Silicone brake fluid

[Judd]

Y'all

I've decided to rebuild all the wheel and master cylinders on my 56 Special with power brakes. How would I go about changing to silicone brake fluid? Thanks.

Judd

[The Old Guy]

If you completly fush the system you should have no problem, but why do it? The silicone fluid will put you in a position where you will never know when your stop lights will not work. If you do put the silicone fluid in, PLEASE carry an extra stop light switch, as you will need it.

[Guest imported_56BuickSuper]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">If you completly fush the system you should have no problem, but why do it? The silicone fluid will put you in a position where you will never know when your stop lights will not work. If you do put the silicone fluid in, PLEASE carry an extra stop light switch, as you will need it. </div></div>

Why is this? Please provide more details.

Dan

[Guest Teamsterdug]

From time to time this subject arises on the DF. It's a good topic to bring up once in a while though. The silicone brake fluid seems to have an adverse affect on the brake light switches for some reason. I've used silicone on two different Buicks ('38 & '53) and have found that the switch does indeed only last about a year. It's an easy fix though and new switches are readily available so no big deal. I guess it depends on how strongly you feel about the attributes of silicone vs regular brake fluid. I'm no expert but have used the silicone because it is supposed to be more immune to picking up moisture from within the brake line system. Just recently, when I pulled the wheels on my '66 (a very low mileage car that apparently sat idle a long time) to check and repack bearings I found that the wheel cylinders were leaking a nasty rusty looking goo. I'm in the process of replacing all of the wheel cylinders now and most likely will switch over to silicone on this car too. I can't help but think that the entire system has been contaminated with this rusty stuff. Even if there is only a trace it is not a good thing and should be corrected.

[Guest Albert]

I have heard the same thing about the switches going bad, mine has been filled with dot5 now for 2 years and no problems as yet but my system was all new before it was fill, also dot5 does not seem to swell the rubber as much as the Dot 3&4 does. If the switch does go i would be tempted to install a mechanical switch.

[Guest Skyking]

What is the best way to flush an old system??

[Guest]

1st - the best way to flush a system is to replace all brake components including lines, in other words, a complete brake restoration. DOT 3 is the basic brake fluid that is intalled even in new vehicles. This has the lowest boiling point and is the least expensive. In newer vehicles we see little leakage at seal points for a long time. DOT 4 is a refined DOT 3 that has a higher boiling point and slighly less moisture absorption properties. Both DOT 3 and DOT 4 will absorb mositure from the air and eventually this combination becomes acidic and deteriorates wheel cylinders, etc causing leaks and more air to fluid absorption.

Silicone brake fluid is non hygroscopic and therefore is considered the best choice for old car hobbyists whose cars sit for long period of time. I don't know anything about the brake light switch issue, first I have ever ehard of that but it sounds valid if others have experienced this concern.

My choice would be DOT 4 with an annual brake flush. Here is why. If you find yourself on a tour and develop a leak in the brake system and pull over to get Silicone brake lfuid you may be out of luck and YOU ABSOLUTELY CAN NOT MIX DOT 3/4 AND SILICONE. That is why manufacturers do not use synthetic. They don't want some Jiffy Lube shop toping off their synthetic fluid with DOT 3 then paying for the new warranty claim.

Keeping fresh, readily available fluid in my hydraulic brake system appeals to me much more then using the more expensive less available Silicone fluid. Try using DOT 4 and flushing your system every fall before your cars are put away. This means buying about 1 1/2 quart of DOT 4 at your local NAPA or such and running it all through the system - using it all up. Then you will have fresh brake fluid at the brake cylinder seals that will easily last a year - all for the cost of about $6.00. Tighten the master cylinder cap tight and your all set.

As for flushing a system that has DOT 3 in it and using Silicone - first I would push out as much of the old as possible by using the assistant-at-the-steering wheel method. I would add some purple food dye to the Silicone fluid - just enough to be able to tell the difference between DOT 3 and Silicone when it comes through at the wheels - and fill and push until only purple hued brake fluid comes through. Then run regular silicone (non dyed) through until normal color is attained. (Some Silicone fluid is already a different color so people won't mix with DOT 3)

Hope this helps.

