Silicone Brake fluid

I'm guilty of brake fluid benign neglect, and getting away with it.... I've kept an old '80 Olds Cutlass just because it has been a loyal family car for years and I like how it drives. . About 10 years ago I converted ONE part of the dual master cylinder to DOT 5, and never got around to doing the other half. Result; no problems!

excellent article
thanks for sharing

greg

Here is a link to a very good Brake Fluid Tech article below~

I know this is a very old forum thread~~ but I thought this article might be of some future interest.

www.mossmotors.com/SiteGraphics/ ... _long.html

To look at it another way, why is it that Harley is virtually alone among the manufacturers of wheeled vehicles in installing (or recommending) DOT 5?

We can all discuss Dot 3 And Dot 5 brake fluid until "the cows come home". Some are happy with one and others are happy with the other. It makes for interesting talk.

I do not want to tell anyone which to use. However, after brake cylinder rusting on my Auburn 30 years ago I switched to Dot 5. Since then my Cord, three Fords and my Willys all use Dot 5. We have put probably 60000 to 70000 miles spread among the cars with no brake problems. As said; Dot 5 is a little difficult to accomplish the initial bleeding.

I guess the Harley-Davidson engineers did not talk to the EIS engineer before H-D specified Dot 5 in all their motorcycles so they would not have moisture problems with their brakes.

I agree an old car owner can use whatever brake fluid they chose. I also agree they can disconnect the air bag..remove seat belts..disconnect emission devises or any other safety device they dislike. The danger comes when you recommend others follow your advise on defeating factory designed safety systems.

I contend the people who brag the most on the success of silicone brake fluid in older cars are those whose vehicles live a pampered life. The cars are in a climate controlled environment. They are driven only short distances in perfect weather. I contend those cars would probably do better if automatic transmission fluid was used in place of silicone brake fluid.

The danger of bragging on the merits of silicone fluid is it encourages use in vehicles that are not sheltered. Consider the guy from Galveston who drives his 1954 Chevy every day. The car is exposed to more moisture in a day than a pampered car may see in a lifetime. Silicone fluid does not control the moisture that WILL enter an open vented brake system. Ignoring a problem does not make it go away.

Department of Transportation regulations REQUIRE the brake fluid used in DOT 3 systems be hygroscopic. That quality above all others is what makes brake fluid brake fluid. Absorbing moisture is not a flaw of DOT 3 brake fluid...it is it's job.

The use of silicone fluid in older cars has a downside. That is especially the case in "non-pampered" driver grade cars. That is why the EIS Brake Corp. engineer told me "it was criminally liable" to recommend DOT 5 fluid in any application for which it was not designed.

Of course you can always buy a 1931-33 Auburn eight and forget about brake fluid altogether. :rolleyes:

Interestingly, Mike, in my book I give no specific recommendation. Just present what I believe to be the facts. As you say, I do not believe there is a "definitive" answer. Every owner will have to make his own decision.

I love this topic. you notice it has had 659 views. This subject has been argued for the last 20 years. Every person has their own experience and views, so if you think you will get a definitive answer, good luck. Silicon also has a tendency to leak more than Dot 3, but for what it's worth, I use it.
CORDially Mike

I'm with George. I know there are many Cord and Auburn owners who have used DOT 5 for years happily. Me, I could never get a really hard pedal with silicone. As far as I'm concerned the only advantage of DOT 5 is that its a lousy paint remover.

And Jim is 100% correct re: flushing either kind of fluid regularly.

I've already been paid for it so I don't get any more money if you buy it, but I suggest you look into my recent book "How To Keep Your Collector Car Alive". Especially the chapter called "The Least Changed Fluid". (You'll recognize a few photos of my Cord in there too

To quote a brake engineer from EIS Corporation..."using silicone fluid in a system for which it was not designed is criminally liable." Brake fluid is not the problem whether it is DOT 3 Or DOT 5 silicone. The problem is air and water. The issue is how air/water issues are controlled. The ability of DOT 3 to absorb moisture is not a flaw..it is a government MANDATE. You can not sell orange juice and call it brake fluid. Brake fluid must pass a host of test relating to lubricity..boiling point..freezing point..viscocity..just to name a few. Hydraulic systems need some type of atmospheric compensation so they work at all elevations. Older systems are port vented. Newer systems have a compensation bladder. Moisture will enter an "open" system whether it has DOT or DOT 5 fluid. Permit my take on the problems of using silicone fluid.

Of the two issues around brake fluid..air and water..air can be the most troublesome as the effects are immediate. The EIS engineer shook a vile of DOT 3 and a vile of DOT 5 fluid to the point of air bubble saturation. The DOT 3 vile reconstituted almost instantly. The DOT 5 vile NEVER reconstituted. When you get air in DOT 5 it is forever. The only way to bleed DOT 5 systems is to gravity bleed. Many old cars have the master cylinder frame mounted below wheel cylinder level and can not be gravity bled. EIS did a perfect DOT 5 conversion to a 4 wheel disc brake Corvette and then loosened the wheel bearings a half round. Within 20 miles the calipers self-aerated the fluid to the point ot total pedal failure.

