What's the negative of silicone/DOT 5 brake fluid?

What, if any adverse things should i know about? I'm using this soon in my coupe so the inevitable drips down the firewall don't lift the paint

 

I had it in a 67 Nova SS drum brake car. It was a new system except for the steel lines. I put silicone grease on the wheel cylinder pistons. It worked fine. The peddle felt soft but, the car stopped great.
I'm goin' to put it in the coupe when I get that far.
I heard that some of the in-line pressure switches don't last when usin' silicone fluid. I don't know that for sure it's just what I've heard.
I would not use it in a race car. It contains air and with alot of heat the air expands.
This will be an interesting thread. Smokey

 

I believe that it's still used OEM in Vipers, if that'll make you feel any better.

My dad has had it in his car for 25 years, no problems. Some people say that silicone fluid gives you a softer pedal. I'm not convinced.

Other than it doesn't play well with DOT3, I can't think of any downsides.

 

I've used DOT5 in all my cars since the 80's. If the changeover is done correctly, I know of no down side. I LOVE the stuff.

 

Strengths:
1) It has a high boiling point since it does not absorb water. Therefore, there's no so-called wet boiling point.

2) Doesn't absorb moisture.

3) Doesn't remove paint.

4) The viscosity is more stable over the extremes of temperature.

5) With the exception of some formulations used in external boots, silicone brake fluid is compatible with all standard brake components.

Drawbacks: 1) It's hard to pour without entraining air bubbles--hence an application will generally have a softer, spongier pedal feel.

2) It doesn't absorb water, so any water already in the system accu-mulates in the lowest point of the system and stays there, causing rust.

3) Glycol fluids begin to compress near their boiling points, whereas silicone fluids begin to compress at around 300-350 degrees Fahrenheit.

4) Additives in the fluid can vaporize at comparatively moderate temperature, increasing the spongy feel.

5) Silicone fluids expand significantly when hot.

6) Silicone fluid is functionally incompatible with systems that have held glycol-based fluids for any length of time, requiring flushing and seal replacement (there are counter opinions on this, which state that the modern silicone formulations are in fact compatible with only a flushing, rather than a complete reseal). The actual DOT specification requires chemical compatibility, so as far as that goes, the two fluids won't cause reactions if used in the same system, but they certainly won't mix, either.

7) It's pretty much incompatible with anti-lock brakes because the silicone fluids tend to be more viscous, which can cause problems with the timing of the pulses that are intended to work with the thinner glycol-base fluid. This sometimes leads to damage of the ABS valving. The rapid pulsing necessary to anti-lock functions tend to cavitate the fluid, as the tiny bubbles collapse and coalesce into larger ones, and then collapse and reform into smaller ones. This tends to counteract the ABS effect and can diminish the actual effective braking. This condition also heats the fluid and can lead to even more sponginess and possible damage to the ABS controller. Thirdly, silicone brake fluid tends to foam when expressed from a small orifice under pressure, reducing its hydraulic effectiveness greatly. <!--end article--><!--END CONTENT-->

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I had it as Factory install on a Harley FLHS. Rode out to Colorado and into the mountains (like you do). Lost the rear brake completely, and the front was so spongy that the lever came up agin the bar and the bike stopped terribly. Nothing to do but ride back down, and the brakes came back acceptably. Bled the snot outta the system, loads of air, then rode back up the next day.

Same shit. Exactly the same.

Bled the brakes again, and gave up.

Silicone holds air, hell it is known to suck air in past the seals in the average caliper just with the little movement that rotor runout makes. And you need runout for proper pad kickback.
And air expands at higher altitude, which is why I lost the brakes every time I went up.

Note that every one who uses silicone and is happy has either drum brakes or lives in the flatlands. There is a reason for this.

Note, too, that silicone is specifically advised against in most ABS sytems.

I wouldn't use it. I don't use it.

Cosmo

P.S. The last time I tried using DOT 4 for paint removal (emergency), it didn't work. Think about that, too.

 

I will support what cosmo wrote. I had it in a car and didn't see the warning label on the jar about air entrained in the fluid. The advice was to heat the fluid to boil all the air out. Anyway, I drove over the Sierras and sure enough lost the pedal. As I came down into Reno the pedal came back until it was firm again after a few days of driving. I will state that the pedal didn't go away as much on the return trip but at Laguna Seca the pedal went away again due to all the heat. The main reason I see to use it would be it's paint friendliness. Otherwise, stick with DOT 4.

Joe

 

Only problem I ever had, was brake light pressure switches will go bad usually with in a year. Install a lever switch on brake pedal and your good to go,

 

if silicone fluid leaks onto a primered body you will not get paint to stick to it.....a friend learned this the hard way

 

I used it and had a very very hard time getting it to bleed. never did get the brakes right before i sold the car.

 

i've used it in everything for the last 20+ years...i've never had a problem

 

I've used it for the last 5 years in my car...love it. Make sure you flush your system and replace all rubber components - although it's supposed to be compatible it can cause older rubber to swell.

I've never noticed a spongy feeling - and have never had to bleed my brakes other than the initial filling of the system.

 

Could the air be boiled out if a container of fluid was put into a vacuum chamber? Anyone tried this?

 

I've used it for over 15 years on 3 different cars, drum and disc brake system. Each time I replaced all metal and rubber lines, replaced wheel cylinders and the master, never had another issue with brakes again.

Works for me.
Dennis

 

I've been a mechanic for the U.S.P.S. since '83.
The Post Office has used DOT 5 ever since I can remember.
To be honest in the three Post Office garages I've worked at during this time we had few if any problems using DOT 5.

 

If silicones good for tits its good with me.