Bryan Moran

"Wildcatr"

1961 Electra 2 door hardtop

1964 Wildcat convertible

1972 Limited

ASE Master Technician / Mazda Master Technician / Subaru Certified Technician

[Guest imported_NikeAjax]

Wow, to think some of you have gotten a whole year out of hydraulic-switch and silicone brake fluid mix! I tried this once, on both of my cars, my 1959 Rambler American and my 1956 Century, the switches are identical too, but for some reason, the Rambler's NEW switch would only last two weeks tops, but sometimes would last only one day, I can't say for the Buick, it was waiting for lots of work in the garage, so it wasn't driven. It's rather embarrassing having a city buss pull up next to you and tell you your brake-lights don't work, "Aw f**king-sh*t!" Then you pray you don't get rear-ended on the way home 'cause the person in back of you isn't watching your lights, but fascinated at seeing such a nice old car! I have found that the braking is inconsistent in silicone too, sometimes it feels mushy, other times, it feels like a rock; I had a new brake system too, and no bubbles either.

[Judd]

Thanks for the info! I guess I'll just use the DOT4. We can drive our cars all year round down here in south Mississippi should we still flush the system every year? Thanks.

Judd

[Guest Skyking]

Same with me....I keep the DOT 3 in.....I'll try silicone in my hydraulic clutch system in the Met.......

[Guest John Chapman]

Judd,

There's no free lunch with either fluid. Glycol based fluid should be changed at least every three years, because it absorbs moisture from the air. The more humid the climate, the faster the build up. It's been documented that after three years, up to 30% of the 'fluid' can ber plain old water.

Here's a bit of a post I did about two years ago. Hope there's some info that you can use:

Discussion of brake fluids, including the new DOT 5.1 here:

http://www.vtr.org/maintain/brake-fluids.html

Here's a link on BCA with discussion about brake fluids: http://www.aaca.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=2&t=002430

From there, here's the discussion:

"I'd carefully consider any change in brake fluid. The I've got a lot of research that I can provide you via separate email if you're interested, but the salient points are:

1. The designations of DOT 3, DOT 4 and DOT 5 are based on the dry/wet boiling point of the fluid, not whether it is glycol-based or silicone-based.

In the US, the only DOT 5 fluid marketed is silicone-based, hence the general misconception that DOT 5 is only silicone. Glycol-based DOT 5 is available in much of Europe, Africa and Asia.

The two fluids are absolutely incompatable. Changing requires a complete flush of the brake system and related components.

2. Both fluid bases have their strong points:

Silicone: Isn't hydroscopic (won't absorb moisture), so corrosion of interior components isn't likely. As a DOT 5 fluid, has a high boiling point (important if you're doing heavy duty braking. It won't harm automotive finishes.

Glycol: Inexpensive, readily available, will last a long time. Very serviceable in all but the most intense braking applications.

3. Both fluid bases have their Achille's heels, it's up to you to choose the least offensive relative to the strong points:

Silicone: Has tendancy to aeriate (absorb airbubbles) during installation and over time resulting in soft pedal feel. Requires a complete system overhaul/flush to install. In routine street use, annual replacement is recommended. Difficult to bleed air out of system.

Glycol: Absorbs water. Estimates for absorbtion rate average about 5%/year in total volume. Rate is higher in humid climates. Water can turn to vapor (steam) under heavy use causing soft pedal and loss of braking ability. Water can condense in lines and freeze causing braking difficulties. Water can cause internal component corrosion and failure. Ruins painted surfaces. Conservatively, should be replaced a every three years.

In my opinion, for street use, a well-maintained glycol-based fluid system is superior in servicablility to a silicone fluid system."

Cheers,

John

[Guest imported_56BuickSuper]

Just so I can learn a bit more. What happens if you mix dot 3 and dot 5. I mean if your system is dot three and you add dot 5 to top off, or all of the dot 3 is not flushed out when replacing with dot 5. What would or could happen. Or, lets say you purchased an older car that had been converted to dot 5 and you did not know and added dot 3. What would be the tell tail signs?

Dan

[Guest John Chapman]

Dan,

That depends...

Keeping in mind that the DOT rating is independent of the type of fluid and relates only to the dry/wet boiling point of the fluid.

As long as the fluid is either glycol- or silicone-based, adding more of the same based fluid of any DOT rating is OK. You'll just change the boiling point of the fluid depending on what DOT rating you've added.

