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SILICONE BRAKE FLUID -GOOD OR BAD ?
Posted by: Melb-Mike ()
Date: May 14, 2017 06:45PM

On an other forum, I got into a discussion on the merits of various brake fluids. It all boils down(no pun intended) on Glycol based vs Silicone.

Some have said since silicone won't absorb water, it is actually worse than glycol based (DOT 3, 4, 5.1) fluids. The claim is based on the fact that water is heavier than silicone fluid so it will go to the bottom f the master cylinder and end up as water pockets in your wheel cylinder or caliper, thus causing even more rust. Also, it is claimed silicone fluid holds air bubbles more than glycol based fluids so you will have a soft mushy pedal.

On the side of silicone fluids, the argument for its use are;
1) silicone fluid coats all netal surfaces and will prevent rust
2) silicone is stable for decades, doesn't destabilize
3) silicone is now used on military vehicles with improved maintenance performance
4) once silicone is properly bled of air, pedal feel is as hard as glycol based fluids (requires the use of a power bleeder to get effective air bleeding)

My 69 Corvette had relatively new calipers fail with glycol. I switched to silicone and braking is excellent but it's too soon to report on long term use. I switched my 64 Greenbrier to silicone brake fluid and couldn't be happier. We even had a group of riders in the Helen Springfest rally event going up and down mountains without any brake issues. I just switch my Ford Cobra roadster to silicone and I'm thrilled with the braking performance and very firm pedal.

So, some of you guys know 100 times more than I ever will, what do you think ?

64 Greenbrier
64 Spyder (needs restoration)
65 Corsa 140, restored
66 Corsa turbo, restoring now
66 Corsa 140 "RR" code coupe fully restored
67 Pontiac GTO restored
69 Corvette 427 convertible restored
2004 Caterham R400 (Lotus super7)my race car
2004 Porsche 996TT convertible
2015 Corvette Z06
1965 AC Cobra (Factory Five)

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Re: SILICONE BRAKE FLUID -GOOD OR BAD ?
Posted by: mwr ()
Date: May 14, 2017 07:20PM

I think use the search function, I remember this discussion has popped up several times in the past.

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Re: SILICONE BRAKE FLUID -GOOD OR BAD ?
Posted by: Nickshu ()
Date: May 14, 2017 07:29PM

From what I have read and been told if you ever drive at altitude it's unsafe to run silicone brake fluid.

Nick
_______________________________________________________________________
1964 Monza Spyder Convertible #435 - Rotisserie restored - Check out my restoration thread here: [corvaircenter.com]
Recreational Mechanic/CORSA Member/US Navy Veteran
Other cars: 2003 Porsche 996.2 Carrera; Boring daily drivers; Serpent Express 18' trailer; 2005 Lotus Elise supercharged (SOLD); 1982 Porsche 911SC (SOLD)
Northern Colorado, USA

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Re: SILICONE BRAKE FLUID -GOOD OR BAD ?
Posted by: Brizo ()
Date: May 14, 2017 08:07PM

I think silicone fluid was developed for use under severe conditions like racing. I don't think the use of either fluid on the street is either good or bad. But its interesting that even the latest Corvettes, with optional six piston calipers and carbon rotors come with DOT-3 fluid.

Dan Brizendine,
'64 8door Greenbrier 140 PG. "In beautiful Wanamaker Indiana...with one stop light and 5 pizza shops"

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Re: SILICONE BRAKE FLUID -GOOD OR BAD ?
Posted by: CoCoCo ()
Date: May 14, 2017 08:45PM

Never had any of the issues stated with silicone in any of my trucks or Corvairs.
Granted, I live in a relatively dry climate, so general moisture issues are not as prevalent as they can be elsewhere. And we (dad and I) always tended to bleed a brake for one reason or another, so the water buildup settling down at the brake ends would not have occurred either, unless it's supposed to happen quickly?
If it's a long-term issue only, then our constant fiddling with things is probably what saved us from any long-term buildup.

One bad thing that I see though, is if you're not into totally flushing the fluid ever few years like most of us should do (or simply replacing it, not necessarily "flushing" the system) then the fluid itself does not give you any indication.
I was one of those that would replace fluid if it ever became really ugly and opaque, but even then would tend to wait awhile. With the silicone fluid there was never any discoloration or buildup of anything in the master cylinder that you could see. So clear fluid, no need to change...
But even with silicone I'm sure you would see the benefit of the cheap insurance that is changing the brake fluid every few years or so.
Even in a wetter environment that maintenance might do away with the bad point about the buildup down at the wheels.

But no matter what, my personal experience has been stellar. Super firm pedals in every vehicle, with no known deterioration of seals or rubber lines that I've been able to tell.
Vehicles so far were a Ford Bronco, a Ford F350 pickup, one early and one late Corvair. All with basically stock braking systems.

