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Silicon brake fluid
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ram300
Posted 2020-04-15 5:10 PM (#596885)
Subject: Silicon brake fluid



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I'm curious to find out what FWDLKers experiences with silicon brake fluid are. I've recently fully gone through my 57 NYers brake system, a factory nonpower brake car, I've replaced absolutely everything so it's a perfect time to add silicon fluid. I've already run it in a couple of my other cars which I must admit don't get much mileage put on them, it seems excellent for cars that sit around a lot. No corrosion, no leaky wheel cylinders etc etc. The only possible down side I have noticed is a slighty more vague/squishy pedal feel, I've been told this can be due to the fact that silicon fluid is a lot harder to bleed all the air from the system than standard fluid. Anyway the '57 NYer I'm planning to use it on will have much more regular use and I'd like to hear practical insight from guys/girls that have run the slicon fluid in the FWDLK cars for sometime and used them regularly. I've seem some negative remarks on various other forums but most unsubstantiated rumours. Also I'm not going racing so I'm not after feedback regarding stopping repeatedly at 150+mph, just everyday normal driving.

Thanks
Owen
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finsruskw
Posted 2020-04-15 8:29 PM (#596893 - in reply to #596885)
Subject: Re: Silicon brake fluid



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Plan on a mechanical brake light switch mod.
Silicone will eat the OEM hydraulic switches and before you know it you will be running around w/no brake lights!
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1957sotos
Posted 2020-04-15 9:14 PM (#596900 - in reply to #596885)
Subject: RE: Silicon brake fluid


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I run silicone in my 57 with power brakes about ten years now, and only had to top off once. With the booster on top of the master, inspection is difficult, hence reason
for using it. However, the pedal rides lower and after three brake light switches failing, rigged a mechanical switch.
My other 57 has manual brakes, so is much easier to top off (about every spring). It has a good firm high pedal and has the original (guessing) brake light switch.

Perry
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ram300
Posted 2020-04-15 10:03 PM (#596905 - in reply to #596900)
Subject: RE: Silicon brake fluid



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Yes I did have a brake light switch leak also on my other car and it was a fairly simple fix with some two pack expoxy around the brake light pins it's never leaked again. 2 or 3 years on.....



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1960fury
Posted 2020-04-16 6:02 AM (#596915 - in reply to #596885)
Subject: Re: Silicon brake fluid



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Tried it many years ago, late 80s/early 90s. All the rubber in the system that got in contact with the fluid went bad after a few weeks. I must add I just changed the fluid and not the seals, the seals were old, maybe OE.
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58coronet
Posted 2020-04-16 7:56 AM (#596918 - in reply to #596885)
Subject: Re: Silicon brake fluid


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I rebuilt the entire brake system in my 1958 Coronet in 1990 and filled with silicone fluid. Never had anything apart since, have driven it approximately 10,000 miles in the last 30 years and have never had a leak or problem with the brakes since the rebuild.
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big m
Posted 2020-04-16 11:31 AM (#596927 - in reply to #596885)
Subject: Re: Silicon brake fluid



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Only way to go.

I Let my '58 Dodge set nearly ten years without use, and brakes were just like new when I got the car back on the road. No grabbing, pulling, etc. that is a byproduct of conventional fluid drawing moisture in from the air.

A mechanical brake light switch from an early sixties Chrysler is easy to install beneath the dash, and eliminates the pressure switch.

---John
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wizard
Posted 2020-04-16 12:51 PM (#596929 - in reply to #596885)
Subject: Re: Silicon brake fluid



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DOT5 should never be mixed with any other brake fluid, not even residue. The best thing is to open all wheel cyliders, wash them out and blow alcohol throgh the brake tubes.

The worst thing is if there is DOT4 or residues of DOT4 in the brake system - it can turn to mush which may effect rubber seals
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57chizler
Posted 2020-04-16 2:34 PM (#596937 - in reply to #596929)
Subject: Re: Silicon brake fluid



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Richard Ehrenberg, a well-known Mopar guru and a member of the SAE wrote this concerning the mixing of brake fluids:

"Tech Question
Gary Boak, Chilliwack, BC, Canada, 1969 Dart Swinger 340

I notice in the April 04 issue you say that DOT 5 brake fluid can be used without flushing the system. Everything I have heard and read states that Dot 5 does not mix with anything except DOT 5. When switching to DOT 5 are you not supposed to use new rubber?

Gary-

Another old wive's tale. First, realize that DOT specs don't specify the composition of the fluid, the rating relates only to the boiling point. So, therefore, it would be possible to have DOT 3 fluid that's silicone, and DOT 5 that's not (and this latter combination does exist.) These specs are covered in detail in Federal Motor Vehicle Safety Standard section number 571.116, which is part of the Code of Federal Regulations, #49, Chapter V, see for yourself at:

Code of Federal Regulations, #49, Chapter V
Here's an excerpt from the law on boiling points:

Equilibrium reflux point (ERBP). When brake fluid is tested according to S6.1, the ERBP shall not be less than the following value for the grade indicated:

(a) DOT 3: 205 °C. (401 °F.).

