wide variety of adverse conditions." quoted from the paper abstract. You might find this paper interesting reading.

Yes, the purple dye in DOT 5 will disappear after years of service. At least that happened in my case, but perhaps the more current fluids have a different dye.

[Joe L.]

Re: C2 ('63) Brake System dilemma!

Gary-----

At this point, I think that it's impractical to remove the fluid. Clearing out the brake system of every drop of the silicone fluid means tearing down the whole system again and disassembling/cleaning everything.

Actually, I am not absolutely convinced that removing every trace of the glycol or silicone fluid is absolutely necessary. It is true, that when switching to silicone, some benefit of the fluid will be lost by having any glycol fluid left in the system. Water will then "hide" in the glycol fluid and cause corrosion wherever it "resides". There's less of a problem, in this regard, when switching from silicone to glycol since nothing will "reside" in any remaining "drops" of the silicone fluid which will cause any problem.

Although the silicone fluid and the glycol fluid are immiscible and insoluble in each other, both are liquids which are, for all practical purposes, incompressible. Inasmuch as they are immiscible and insoluble, they cannot "react" with one another to form some sort of reaction product which might be detrimental to the brake system. So, personally, I really don't see how they can cause a problem if both types of fluid are in the same system.

Nothwithstanding the above, I'm always uncomfortable about mixing things like this and I would want to remove every trace of one type of fluid before switching to another. I think it's likely irrational, but I do a lot of things that are irrational. Like, for instance, I would never mix 2 different brands of oil in an engine, although it's perfectly acceptable to do so as long as the oils are API-rated (which is just about all of the automotive oil on the market today).

[Joe L.]

Re: Your point is taken Duke

Mike, et al------

A few comments:

1) If silicone-based brake fluid and glycol ester-based brake fluid are immiscible and insoluble in each other (which they definitely are), then I do not see how they could react with one another and form any sort of reaction product (i.e. "sludge", "varnish", etc.). The only way that it could possibly happen would be if the silicone fluid "additives" were also soluble in the glycol fluid. Even then, I would think that the chances of them being "pulled out" would be very small and the most that could happen would be the loss of whatever additives from the silicon fluid . This would be especially true if only very small quantities of glycol fluid remained in the system converted to silicone. The amount of "additives" that could be "transferred" from the silicon fluid to the glycol would be deminimus;

2) the dye used for silicone fluid is very degradable. Even stored in its original container it will change from purple to yellow. I don't know what instigates the change, but it's certainly not heat or an acidity change.