Can't say I'm recommending it to everyone, but in my case it has worked well.

Paul

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Re: SILICONE BRAKE FLUID -GOOD OR BAD ?
Posted by: Frank DuVal ()
Date: May 14, 2017 08:53PM

Late model stuff has that there ABS equipment that needs the lubricity of DOT 3. That's why the new Corvette still specifies it.

I will say again, I have been using DOT 5 Silicone fluid in every pre-ABS braking system I have rebuilt since Clark's started selling it in the late 70s or early 80s. Corvairs, Buicks, Chevrolets, Grahams, Studebakers, Packards, you name it.

I have NEVER had an issue with installing or using it. Never used a power bleeder.

Living on the east coast with humidity, never had a rust out problem with DOT 3 from the inside of the steel tubing. I do not understand the "holds water to cause rust idea". Makes NO sense. DOT 3 , 4, 5.1 are hygroscopic and absorb water right out of our air, causing rust and corrosion.

Use DOT 5 and you will never see that horrid white crap in wheel cylinders again!

Sure one should flush DOT 3, 4, 5.1 every 2-3 years, but who really does that?

20+ years later, my DOT 5 systems are working just fine.

Sure, racing and high altitude (Pike's Peak) drivers should know the issues with that. Regular drivers, not a problem. But I do not live in Colorado!

I suspect some issues with DOT 5 are installer error. Ever since I saw a Corvair owner help bleed a break system by "pumping" the brake pedal like a Gatling gun, I see where crap information comes from. That guy would have made DOT 5 look like a foamy mess. grinning smiley

Frank DuVal

Fredericksburg, VA

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Re: SILICONE BRAKE FLUID -GOOD OR BAD ?
Posted by: CoCoCo ()
Date: May 14, 2017 08:59PM

I wonder if some of the high-altitude issues were simply the pressure changing the characteristics of air (or even moisture) that was already in the fluid. As you said, installer error.
No idea, but I never had any altitude related issues either.

I've had my trucks up at 9000' and then some, with no noticeable ill-effects. Both Corvairs up to 7000' and having some fun on the mountain roads.
Not for any extended periods, but certainly under some "interesting" circumstances.

Paul

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Re: SILICONE BRAKE FLUID -GOOD OR BAD ?
Posted by: dolomitefan ()
Date: May 15, 2017 01:12AM

This debate often comes up over here in Europe and opinion is just as split. To many DOT 5 Silicone fluid is idea because it doesn't absorb water which reduces corrosion in the cylinders, pipes and calipers.

I sort of subscribe to this thought, however there are some huge disadvantages.

Firstly though it does not absorb water any moisture present in the system will find its way to cylinders and calipers, and will cause corrosion in those components. Your system should ideally be fully new, dry as a bone before adding the fluid.

Then there's pedal feel. It does not work as well as regular brake fluid and you'll find you often have a longer pedal travel with less feel. Fitting braided hoses will help to improve the feel but do expect the brakes to feel different those those using regular fluid.

My car has a fully renewed braking system but I'm yet to decide what type of fluid to use.

Incidentally you wouldn't want to use silicone in a race car, it was actually developed for aircraft to minimise corrosion and maintenance. In a race car you'd have zero confidence in your brakes.

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Re: SILICONE BRAKE FLUID -GOOD OR BAD ?
Posted by: JimBrandberg ()
Date: May 15, 2017 02:30AM

I use DOT 3.
Jim Brandberg
Isanti, MN
CorvairRepair.com

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Re: SILICONE BRAKE FLUID -GOOD OR BAD ?
Posted by: Spectre ()
Date: May 15, 2017 04:15AM

The '66 I used to own had silicone fluid. Performance was perfect and you'd never suspect anything was different. I owned that car from 1997-2012, and from '97-'05, it was a daily driver.

David Clamp


1965 Corsa convertible - 140 4spd/3.55/AM-FM

2013 Mustang GT convertible - 5.0, 6spd auto, Procharger i-1

2003 Miata SE - 6spd manual (wife's toy)

"Victory is mine!" - SG

Warner Robins, GA (15 miles south of Macon)

Click for Warner Robins, GeorgiaForecast


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Re: SILICONE BRAKE FLUID -GOOD OR BAD ?
Posted by: jjohnsonjo ()
Date: May 15, 2017 05:30AM

I've been running DOT 5 in my Vair since the late 90s. No issues, very hard peddle. I check it once a year, looks like new.

When I did it, everything was new. Also, you must pour slow and take your time bleeding to reduce the risk of air bubbles.

The reason some new cars including my motor home recommend DOT 3, is that even though DOT 4 starts with a higher wet boiling point it will absorbed water more quickly than DOT 3 and will soon be lower. Also, some DOT 4 is hard on Dot 3 seals.