(b) DOT 4: 230 °C. (446 °F.).

(c) DOT 5: 260 °C. (500 °F.).

A recent change to the law specifies that non-silicone fluid meeting DOT 5 temperature specs. be labeled DOT 5.1. All DOT 5 fluid must be purple in color, all other grades must be clear to amber.

The baziilion pages of the specs relate mostly to boiling points, viscosity, and the fluid's effects on rubber (swelling), as well as testing procedures. But there's also much written about compatibility. What has probably caused the confusion is that DOT 5 fluids are tested differently than other types, but these tests apply equally to silicone and non-silicone fluids. Subchapter S6.5.4 addresses miscibilty, specifying that the fluid being tested must mix with a standard type fluid, and this miscibilty test DOES apply to DOT 5 fluids, and can't gel, swell cups, etc. when mixed. So there!

The Society of Automotive Engineers (SAE) also has detailed specs: J1703 and J1705.

It's true that much has be written saying that silicone based fluids cannot or should no be mixed with other types, this is that old myth-perpetuating deal. Nowhere can I find a scientific study or analysis to back this story up - do a Google search yourself if you don't trust me.. There's only been two studies on this that I'm aware of: Dow-Corning, the leader in silicone brake fluids (possibly the only true USA manufacturer), did a detailed study almost 30 years ago, wherein a system was haphazardly swapped from DOT 3 to silicone, with the intent of leaving a significant portion of the fluid Unchanged. The system passed all DOT tests easily. The second test is less scientific, but, to me, more significant: Yours truly has been using DOT 5 silicone in every car I've owned or serviced since approx. 1978. I have never flushed a system! I have, in some cases, bled out most of the old stuff, in other cases, I've just topped up a DOT 3-filled system with silicone. Cars serviced by me in this fashion have stopped will from speeds over 160 MPH. I've never had a stuck caliper (or wheel cylinder) pistion since making this change universal in my fleet - even in cars stored for long periods. I've also never damaged pain from a brake fluid spill. Come to my garage - you will find 4 or 5 bottles of DOT 5 silicone, and zero of DOT 3 or 4.

On your Dart, do what I do (and say): bleed out as much of the old garbage as you can, until you see purple at each bleeder screw. And don't worry about it!

End of story."
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wizard
Posted 2020-04-16 4:00 PM (#596948 - in reply to #596885)
Subject: Re: Silicon brake fluid



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Thanks' John, very interesting and logic in the sence that if someone mixed different fluids unintentional the veheicle should still function and no damage to rubber parts, BUT.

There's always a but I do beleive that Sid had the problems he describes since I personally know other classic car owners with the same experiance.

A friend had to change every rubber part in his Mercedes after having tried the DOT5 - Everything turned to mush.

I also know some guys that just sucked up all DOT 3 in the m/c and filled up with DOT5, and then bleed out the system until Purple fluid came out - no problems.

So, is there anyone that have a plausible explanation for this?
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1960fury
Posted 2020-04-16 4:29 PM (#596949 - in reply to #596948)
Subject: Re: Silicon brake fluid



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wizard - 2020-04-16 4:00 PM

Thanks' John, very interesting and logic in the sence that if someone mixed different fluids unintentional the veheicle should still function and no damage to rubber parts, BUT.

There's always a but I do beleive that Sid had the problems he describes since I personally know other classic car owners with the same experiance.



Yes, back then I was driving daily and the sudden failure after the switch couldn't have been a coincidence, I had no problems before. All the rubber seals had swolen up almost twice the original size. At least that is how I remember it (30 years!). Of course I flushed the system even tough this wasn't recomended in the instructions, yet, as you say, the residue (or the regular brake fluid soaked in the 30?yo seals?) was enough to lead to a VERY spongy/leaking brake system with almost zero brake action.
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1960fury
Posted 2020-04-16 4:34 PM (#596950 - in reply to #596937)
Subject: Re: Silicon brake fluid



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57chizler - 2020-04-16 2:34 PM

Richard Ehrenberg, a well-known Mopar guru and a member of the SAE wrote this concerning the mixing of brake fluids:


............A recent change to the law specifies that non-silicone fluid meeting DOT 5 temperature specs. be labeled DOT 5.1. All DOT 5 fluid must be purple in color, all other grades must be clear to amber.............



I wonder what was the reason behind this law....
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wizard
Posted 2020-04-17 1:08 AM (#596982 - in reply to #596885)
Subject: Re: Silicon brake fluid



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I made a test with Old Wheel cylinder seals from 58, submerged in dot5 for more than a month and there was absolutely no swelling or mushy rubber. This test was done before I changed to dot5.