Water is a problem as the vent allows water into the system. DOT 3 controls water for a few years before a contamination level is reached. DOT 5 does not control the water. Globs of water can float in the system causing cylinder seizure...turn to vapor and compress in hard braking..or freeze and burst lines.

DOT 5 is not compatible with rubber. Old stock brake items..especially hydraulic stoplight switches fail rapidly. Any brake soft item exposed to DOT 3 and then DOT 5 will fail as well. A friend converted a Dodge Dart with disc brakes to a DOT 5 system. Within months the system failed with the rear shoes going into the drums. He neglected to change the balance valve and the o-rings failed putting disc pressure to the drum system.

The basic problem is owners that will change engine oil every 3000 miles will drive a car with 200000 mile brake fluid. The secret to hydraulic system life is an annual fluid purge. DOT 3 is not the problem...contaminated DOT 3 is the problem. Keep clean DOT 3 fluid in the system and it will last the life of the car without the danger presented by DOT 5.

Aris,

I find it's easier to answer with a lot of details the first time, it saves us trading messages back and forth.

Copper does not work in a hydraulic system due to the material properties of copper. The copper eventually fails. They do have a copper steel mixture that is used in some applications for brake lines. I don't know enough about this material to comment on it.

I used stainless steel brake lines on my Cord when I restored it about 15 years ago. Over here you can buy precut stainless steel brake lines in almost any local auto parts store. They are cut to standard lengths and already have the ends double flaired (and properly heat treated). All you have to do is determine the length you need and bend it to the right form. It saves a lot of work.

Jim

Thanks Jim, you sure covered every single aspect of it in every detail, so I guess if I go for a change to Dot 5, I will only do it whenever I overhaul the system along with new rubber parts as well. By then, there might be something newer and better around.
However, I took note of your remark on the copper brake lines. Mine are copper allright, but I I intalled them new, when I restored the car some 10 years ago. Do copper lines have a life time limit?
Aris

Hi Aris,

I've used the silicone brake fluid in my Cord for over 15 years with no side effects, but there are several things you need to watch out for.

First is the silicone (DOT 5) doesn't mix with the DOT 3. If you are going to switch fluids you need to flush out all the old fluid with alcohol and then put the DOT 5 fluid in.

Second watchout is the rubber in your system. The silicone brake fluid will cause the old rubber parts of the brake system to swell and your system usually locks up. If you've rebuilt you brakes system with modern rubber (hoses and pistons) in the last 10 to 15 years you should be OK. If not or you're not sure your best bet would be to completely rebuild the system.

The last item regards changing the fluid every couple of years. We need to go back to a basic difference between the two fluids and the differences between our old cars and the modern ones. The DOT 3 fluids are hydroscopic (I don't know if I spelled that right but it basicly means they absorb water out of the air). This was a safety issue in our old cars. The master cylinder in our brake system has a resevoir to hold some extra fluid. As we use the brakes the system pulls in some fluid and returns it to the resevoir (a very small amount). Since the resevoir is vented some air comes into the resevoir and moisture comes in with the air. The DOT 3 fluid will absorb the moisture (up to a point) to prevent water from getting into the system. Once the DOT 3 fluid is saturated we start getting water in the brake system and rusting. This is why we change the fluid every couple of years.

In modern cars the top of the resevoir has a rubber diaphram to prevent the moisture from getting to the brake fluid.

The DOT 5 brake fluid is not hydroscopic so any water that gets into the system will stay in the system in the form of water. For this reason it's a good idea to flush the system every few years.

The spongy feel comes from the DOT 5 fluid liking to entrain air and the air winding up in the brake lines. If you are going to use the silicone fluid you need to be carefull how you work with it. Let it sit for several days prior to filling your system (to get the air bubble out). Then be very carefull how it is added to the brake system to minimize any air bubbles. When I did my brakes I rigged up a system with a piece of tygon tubing to let me siphon the fluid from the jug into the master cylinder and I kept both ends under the fluid level to avoid any air bubbles.

One last tip - if you've never replaced the original copper brake lines on your Cord... DO IT NOW!!!

Have fun and keep driving!!!

Jim

Hi all! Some classic car owners around here are hot about Silicone-type brake fluids, that some call Dot 5. They claim it never needs changing and that there's no chance of it absorbing water with all the bad consequences that brings. I love the idea of not needing to change the fluid every two years and no rusted cylinders! I knew of racing silicone fluid with a higher boiling point, but back then you still had to change it every 2 years or so. The other question is, does it mix with Dot 3 and 4, or if one goes for the switch it is necessary to do a complete overhaul with new rubber parts? Has anyone tried it? Some say it has a ?spongy? pedal feeling and other side-effects.