I just rebuilt my complete brake system, then used the DOT 5 silicone brake fluid. I am writing this due to all of the negative information that is out there on DOT 5 fluid.

I have done much research on this topic and personally contemplated which fluid to use over last few months.

I have always hated conventional brake fluid,Hygroscopic, eats paint, no shelf life when open and completely corrodes the system it was designed for if you do not flush often.Plus the rust on the outside off the master cylinder.

This all started because my Rt front caliper was starting to seize, the master cylinder began to leak ( and ate the paint off my frame) and my old brakes lines were in great shape but were just not cosmetically acceptable.

I started by vacuuming out all of the old fluid in the lines and master cylinder to keep brake fluid from getting all over the place wile removing.

I then flushed the entire system out thoroughly with alcohol and blew everything out with air. Removed all of the lines,calipers,wheel cylinders etc.

I took the calipers and wheel cylinders apart and cleaned then rebuilt using silicone. The calipers had quite a bit of rust in them but the pistons were very dirty but pit free. I wanted to rebuild the combination valve but I could not find all of the seals,so that got another real good flush. Replaced the MC with a Fenco looked like a quality new unit, I didn't want to deal with a rebuild that might possibly leak down.

I replaced all of the brake lines with new stainless from Classic Tube, they are about a mile from us and there lines were all bent well, fittings were color coded just like the originals, not to mention extremely easy to work with.

Bench bled the MC using the new procedure of plugging the line ports off, bleed till no bubbles and until the plunger gets rock hard to push (worked very well and no mess, also when your done you know if MC is good) then installed it and filled. I used the gravity bleeding method and worked well, I usually do this because I never have a helper. I did have to re-bleed the MC, first go the pedal was a little soft, I think due to the system being new with no fluid.

I must say this went very well and I don't think I will ever use conventional fluid again in a vehicle like this, I think the pros especially for a classic car far outweigh any of the disadvantages. The pedal is rock hard and everybody told me it would be very spongy, my guess is they probably didn't get all of the air out or the fluid was aerated as silicone can get if shaken. I think the silicone will protect all of the internals from corrosion and doubt I will need to flush for years to come. After reading all of the complaints about silicone, I saw very little info about current problems with conventional fluid and how that can damage a system if not changed frequently.

I do though think you should be careful not get the silicone on parts you want to paint in the future,it might very difficult to fully clean the part to paint

Just thought this info might helpful to others thinking about the change.

 

What are the pros & cons of running the DOT 5 fluid?

 

Dot 5 silicone pros; Will not attack paintwork if spilled. Is not hygroscopic (it doesn't absorb water).
Cons; Cost. Not every parts store has it on the shelf. Every trace of old brake fluid must be removed from the hydraulic system before use.

Regular brake fluid: See silicone fluid pros & cons but in reverse.

Roger.

 

Here is one of the articles I read on the subject. It is very informative.


Quote:

Looking at the data we have compiled, it is apparent that the drop in boiling point of DOT 3 brake fluid over time due to water contamination means you must consider changing the fluid every 12 months, regardless of how much you drive. If you live in a dry, arid climate, you can extend that somewhat. Conversely, if you live where it is wet and humid, the 12-month interval might be too long. If you use a DOT 4 fluid, be aware that it actually absorbs water faster than DOT 3 fluids, but the reduction in boiling point is less. With DOT 4, consider changing the fluid every 18 to 24 months. These are conservative recommendations, but they do not guarantee that you will eliminate the chance of a brake system vapor-lock related failure because they do not take into account the actual amount of water contamination in your brake system. To find out, you will need to physically test samples of your brake fluid.
Silicone Fluids
When compared to glycol fluids, silicone has some distinct advantages. They are very stable over wide temperature ranges, and they resist physical and chemical change under severe heat, cold, sheer, oxidation, and other operational conditions that will break down other fluids. They are inert, non-corrosive, non-toxic, and have low volatility. Silicone fluids also have the lowest viscosity change with temperature of almost any hydraulic fluid.

Water Absorption

Unlike glycol-based fluids, silicone fluids are not hygroscopic. Silicone brake fluid will absorb a tiny amount of moisture and then absorb no more. Because water will not mix with silicone fluid, any water that gets into the system will tend to pool in the lowest parts of the system. This resistance to water absorption is a critical difference that makes silicone fluids attractive for cars that are driven seasonally, which makes the longer term issues of corrosion more important than they are with a daily driver.

Boiling Point

Silicone fluids have very high dry boiling points – generally around 600° F. The wet boiling point is a little confusing; how can a fluid that does not absorb water have a “wet” boiling point? A sample of humidified silicone brake fluid will actually have the same boiling point as the “dry” sample – in the case of the Cartel DOT 5 fluid, 600° F. Since silicone will “float on top of the water,” the tiny amount of water logically will in time work is way down to the lowest points in the system. In theory, if that low spot is the caliper, the water can boil at 212° F, well below the dry or the wet boiling point.

Bleeding Water from Systems with Silicone Fluid

Because even a tiny amount of water will lead to corrosion, and water in a caliper or wheel cylinder can boil at relatively low temperatures, it is advisable to bleed the system every six to 12 months to eliminate the water.