Still I'm very curious why some have problems while others don't
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60 dart
Posted 2020-04-17 4:38 AM (#596986 - in reply to #596885)
Subject: Re: Silicon brake fluid



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it's not advisable to mix the 2 because the dot 5 will lose it's water repelling characteristics . other than that it can be mixed . been there done that! -----------------------------------------------------later
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57plybel
Posted 2020-04-17 9:08 AM (#596990 - in reply to #596885)
Subject: RE: Silicon brake fluid



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Ran it for 15+ years after full stock rebuild. No leaks and maybe 1x 20ml top up in those 15 years..... flushed it all out with new fluid late last year; fluid was still very purple in colour with no discolouration from the black rubber.... very happy with the performance over 10,000 miles .

On the inside of one of the front tyres, there has always been a very light haze / film which has been determined to be caused by casting porosity of one of the wheel cylinders....no real problem. 

And it ate the existing pressure switch and a NOS one soon after..... mechanical switch on pedal box gave far better advance warning to following cars.....

Not always easy to obtain, so best keep some spare....

 

Colin

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57chizler
Posted 2020-04-17 1:24 PM (#597006 - in reply to #596948)
Subject: Re: Silicon brake fluid



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wizard - 2020-04-16 1:00 PM

Thanks' John, very interesting and logic in the sence that if someone mixed different fluids unintentional the veheicle should still function and no damage to rubber parts, BUT.

There's always a but I do beleive that Sid had the problems he describes since I personally know other classic car owners with the same experiance.

A friend had to change every rubber part in his Mercedes after having tried the DOT5 - Everything turned to mush.

I also know some guys that just sucked up all DOT 3 in the m/c and filled up with DOT5, and then bleed out the system until Purple fluid came out - no problems.

So, is there anyone that have a plausible explanation for this?


Engineering data versus anecdotal experience. Anecdotal experience varies.

Long before there was silicone fluid I saw lots of brake hydraulic systems full of sludge; so, when there are reports of sludge after mixing silicone/glycol fluids, who knows if the sludge wasn't forming before the mixing.

There is a known incompatibility between some fluids and some brake components; for example, the Brits used Girling fluid for many years and other fluids would attack the rubber in Girling systems.

In the article above, one of the key words is "miscible", this means that two substances don't "mix", they simply separate when combined. The pic below is a "mix" of DOT 3 and DOT 5; as can be seen, they separate into distinct layers.

As to brake light switches failing, many recommend the use of Harley-Davidson and some report that even those fail with silicone. Well, I just sold my 2005 Harley and the brake lights were still working fine after 15+ years of exposure to silicone fluid.

This illustrates the value or not of anecdotal experience.



(Silicone mix 02.jpg)



Attachments
----------------
Attachments Silicone mix 02.jpg (65KB - 19 downloads)
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57chizler
Posted 2020-04-17 1:28 PM (#597007 - in reply to #596950)
Subject: Re: Silicon brake fluid



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1960fury - 2020-04-16 1:34 PM

57chizler - 2020-04-16 2:34 PM

Richard Ehrenberg, a well-known Mopar guru and a member of the SAE wrote this concerning the mixing of brake fluids:


............A recent change to the law specifies that non-silicone fluid meeting DOT 5 temperature specs. be labeled DOT 5.1. All DOT 5 fluid must be purple in color, all other grades must be clear to amber.............



I wonder what was the reason behind this law....


As stated, glycol fluid attacks paint and some plastics, silicone is more benign.
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wizard
Posted 2020-04-17 4:00 PM (#597013 - in reply to #596885)
Subject: Re: Silicon brake fluid



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Thanks' John - yes, you're right, it's one plausible explanation that there was sludge in the system before the DOT5 was poured in.
Since that DOT3 is hygroscopic there will be a lot of sludge and gunk if the brake fluid is not exchanged periodically.
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51coronet
Posted 2020-04-24 6:54 PM (#597303 - in reply to #596885)
Subject: Re: Silicon brake fluid


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I use it however its a pain to bleed and will take a few days to properly bleed it. Silicon fluid will form very tiny air bubbles and hold them suspended in the fluid for long periods of time. Speaking from experience with DOT5 be diligent and bleed the system more than once and let plenty of time pass between the bleeding. If you look close enough you will see and feel what I am talking about.
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Mike M
Posted 2020-05-06 10:27 AM (#597860 - in reply to #596885)
Subject: Re: Silicon brake fluid



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I rebuilt the brakes on my Fury back in 1985 using silicon fluid. The car basically sat until 2007 when I finished it to go to Tulsa. I bled the brakes 1n 2007 again using silicon.
So far I have had no problems.
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22mafeja
Posted 2020-05-21 1:28 PM (#598586 - in reply to #597860)
Subject: Re: Silicon brake fluid


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I love the silicone because it :
Won`t eat the paint , I have never assembled new tubes and master cylinder without major spillage on the frame and firewall.
The cylinders will be as new after 15 years or so-try that with DOT3-4-nope

Of course you can only fill the system with silicone fluid when EVERY rubber component is new...
The only problem I have noticed with silicone is that it will be darned hard to get the tubes nipples leak free.
The pedal might be a little softer but not much.
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