The key point is: Glycol-based fluid and silicone-based fluid are [color:\\"red\\"]<span style="font-style: italic">completely incompatible</span>. Mixing the two will lead to brake system failure... sooner, rather than later. This is why when changing between the two fluids, it is essential to completely clean the system of the old fluid. This, in essence, requires a complete system tear down and rebuild to get the old fluid out of cylinders and lines.

Cheers,

John

[Guest]

I must be doing something wrong. I put silicone fluid in a '41 Cadillac in 1987 and the same stoplight switch is still in there working just fine.

What does the silicone do to the switches that causes them to fail? Are some switches better than others? Anybody know?

hvs

[Guest imported_NikeAjax]

The silicone, as much as I can tell, destroys the rubber membrane in the hydraulic switch. Perhaps you have one that is older and a different type of rubber, or is your switch mechanical?

[NTX5467]

I'll tend to agree that perhaps normal DOT3 or DOT4 fluid might be the best way out, especially considering the availability in the open market in non-metro areas. Doing the flush every so often might be a pain, but it tends to be inexpensive insurance. Another way to do the flush might be with a "power bleeder" setup or one of the manual pump brake bleeder setups that uses a hand pump with a hose that attaches to the bleeder screw.

As for the silicone fluid situation, back when silicone fluids first came out in the 1980s, DowCorning was the main source for it. It was billed as not absorbing moisture and was advocated for vehicles like Corvettes with had problems with their four piston caliper housings being pitted and needing replacement (which also led to the stainless steel sleeving operations too).

A friend had acquired a '79 Corvette in about 1981. He had heard of the caliper issues and investigated the silicone fluid as an alternative before things got to that point on his car. At that time, DowCorning (or someone of that nature) said that it was ok for the two fluids to mix as they would work ok without any problems. What did happen after a time of non-activity was that the two liquids would separate, but not react to each other. I recall seeing a picture in a glass jar of the two liquids. One picture showed the solution and the other one with the two liquids separated with one settling out to the bottom and the other one on top of it.

What my friend found for a source at that time was motorcycle shops as they had been using it for some time. It was also less expensive there than at the chain auto supplies (even though it took more small bottles of it). In more current times, sources might be some of the shops or vendors which supply and cater to SCCA autocrossers and racers. Possibly a copy of "Auto-X" magazine would have some ads for these people.

After doing the flushing routine, he noted that the pedal had a little more sponginess to it than previously, but after about a week of driving, it became more solid than before with a better feel in performance driving. We suspected that there might have been some air bubbles in the system that had worked their way out or something. End result, he was happy with the conversion.

Prior to that, we had used Castrol GT LMA (Low Moisture Avidity) brake fluid. Seems like it was DOT4. At that time and probably now, it's pretty well available and just a little bit more expensive than DOT3.

As for the higher heat toleranace of DOT4 than DOT3, for the normal driver that's probably not going to be a problem. GM still recommends DOT3 for Corvettes and the F-body cars (Camaro/Firebird). With the speed capabilities of those cars and the heat that can be put into the brake calipers during one of their top speed stops, if something else was needed, it would be there, I suspect.

As for the flushing every so often, that can probably also extend to the newer cars with their anti-lock brake systems. It's suspected that many of the same moisture issues might also affect these valves/modulators on vehicles that don't see very much driving at a time.

I'll admit that my information is somewhat dated compared to what the current recommendations might be (as to silicone fluid and mixing/flushing), but what I mentioned seemed to be pretty much the way it was when it first came out. When it first came out, it was supposed to be the "best" brake fluid with all of the good things and few of the bad things--plus at a hefty price back then. But, it kind of seems like buying a GM truck with G80 Locking Differential. It might cost several hundred dollars as an option, but if it saves you one tow bill, it's pretty much paid for itself.

Back when silicone fluid first came out in the 1980s, the main markets were supposed to be Corvettes, muscle cars, and other cars that saw little or sporadic use. No one considered that annual or similar flushing of the brake system with fresh fluid might be a cheaper alternative, from what I saw. It's also much easier to replace master cylinders and wheel cylinders than rebuild 4 calipers with 4 pistons/caliper or purchase new caliper assemblies.

Just some thoughts,

NTX5467