J.O.

65 Corsa Turbo Vert
79 Honda XL 500S
69 Honda CL 160 D
2010 BMW F 650 GS
2003 Bounder 36D
2013 KIA Optima SX turbo-AKA ZIPPY (wife,s car)
69 Newport Holiday Sailboat
Baja 150 dune buggy cart
Coleman HS 500 UTV
2016 KIA Sorento SXL Turbo

Bethlehem,Pa

Image and video hosting by TinyPic

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Re: SILICONE BRAKE FLUID -GOOD OR BAD ?
Posted by: Melb-Mike ()
Date: May 15, 2017 05:31AM

I think the soft pedal claim is from air bubbles remains in the system with the silicone fluid. After I flushed everything out of the greenbrier I installed a new master cylinder and hoses to each wheel, then put silicone fluid in the system. I used the power bleeder and had a semi-soft pedal. I let it sit that night and the next morning bled the system again. To my surprise I got a good bit of air from the right rear wheel cylinder. I did all the wheels and only got a bubble here or there of air. I went and checked the brake pedal and now it was rock solid. Braking was excellent on the road.

I think the silicone will "hold" air bubbles longer than DOT 3 or 4 so it may require a period of time to sit and then rebelled.

Silicone is used in other applications to disperse or displace water. Dielectric grease is used on electrical connections to keep water from corroding the connection. Dielectric grease is silicone. O-rings used in swimming pool applications are lubed with silicone grease so obviously there isn't a deteriorating effect on buns-n rubber products.

With regards to Corvette's 6 piston calipers using DOT3, that is correct. However when I was racing my 2007 Z06, I had to change to high temp DOT 4 Motul RBF600 fluid to keep brakes working. Most Corvette owners never run on the track or even drive their cars hard. I was the exception.

64 Greenbrier
64 Spyder (needs restoration)
65 Corsa 140, restored
66 Corsa turbo, restoring now
66 Corsa 140 "RR" code coupe fully restored
67 Pontiac GTO restored
69 Corvette 427 convertible restored
2004 Caterham R400 (Lotus super7)my race car
2004 Porsche 996TT convertible
2015 Corvette Z06
1965 AC Cobra (Factory Five)

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Re: SILICONE BRAKE FLUID -GOOD OR BAD ?
Posted by: gnvair ()
Date: May 15, 2017 05:41AM

The 2 downsides to silicone vs conventional DOT3 or DOT4 is
if the wheel cylinders weep/seep/leak fluid on to the shoes you will have to throw them out as no amount of solvent will ever get it out of the linings.
Next is local availabilty. If you drive your car long distances and are in a situation where you might need to add fluid there is a good chance you won't be able to get the silicone fluid as easily as DOT3 or DOT4.
Other than that it is personal preference. My own cars all have stainless steel brake hard lines that will outlast myself and the cars.

Lee J
Southern New Jersey near Philly.
1966 Corsa 180/4 speed
1969 Monza convertible 140/4 speed

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Re: SILICONE BRAKE FLUID -GOOD OR BAD ?
Posted by: jjohnsonjo ()
Date: May 15, 2017 05:54AM

Most all FLAPS I have been in have DOT5, right next to the regular stuff, small cans only, but I have a spare.

J.O.

65 Corsa Turbo Vert
79 Honda XL 500S
69 Honda CL 160 D
2010 BMW F 650 GS
2003 Bounder 36D
2013 KIA Optima SX turbo-AKA ZIPPY (wife,s car)
69 Newport Holiday Sailboat
Baja 150 dune buggy cart
Coleman HS 500 UTV
2016 KIA Sorento SXL Turbo

Bethlehem,Pa

Image and video hosting by TinyPic

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Re: SILICONE BRAKE FLUID -GOOD OR BAD ?
Posted by: curt ()
Date: May 15, 2017 07:29AM

Opinions on both sides, I use the DOT 3 and bleed the brakes every few years.

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Re: SILICONE BRAKE FLUID -GOOD OR BAD ?
Posted by: Jim Stukenborg ()
Date: May 15, 2017 07:45AM

Delco Moraine, GM's brake division, was all set to release silicone brake fluid until they ran the Pikes Peak test. The tiny air bubbles that are present in the fluid expanded at the low pressure of high altitude and the brake pedal went to the floor. Since it wasn't possible to get rid of all these tiny bubbles and GM could not sell cars that one could not take to high altitudes, the use of silicone fluid died.

One big advantage of silicone fluid for GM was that if any leaks took place during transit it does not damage the paint of the vehicle that might be under the leaking vehicle.

My V-8 Corvair has used silicone fluid for 15-20 years before I bought it and I have had it for 16 years without any brake system problems.