I like tits fake or not

 

I work for GE making pressure sensors. We use silicone fluid as a means to transfer pressure in an enclosed system. We pull a vacuum on it for 4 hours before use.
Even at base pressure(2x10-2 torr if you are familiar with high vacuum) it continues to outgass for several hours under heat and stir conditions. I assume doing this before putting into your system would eliminate 95% of the air.

Craig

 

Had it in my first roadster. Worked great around town and where I live. Took off on a cross country trip and lost my brakes every time I was over 5000 feet. Change it ASAP.
Cleaned out the lines with alcohol and put in Dot 3. Never had any problems after that.
So if your a flat lander, it will work great till you head for the hills. Its scary when you hit the peddle and nothing happens..............

 

I used silicone fluid in my 37 coupe when I built it.I had a somewhat soft pedal,but thought it was just the nature of the beast.Was in Bakersfield one summer--about 110 degrees--and the brakes would lock up in traffic.I cracked the bleeders on all 4 wheels,and it spit pressure out.I did this 5 or 6 more times on a 2 hour trip home.After that,I flushed it out and put in Dot 3--never had another problem.
A friend tried it in his car--worked ok for about a year--then the same thing happened.
Just my $.02

 

I love it and use it for everything I have, it just cost more !

 

I used it for several years in my roadster when it was new and had most of the same problems mentioned above. I switched and have used DOT 4 ever since with no prblems.

 

I put it a car over 30 years ago and it still works fine. Don't know about altitude problems. You do have to carry an extra brake light sensing/sending switch to change about once a year tho. Did you know that one drop of silicone at the base of a house door jam can be detected at the top of that jam a year later! So if spilled before painting a car will require a lot of prep to remove. TomK

 

I've run silicon fluid in my 32 since 93 when it first went on the road.
It was the initial install.

Never had a problem at altitudes up to 6000' or so.

Heck the FAA allows it in light aircraft.

No probs driving the mountains either.
2400# car, 11" Mustang discs up front and 11" x 2 1/4" Merc wagon drums out back.

I wonder if some of the lost the brakes in the mountains comments could be due to driving technique . . . or simply driving fast.

I like to gear down in the mountains and let the engine hold it back.
Some of my pals don't.
One even leaves his 3/4 ton pickup in OD and uses brakes only.
Sometimes I think he ain't real smart and other times I'm sure about it.

That said, I'm planning on using Dot 4 in my 31 roadster and found the "no paint damage" comments interesting.

The reason hydraulic stoplight switches fail is the silicon fluid emigrates into the sealed switch area and insulates the contacts one from the other.
It only takes a couple of weeks until the stoplights don't work unless you have the brakes at full lockup.

Mechanical switches are the way to go here.

Sealing at tubing fittings can be difficult at times.
Whether factory done by Burndy or a good double flare tool by a fairly experienced operator.
If you join lines use steel fittings and not brass.

Note that factory cars use steel and it's not just because steel is cheaper....

 

I put in in my roadster 2 years ago from day one with everything new. I had a spell of the pressure type stop light switch sticking but thought it was too sensitive and changed it. no other problems with my drum brake system.

 

Stu D Baker
Seems to have the best tech on the usage. My experience with silicone fluid has been a good one with my street cars as well as one of my nostalgia race cars. Since I have old cars and nothing with ABS I cant make comments as to new car applications. Over 25 years with the silicone with zero failures which has included stops on the track at 190+. When I went to silicone it was with reason to stop the severe rusting of the brake system from sitting to long without use. I did the usual total flushing of the system and replace every rubber part and a good final flushing and to date never a single hard peddle or cup or MC leakage. One response referred to high altitude brake loss with silicone and I only had one of my cars in mountain country (Colorado) and went all over and again I saw no problem. I will stick to it until I experience problems.

 

Been using it on my bikes for years with no issues. Installed a new brake system on my hot rod build and couldn't be happier with it. Good braking and easy on the painted surfaces.

 

The Negative of conveting to Silicone, would be I'd have to drain out the old, throw away some good stuff, and to what end? To pay more?, with no apparent advantage.

In any car I have ever owned. No brake malfunction that I have ever had was caused by the composition of the fluid, except one time somebody inadvertently put motor oil in there.

I don't LOVE dot3, but it works great, has never failed me so I have no need to switch.

Don't use brake fluid in Nash HotRod.

 

There is a good reason the major manufacturers do not use it. Silicone brake fluid needs to have neoprene or synthetic seals. Read the warnings on the can. It slowly creeps past rubber and hey presto - no brakes. Happened to me when I lost all my brakes and nearly took out the NSRA Safety Tent at 5 mph - on NSRA Appreciation Day!

All this talk of 'been using it for years and never had a problem...' well on Dec 25th 2004 people had been living in S.E. Asia for thousands of years and never had a Tsunami that killled 300,000 people either, and in 1986 they had never had a nuclear accident in Chernobyl either. Just because it hasn't happened, doesn't mean to say it won't.

I would not use that shit ever - it has no noticeable advantages for street use and you cannot top it up with regular brake fluid. Talk to a brake manufacturer such as Baer, Brembo or Wilwood, before you think about using it.

How much do you value your car and your life?

 

First car I used it in was a '59 Metropolitan that I had done a complete brake overhaul on. The car had sat for 19 years, and I replaced everything and used the DOT5 silicone fluid. I also used it in the hydraulic clutch unit, since I had replaced both the master and slave cylinders there. Worked like a champ!

BTW, with ANYTHING, there are going to be people that have had absolutely no problems with it, and others that compare it to the Apocalypse, so weigh each, and go with what you are comfortable with.