Hazard to Paint

Unlike glycol fluids, silicone fluids do not damage paint. This is of particular importance in regard to show cars where a spill or leak of glycol fluid can have seriously ugly results. A newly rebuilt and scrupulously clean brake system filled with silicone fluid should outlast a system filled with glycol fluid by several times.

At this point, the silicone fluids have what appears to be an obvious advantage over glycol based fluids. Given all the trouble caused by water contamination of glycol based brake fluid, silicone fluid has some appeal. However there are some drawbacks, and we need to understand those before we start making choices.
Drawbacks of Using Silicone Brake Fluid
Air Solubility

Silicone fluid will absorb more air because there is more “room” between the molecules that make up the fluid. The term “dissolved air” (air absorbed from the atmosphere) should not be confused with the term “entrapped” or “free air” since their effects on brake system performance can be entirely different. Air that has been absorbed from the atmosphere does not result in an increase in fluid or system volume, whereas entrapped air or free air does occupy system volume and can be easily compressed when force is applied to the system.

Compressibility

Because of the dissolved air, silicone fluids are up to three times more compressible than glycol based fluids. This can contribute to a slightly spongy feeling brake pedal, particularly near the higher end of their temperature range but well below the dry boiling point. While this is of absolutely no consequence for normal street use, this is why silicone fluids are not used in race cars. A spongy pedal makes it difficult to modulate the brake pressure under racing conditions.

Bleeding Air From Systems with Silicone Fluid

Silicone fluids have a higher viscosity, which combined with a greater tendency to absorb air leads to slow rates of fill and retention of free air entrapped during filling, which makes bleeding the system difficult. Because air bubbles do not easily dissipate in silicone brake fluid, special care must be used to prevent them from forming during pouring and bleeding operations. The best way to bleed a silicone fluid system is with a professional brake bleeder with a sealed fluid reservoir separated from an air chamber by a rubber diaphragm. The air pressure forces the fluid from the chamber into the reservoir and through the lines to the individual bleed screws. This is very effective, but few individuals will find them practical because of the large amounts of brake fluid they use. There are two vacuum bleeders that will work too. These are the “Professional Vacuum Brake Bleeder” (Moss #386-225), and the “Vacuum Brake Bleeder” kit (Moss # 056-671) will also work. If you do not have either of those, bleed the system with slow even pedal strokes. Avoid "pumping" the pedal, which will introduce air bubbles into the system. It may be necessary to bleed the system again in a day or so if there were any air bubbles that wouldn't bleed out the first time. Be aware that air in solution in silicone fluid will form bubbles if the atmospheric pressure drops, as it does when you go up quite a bit in elevation. This will result in a spongy pedal that will persist until the air is bled out of the system.

What About the Stories of Silicone Brake Fluid Causing Seals to swell?

These stories abound on the internet, but I have not actually spoken to the person it happened to, so I cannot comment on the actual incident that started the story. We do know that it is very, very unlikely that a brake fluid meeting FMVS 116 would do that. The testing is designed to make that sort of thing impossible. I can tell you that the literature is full of reference to the grotesquely swollen and gooey seals that you get if the brake system is contaminated with petroleum based oils or solvents. It does not take much of this kind of contamination to ruin all of the seals in a system. The contamination can usually be traced to the use of improper cleaners, rags contaminated with motor oil or grease, or handling the seal with hands that have petroleum based contaminants on them. We have tried to duplicate these reported problems by soaking brake cups in DOT 5 fluid, but we have never found a problem. However, these stories have a life of their own and it is doubtful that they will ever go away. It is perhaps a modern version of the traditional British natural rubber brake seal warning about using “the wrong fluid.”

Converting from Glycol to Silicone Fluid

If you do decide to convert to silicone fluid, it should be done as part of a total brake system overhaul, with freshly rebuilt or new calipers, wheel cylinders and master cylinder. Silicone fluid should not be added to a system that contains even small amounts of glycol fluid or contaminants. Merely bleeding the system is not enough, as there will be pockets of old fluid and sludge that will not bleed out. Silicone fluid tends to concentrate any residual glycol fluid, moisture and sludge into slugs instead of allowing their dispersal throughout the fluid, as does glycol fluid. This can lead to relatively severe but localized problems, rather than the more general system deterioration experienced with old moisture-laden glycol fluids. This may be a factor in reports of leakage when silicone fluid replaces glycol fluid in non-rebuilt systems. A "new" system full of silicone fluid will require very little maintenance for years

Hope this helps

 

72w442:
Wow! Thanks for sharing so much info. I'm rebuilding my entire brake system so the switch to silicon fluid is something I'm considering. The article mentions using silicon fluid after a complete brake system overhaul; won't there be residual amounts of DOT 3 fluid in new calipers and wheel cylinders because of manufacturer assembly and testing? What's the best way to flush these components?

Rodney

 

Rodney,

I had the same question for my new MC as I really didn't want to dismantle.

I just flushed it with alcohol. The assembly lube is more like a waxy oil than brake fluid.

All of my old components had this stuff still in them even after years of use. I don't think they assemble them with brake fluid due to the ability of brake fluid to absorb moisture, they would probably start to corrode before you installed them.

But I would guess the best way would be to disassemble and clean and put back together using silicone, that is what I did with everything except the MC and combo valve.

Your frame looks great, I regret not doing a real frame off on my car.

Good luck

 

72w442:
Thanks for the advice and the compliment.