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Silicone brake fluid revisited
Posted by: Jim Stukenborg ()
Date: December 15, 2017 01:34PM

During our last discussion on silicone DOT 5 vs regular DOT 3 brake fluid, I mentioned that silicone fluid has entrapped air from the manufacturing process and when GM was getting ready to release the silicone for production use years ago they ran a Pikes Peak test and experienced loss of pedal at the top of the mountain. This killed silicone fluid for production use. One of the responses to the post said that it was just a poor bleed job. So here is the visual proof that silicone contains air. This picture was taken in a clear vacuum chamber at partial vacuum since the air pressure at the top of PP is about 60% of sea level.I don't have a comparison pic from 40 years ago, but the picture shows bubbles from the entrapped air coming out of the purple silicone brake fluid on the right.There are no bubbles coming from the DOT 3 on the left. The silicone fluid was recently purchased.

The only way we will know if this amount of entrapped air in the current silicone will cause a loss of brake pedal is for someone in Colorado with silicone brake fluid to do a test run up Pikes Peak and report back. Maybe Steve Goodman in the Denver area will do the test. A Corvair is a good test vehicle. Light weight, good parking brake, and a big rear brake for the vehicle. If you lose the pedal you will have to use the hand brake to get back down the mountain, or maybe one could trailer the car up to the top and do a pedal check. Now if you do not plan to drive up Pikes Peak this is all a moot point. Silicone works fine at lower altitudes. What do you say Steve? Jim

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Re: Silicone brake fluid revisited
Posted by: Pedigo ()
Date: December 15, 2017 01:43PM

How many different jets does it take to get to the top of Pike's Peak?
(That's a real question)

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Re: Silicone brake fluid revisited
Posted by: Jim Stukenborg ()
Date: December 15, 2017 02:08PM

Pedigo, when we ran brake tests on PP we did it at gross vehicle weight. At altitude the small cars really struggle loaded. You have to slow up to make a turn and the engine sits there against the stall speed of the auto transmission an doesn't pick up speed until you get a little change in slope of the road. One story I heard was that the driver and observer jumped out of the car doing several mph to lighten the load until it started to pick up speed. Don't know it was true, but I did feel like doing that on our run up the hill. Jim

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Re: Silicone brake fluid revisited
Posted by: red monza ()
Date: December 15, 2017 02:10PM

My new 64 conv has had a complete change from Dot 5 back to Dot 3....much much better stopping now.

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Re: Silicone brake fluid revisited
Posted by: jastranc ()
Date: December 15, 2017 03:00PM

I have run DOT 5 for 16 years in my 69 with no bad results and my 64 and 66 both ran it for years.In 2011 while attending the convention we took the 69 up Pikes Peak with no issues.I might add my 69 had new brake system in when installed.That means new MC,all lines,wheel cylinders,hoses and shoes.Other Corvairs I just flushed the system.
If you use DOT 3 they say you flush the system every 2 to 3 how many people do that?
Do what you want but for me it is all I use in my classic cars.I might add I use a Military Grade of Silicone fluid that was made by Dow Chemical.

Jim Stranc

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Re: Silicone brake fluid revisited
Posted by: Richard ()
Date: December 15, 2017 03:52PM

It isn't that DOT 5 contains Air, The problem is that it is easily aerated. It can be aerated when shaken, driving home from the store or even when poured. That is why some have a soft pedal after bleeding.
That is why most DOT 5 products say not to be used with ABS. The ABS pump churns it up.

Unverified, but I read that the Military is going to stop using it.

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Re: Silicone brake fluid revisited
Posted by: corventure Dave ()
Date: December 15, 2017 04:32PM

Having trouble imagining how in a closed brake system air can get agitated into the brake fluid. The master Cyl would have to be mounted in some kind of off road vehicle. And then, how would the air gravitate "down" to the wheel brake cyl's?

Interesting information however!

Corventure Dave

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Re: Silicone brake fluid revisited
Date: December 15, 2017 05:16PM

Looks like a good test, but I do have a couple of questions. What is the vapor pressure of silicone fluid? If you did the same thing with gasoline, wouldn't you get bubbles even though there was no air trapped in the gasoline? Could the bubbles be vaporized silicone, rather than entrapped air?

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Re: Silicone brake fluid revisited
Posted by: joelsplace ()
Date: December 16, 2017 08:55AM

If it was it would cause the same problem wouldn't it? Interesting question anyway.

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Re: Silicone brake fluid revisited
Posted by: Jim Stukenborg ()
Date: December 16, 2017 03:59PM

It looks like Steve Goodman is off the hook on the Pikes Peak test since Jim Stranc has already run the vehicle test. Jim, to answer Pedigo's question how did the Corvair run near the top of Pikes Peak? Jim

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Re: Silicone brake fluid revisited
Posted by: vairmech ()
Date: December 17, 2017 04:41AM

BorondaFarmRacing Wrote:
-------------------------------------------------------
> Looks like a good test, but I do have a couple of
> questions. What is the vapor pressure of silicone
> fluid? If you did the same thing with gasoline,
> wouldn't you get bubbles even though there was no
> air trapped in the gasoline? Could the bubbles be
> vaporized silicone, rather than entrapped air?
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Without looking it up I can tell you that the vapor pressure of DOT 5 brake fluid is WAY higher than any gasoline, other than aviation fuel maybe.