Sort of reminds me of the Viton "O" ring situation. GM supposedly had knew that Viton worked well hot, but not so well at low temps. Since they were concerned with cars driven in real cold areas everyone got regular butyl rubber seals. We know what problem that caused. Jim

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Re: SILICONE BRAKE FLUID -GOOD OR BAD ?
Posted by: 66vairman ()
Date: May 15, 2017 09:21AM

Lots of opinions and anecdotal evidence.

The issue with the early silicone brake fluids was composition and no DOT oversight. I had good luck with some, but one brand literally turned the master cylinder and wheel cylinder seals to black MUSH!

After years of reading I discovered that ALL brake fluids need to be changed per the manufactures recommendation. On a hobby car that sits a lot the fluid should be changed every couple of years, including silicone fluids.

Yes regular brake fluid attracts water, but it actually ABSORBS moisture in a system and prevents corrosion UNTIL the fluid is saturated - that's why it has to be replaced. Any fluid leaking around seals will attract moisture and cause corrosion - it's bad seals, not a problem with the brake fluid. Any moisture that finds it's way into a silicone brake fluid system will condense and cause corrosion. This is especially a problem with old open systems from the 40's and 50's.

A lot of the aftermarket brake seals only tolerates DOT3. The newer DOT3 brake fluids have nearly the same boiling point as the DOT4. So no need to use DOT4 and it may not be compatible with brake items labeled DOT3 (most of the aftermarket parts for a Corvair).

The DOT requirments are only for performance and DO NOT CONTROL chemical composition of a fluid. Some DOT 4 fluids work in a DOT 3 system, some DO NOT. ALL DOT3 fluids work in a system rated DOT3.

Now I use DOT3 in my Corvairs and flush the brake system every couple of years and I have no problems.

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Re: SILICONE BRAKE FLUID -GOOD OR BAD ?
Posted by: Seth Emerson ()
Date: May 15, 2017 10:38AM

"What do you think?" is asking for anecdotal evidence, after all. No racecars run Silicone fluid, but we change the fluid often. Performance - especially at high temps is everything. For older "collector" cars, are you going to flush and replace the fluids every year? BE HONEST! - And how many are driving to Pikes Peak? If the system is flushed and clean, DOT 5 Silicone works fine in regular - or even irregular service. And you can keep a partial can with you for a trip - (Not for DOT 3, it self-contaminates with water, once the can is open.)

Seth Emerson

Check my new Performance Corvair Web site [www.perfvair.com]

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Re: SILICONE BRAKE FLUID -GOOD OR BAD ?
Posted by: Melb-Mike ()
Date: May 15, 2017 11:29AM

You're right Seth, I am asking for anecdotal evidence. All forums do. Few of us are scientists but we all have experience, good or bad, with these older cars. Again you're correct to point out that most of us have no intention of running Pike's Peak, most of us have never been there. I was trying to see if anyone ran into corrosion or rust issues that could back up the claim some have made about the fluid shoves water down and isolates it against metal. I had not seen or experienced that.

One very good point made was that if a wheel cylinder leaks onto the brake shoes or pads, you'll have to throw them away. By the same token, any metal coated with silicone initially seems to be protected from future rust, but this is just a guess on my part.

Also, I woukd hesitate using silicone fluid in a ABS equipped car, and it seems most newer cars are equipped with it.

With regards to silicone developing air bubbles at higher altitude or temps, I don't think it's correct. If it wasn't bled completely, there would still be air bubbles and yes, they would expand at higher altitude or temperature.

64 Greenbrier
64 Spyder (needs restoration)
65 Corsa 140, restored
66 Corsa turbo, restoring now
66 Corsa 140 "RR" code coupe fully restored
67 Pontiac GTO restored
69 Corvette 427 convertible restored
2004 Caterham R400 (Lotus super7)my race car
2004 Porsche 996TT convertible
2015 Corvette Z06
1965 AC Cobra (Factory Five)

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Re: SILICONE BRAKE FLUID -GOOD OR BAD ?
Posted by: corventure Dave ()
Date: May 15, 2017 12:23PM

I also have used DOT 5 in my Corvairs for 40+ years. I have never had any moisture or performance issues. The Corvair brake system is closed, unless the master cyl. cap seal is compromised. The fluid in my Corvair's stays clean and clear for many years, and brake performance is maintained. Rubber parts seem to be preserved and look near new, even after 20-30 and even 50,000+ miles of use. This is with most common vehicle usage.
I agree that if there is a wheel cyl. leak and the shoes get contaminated... they will have to be replaced. But I practice them even with standard DOT-3 or DOT-4 brake fluid contamination. Brake shoes are not that expensive.

My advice is to use your best judgment. For me and vintage drum brakes.....
#1 replace all components with new and I then use Dot-5 Silicone fluid.

Corventure Dave

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