The Stovebolt Site Forums The Shop Area Driveline Glycol vs Silicon Brake Fluids

I myself slant towards DOT 5 Silicon for my very nicely painted restorations, but its just an opinion. So many rumors out there concerning what and what not to use. Once you get to this site, check out the article in the first paragraph. I like math. I use it to formulate my opinions on politics, finances, chemistry, engineering, everything. Interesting stuff if you are trying to formulate what you think is best.

http://forums.mtbr.com/brake-time/silicone-based-dot5-busting-myth-832808.html

Bring it on!

If you do choose to run with Silicone fluid, you have to make 100% sure that all of the rubber components are rated for use with it. Most rubber parts made for passenger car and light truck use is designed to be used only with glycol based fluids, silicone fluids can damage them. Also, silicone fluids should never be used in any vehicle that has ABS, as it will cavitate in the ABS module (that isn't a problem with the trucks we deal with, though). It should also be noted that silicone fluids are compressible, which can give a slightly spongy brake feel, especially when the brakes are hot. While it does not absorb moisture (the common reason it's used in vintage vehicles), it also does not dissipate it like glycol does. That allows for any moisture that gets in the system to condense into water droplets at the bottom of the master cylinder and wheel cylinders, causing corrosion.
From a personal experience standpoint, I would not use silicone fluid in anything that did not have it as a factory fill. In a Harley, sure. In my Chevrolet trucks or any of my customers vehicles, no. There's simply no benefit to using it, and several reasons not to.

Betting your life on non-standard anything concerning brakes makes almost as much sense as drawing to an inside straight. Can we play some high-stakes poker, please?
Jerry

I must be lucky. I've had Dot 5 silicon brake fluid in my 39 for 15+ years. Never any problems. Brakes work as they should. When I do the general maintenance in the spring, I adjust the brake shoes, top off the MC if needed, and adjust the emergency brake cables. Sounds as if I may need that E-brake at some point.

I have used silicon brake fluid twice: In a 1973 BMW 3.0CS that I restored and my boat trailer. Neither have showed any adverse effects. I kept the 3.0CS for 10+ years after restoration and never changed the fluid. The brakes worked great (no spongy pedal) until the day I sold the car. I placed a big "STOP: use only silicon brake fluid" label on the brake booster next to the fluid reservoir.

The boat trailer brakes are still working fine as well.

I am debating internally on whether to fill my new (power front disk) brake system with silicon or conventional.

They use to have big write-ups back in the 80's and early 90's about using silicon brake fluid in collector cars. They said at the time government vehicles and the postal service used silicon brake fluid. Claim was no water absorption, rubber cups in the master and wheel cylinders lasted almost indefinitely, no pitting of master or wheel cylinders ect....
I have heard ABS systems are a no-no. And it seems closed brake systems are harder to get all the air bled out of the system with silicon. Almost need a pressure bleeder. Now in the old open single cylinder systems seems to work fine.
I have it in 2 "cars" now and so far no problems.

John

If you read that thread on the guys site I posted really well, I am having a hard time understanding why not use it. Its DOT (as in Dept of Transporation) approved and according to the article is safe on all internal brake components (rubber, neoprene, etc).

My big thing is the paint spoilage. I have spent almost a year perfecting the frame paint using 4 different coatings and several different coats. This is the second time I have done a frame up resto on this truck. The first time was brake fluid damage due to leaky, aftermarket brand new wheel cylinders.

It sounds like you neded to make that one a trailer queen, leave the brake system empty, and load/offload it for shows with a winch. Problem solved!
Jerry

Silicon does have that going for it, doesn't remove the paint. I did find I had a harder time getting the lines to seal at the fittings with. Whether it was because it was silicon or just me.
I'll probably continue to use it......

John

I used it in my Morgan for a season which included a few vintage races. Never had a problem with it. I did start with new everything so no issue with mixing with glycol. I got spooked by different things I read indicating it was not a wise thing for racing. Maybe I just didn't run hard enough to cook the brakes to that point. But anyway I switched back to glycol. If you were going to haul a trailer or otherwise work it hard, then it might not be a good choice. Otherwise, I doubt you will see a problem.

Dennis

Jerry, for you to be so adamant on not using it, you would rather not put anything in your truck and have NO brakes, there must be something the rest of us don't know.

My trucks are drivers. The military likes DOT5 because its easier to mothball a vehicle using it. They use the crap out of their vehicles with it. Other government agencies use the MIL-spec relating to DOT5. The flash point is higher, so making the brakes hotter should direct you to DOT5. That link I mentioned in the first post really makes if viable.

I always like to check with you guys because I have never been lead wrong by your advice. Especially if there is something you know that I don't.

I understand your concern about paint damage, but unless every piece of the brake system can be converted to modern-design rubber parts that are compatible with the silicone-base fluid, I'm concerned that you might be building in the possibility of a sudden, deadly failure. How about a failure of a flex line in traffic or something similar involving the failure of a wheel cylinder cup or a master cylinder piston seal? I doubt if it would be possible to observe the operation of an older style seal under load without some pretty extensive testing facilities. Simply soaking parts in fluid and looking for gross deterioration isn't sufficient where a safety-of-operation part is concerned.