For those of you out there that swear the DOT 5 is what you use, good for you. Personally I don't like the feel of the pedal after installing it. Yes there is a difference in pedal feel. With the DOT 5 fluid I cannot control the amount of braking modulation in the race car.

Now the question, does moisture get into the brake system when using DOT 5 fluid? The answer is STILL yes. It just doesn't mix with the fluid.

Ken Hand
Handy Car Care
248 613 8586

Vairmech@aol.com

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Re: Silicone brake fluid revisited
Posted by: Pedigo ()
Date: December 17, 2017 07:00AM

vairmech Wrote:
-------------------------------------------------------

> Now the question, does moisture get into the brake
> system when using DOT 5 fluid? The answer is STILL
> yes. It just doesn't mix with the fluid.


Is the MC the cuprit here? For both moisture and airation?

Moisture=condensation building up on the inside of the MC above the fluid level due to thermal cycles.
Airation=vibration of the MC on rough roads,therby mixing the fluid and the trapped air above the fluid,(creating micro bubbles)and getting introduced into the lines when applying brake.



Edited 1 time(s). Last edit at 12/17/2017 07:02AM by Pedigo.

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Re: Silicone brake fluid revisited
Posted by: joelsplace ()
Date: December 17, 2017 07:46AM

I wondered about the moisture. With DOT5 doesn't it just sink to the bottom and cause problems faster than regular fluid?

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Re: Silicone brake fluid revisited
Posted by: Pedigo ()
Date: December 17, 2017 08:08AM

I intentionally used DOT5 on my brand new brake system to "avoid" the potential of moisture contamination. The bleeding process was lengthy to rid all micro bubbles from the system,but well worth the effort. Always had a strong pedal feel since,and I feel confident braking in any condition,no matter the situation.
(When your knees are the crumple zone,you REALLY think about confidence)



Edited 1 time(s). Last edit at 12/17/2017 08:09AM by Pedigo.

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Re: Silicone brake fluid revisited
Posted by: Frank DuVal ()
Date: December 17, 2017 10:55AM

OK, vapor pressure of DOT 5 is .07 mmHg @ 68°F.

Vapor pressure of gasoline is 275-475 mmHg @ 68°F

[championbrands.com]

[www.co.vermilion.il.us]

Last time I checked my math books, .07 is waayyy less than 275 or 475. grinning smiley

I've never had the problems reported by others in using DOT 5 in my non-abs cars that I have overhauled brake systems upon. I do not race, so that is a whole different animal in brake response! Plus, who leaves a race car brake system undisturbed for 3 years or more? winking smiley No need for DOT 5 for that application.

I also live near sea level. Within a day's drive I can hardly top 4000 feet.

Frank DuVal

Fredericksburg, VA

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Re: Silicone brake fluid revisited
Posted by: Frank DuVal ()
Date: December 17, 2017 10:59AM

Most all brake systems since the 50s have sealed master cylinders. I have never seen any evidence of moisture in the DOT 5 systems I have worked on. Of course, since they (DOT 5 filled) never fail the way DOT 3 does (stuck wheel cylinders and master cylinders with white corrosion), I have opened very few DOT 5 systems!

YMMV

Frank DuVal

Fredericksburg, VA

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Re: Silicone brake fluid revisited
Posted by: joelsplace ()
Date: December 17, 2017 11:21AM

A lot of Corvairs don't have sealed master cylinders. It seems to be random if the gasket sealed or not but that is probably from lots of replacements being different. I have seen a lot that weren't sealed. Mostly '63 and earlier.
Anyone know what came stock? IIRC the ones retained with the bolt weren't sealed and the bails were.



Edited 1 time(s). Last edit at 12/17/2017 11:22AM by joelsplace.

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Re: Silicone brake fluid revisited
Posted by: Seth Emerson ()
Date: December 17, 2017 11:34AM

Here is a good link to "up to date" info on brake fluids: [www.stoptech.com]


Note the reference to DOT 5.1 fluid (it is kind of buried in there)

Seth Emerson

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

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Re: Silicone brake fluid revisited
Posted by: Pedigo ()
Date: December 17, 2017 11:34AM

I opened-up my '61 Loadside after almost three decade's of neglect.
It was horrifying!
The corrosion of DOT3 and time wore out everything excluding the slave cylinder bores.I was lucky and able to rehone them within spec.
The master and all lines were toast.
Too much funk in the master and lines hold secrets.
The same secrets will get you killed.

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Re: Silicone brake fluid revisited
Posted by: Frank DuVal ()
Date: December 17, 2017 04:09PM

Pedigo, thumbs up

Frank DuVal

Fredericksburg, VA

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