I'd suggest using conventional DOT 3 fluid, and fabricating some sort of clear plastic shield to protect areas likely to be exposed to possible fluid contamination. That kind of concession to non-standard stuff on a restored vehicle isn't any more off the wall than doing a multi-layer frame painting procedure. I'm pretty sure your truck didn't roll off the assembly line that way, did it?
Jerry

Stoptech technical paper on brake fluid types. More brake fluid information.
As mentioned, my personal experiences with it have not been favorable. I originally put silicone fluid in mine, going along with the "benefits" that it was supposed to provide. I never had the spongy pedal, but after a year of having it in the system, I noticed a puddle under the truck. It turned out that the silicone fluid was leaking past the seals, as it had started to eat them. It also damaged the cups in the wheel cylinders as well. All of the parts were new, and had only been run with the silicone fluid. The wheel cylinders were ok after a teardown, thorough flushing, and new cups. The master cylinder however, required a complete overhaul, including honing out some rather nasty pitting from the moisture that had settled in the bottom. A call to the manufacturer revealed that they do not make parts that are designed to be used with silicone fluid. I went back to DOT3 glycol, and have not had a problem since.

I am not the least bit offended by these really spirited discussions on what is the best thing to use in any application. It gives us all more information to make a more informative choice. I like to be proven wrong because then I have SEEN what can happen and know not to make that choice in the future.

The paper on DOT 5 I posted in the first place says it works with all known rubber parts, has a higher flash point, and is used by the government a great deal. (That can be a good thing or a bad thing). The down side is bleeding can be harder because a normal bleed can keep air in the system. Everything else is anecdotal, but I will be VERY aware of any anomalies I find in the future. That's what I love about this forum.. we can disagree in a gentleman's way unless we are talking about dual MC's. LOL! Bill, I did read your link, thanks! In a year from now or a little more, I may be agreeing with you. Give me the opportunity to catch up!

Thanks for taking my admittedly biased opinion in the spirit that it's offered. I spent 30-something years trying to keep a bunch of high school auto mechanics "students" from killing themselves, me, or their fellow motorists with some of the ideas they got from the pages of Hot Rod Magazine, so I tend to be VERY conservative about using non-standard parts or procedures.

The one exception I make is for racing, where everybody out there on the track understands and accepts the risks involved. The soccer mom with a van full of kids didn't sign on to be the target of a 3-rail bank shot off a couple of other cars and a guard rail when somebody's suspension lowering job goes south, or a poorly-engineered air bag job puts a lowrider out of control. Ditto for the jacked-up rock crawler with 4-foot-tall lug tires somebody insists on driving on the freeway.

Your mileage may vary!
Jerry

One of my biggest heros in life.. either that or my biggest nemesis.. was my high school auto mechanics teacher. I learned so much from him. I went back years later to make sure he knew it. Trouble is, HE COSTS ME MONEY EVERYDAY!!! LOL!

My Suburban has had DOT 5 in it since 2003. No leaks, and no problems.

Before using the DOT 5, I replaced every part in the brake system with new parts (except for brass junctions/banjos). Before buying any part that had any rubber in/on it, I called the manufacturer to confirm that the rubber parts were DOT 5 compatible.

My only fear about the DOT 5, it that spillage/leakage would silicone-contaminate my garage, causing problems when painting this or other vehicles.

Most likely, I will use DOT 3 on the pickup I am restoring. It will have stainless steel lines, and it not be heavily driven, and it will be no problem bleeding the vehicle every year.

For those who are changing to DOT 5 and using old brake system parts, rubber parts that have been used with non DOT 5 might not respond nicely to DOT 5 (I think this fact has been posted above).

Amen to that silicon contamination fear. I paint in my garage and I am very careful when using any silicon product and I never use an aerosol silicon product. But, the silicon based dielectric grease that I put on critical electrical connections (i.e. grounds to bare metal) worries me and I am very careful and throw away the rag to wipe my hands immediately in the trash and then wash my hands. So far, no fish eyes in any of my paint jobs. I use silicon/grease remover religiously and even wipe down the air hose with it before painting.

Back to the subject at hand. I simply cannot make up my mind on what fluids to use in this old truck. Consequently, I have not filled anything other than the steering box with fluids. Just waiting it out...no diff, engine, brake, coolant, transmission, or any other fluid. I need a guidance counselor.

Yeah DOT 5 silicon is not compatible with regular brake fluid. Even the flex lines should be changed to new ones if they have had regular brake fluid in them.
The only thing I ever read that was a problem is the inline brake pressure switches used for activating the brake lights, for some reason the silicon would work on them. Not sure why. With these truck using a mechanical switch it isn't a problem anyway.
I must be totally wrong on all this if I'm agreeing with Deve...... LOL

John

Yeah, that's the general concensus. I put the DOT 5 in today. LOTS of leaks. ALL fixed pretty quickly and the system is really going to be clean. The only problem I ran into was one of the banjo bolts (front) didn't seat and stripped under my delicate supervision, so I had to order another bolt. Once its here, I can complete the bleeding process and GTG!

Had I used DOT 3 I would be crying right now since there were many leaks and the paint is ruined on contact. Its a no brainer when you are putting months and months into a paint job. Thankfully, I knew this and acted accordingly.

Another DOT 5 advocate here… But, ONLY when ALL parts are new; incl. rubber
lines. make sure you have the correct copper washers in those to prevent leaks.

I've got it in my panel (3 years), my 49 Willys (14 years), and my 58 Buick (forgot how many years), 35 Ford Street rod (24 years)….. no issues except for
the ones that have pressure type brake light switches… Silicone will compromise
them internally in less time than DOT 3. Usually they last for 2 or three years.
I keep a few on hand…. and they have loads of them at NAPA

my 2 cents