Need advice about silicone brake fluid

[Guest]

I,m rebuilding my 67 disc brakes and a friend said use silicone fluid when I do.My parts store does not even carry it any more because of all the problens with it.Ameritech spent a lot of money to change over all their vechicles and then changed them back to reg.fluid.I dont believe any auto manufacturers use it.Help me decide about what to do. Thanks

[Guest John Chapman]

Norb,<P>Something to be cautious about... silicone-based and glycol-based brake fluids are NOT COMPATIBLE! More discussion below.<P>Wardy,<BR>You may have access to a different formulation of fluid(s) in the UK. See discussion in the link below to the Vintage Triumph site.<P>Discussion of brake fluids, including the new DOT 5.1 here:<BR> <A HREF="http://www.vtr.org/maintain/brake-fluids.html" TARGET=_blank>http://www.vtr.org/maintain/brake-fluids.html</A> <P>Here's a link on BCA with discussion about brake fluids: <A HREF="http://www.aaca.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=2&t=002430" TARGET=_blank>http://www.aaca.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=2&t=002430</A> <P>From there, here's the discussion:<P>"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:<P>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.<P>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.<P>The two fluids are absolutely incompatable. Changing requires a complete flush of the brake system and related components.<P>2. Both fluid bases have their strong points:<P>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.<P>Glycol: Inexpensive, readily available, will last a long time. Very serviceable in all but the most intense braking applications.<P>3. Both fluid bases have their Achille's heels, it's up to you to choose the least offensive relative to the strong points:<P>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.<P>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.<P>In my opinion, for street use, a well-maintained glycol-based fluid system is superior in servicablility to a silicone fluid system."<P>Cheers,<BR>John<p>[ 06-14-2002: Message edited by: John Chapman ]

[The Old Guy]

I have used DOT3-4 fluids for years and never had a problem. Many of the older cars that were switched to silicone fluid have experienced brake light switch failures. The hydraulic switches ,after two or three years stop working,and you do not know it has happened until someone smacks you ,and tells you that you have no stop lights.My 40 Buick has never failed me in thirty years,and I use the "old" stuff.

[Guest]

Many thanks to all who have replied.I will think it over and decide which to use.Probly not change at this time because I am only doing one side.I have rebuilt both front discs twice in 10 years and it is the worst job on a car.

[BUICK RACER]

Just some old common sense, sez not to use the new brake fluid, I was going to put it in my '73 Vette and never got around to it because it didn't seem necessary, the old "stuff" absorbs water and hence causes rust, but the only reason it absorbs moisture is if it is open to the elements, so if the brake system is closed, not rusty or whatever way it could get moisture, it is going to work just as good, or better in aimost all cases than the silicone or synthenic, same theory for the R12 vs R134 in the AC!

[Guest]

When I was in Automotive Brakes class my instructor noted that silicon can leak out of calipers and other seals in old cars because it is thinner than the "old" stuff. The original system was not designed for silicon fluid. <P>If everything is new or rebuilt to close tolerances it should be ok.

[Guest trevor ward]

oldgsnut......,<P> what exactly are the "problems" that you are aware of ??. I restored a v.w. bug a few years ago which was an absolute every last nut and bolt job, and went for silicon 'cos it will not harm paint at all so any spills are not a problem also a much better "pedal" is obtainable as once you have a good set up it does not absorb moisture so you don't end up with a spongy pedal, ( other probs. aside , such as leaks e.t.c. <BR> Also. the product i used was also compatible with regular fluid, but i cannot see the point in mixing the two, as it kinda would defeat the object somewhat!! so unless i am missing something, i cannot see any down sides, but maybe somebody will come back and say your nuts will drop off after a few years use <P> hope this is of some use......<BR> WARDY..............<P><BR> <B>'64 LE SABRE ........DONE??!</B>

[NTX5467]

The original magazine articles I saw on the original Dow-Corning silicone brake fluid sounded very promising--expecially in the parts of the world where temperature extremes were common (which would cause moisture to form int he system from condensation that would not be cooked out with use). At that time, they stated that you could mix it with conventional fluids and it would work ok, but if the vehicle did not see use for a while, the two fluids would separate out, yet still work. This was in the later 1970s.<P>A friend then acquired a '79 Corvette and we'd all heard about the massive costs to rebuild those 4 piston caliper Corvette brake systems (due to moisture issues, typically). He decided to change the Corvette over to silicone fluid as it was a DOT5 fluid. Local auto supplies did not carry it and he finally found some at the motorcycle shops (even in various brands).<P>He bought enough fluid and completely bled the system on the Corvette. He did notice a slightly spongier pedal for about a week and then it got very firm and consistent (must have been a little air that finally made its way to the top with time and use). No problems with the brakes at all, as I recall.<P>At that time, silicone brake fluid was in the same somewhat exotic orientation as synthetic motor oil, mainly due to cost issues and the fact that you had to get outside of the normal supply chain to find it.<P>I believe the theory behind silicone fluid is good, but only for systems that are reasonably new and well maintained.<P>Using a high quality brake fluid of the highest DOT spec number is a very good investment, from a closed container hopefully, but remember how the gallons of brake fluid at the old service station were always open? <P>Considering the higher level of performance of current brake fluids (compared to earlier versions), to me the reality is that unless you are in a situation where you need the extra performance of silicone fluid (not related to maintenance issues), the current DOT 4 fluid will work just fine and be compatible with all of the seals and such in the system.<P>Just some thoughts . . .<BR>NTX5467

[Guest]

i'm using Silicone in my 56 Packard for over 4 years and 10K miles now. I have determined NO advers affects othe than cost of the silicone brake fluid. Its running about $25/qt at Napa auto parts. Even more expensive at AAP discount. I run this car pretty hard on open hi-way and Interstate driving. This is my first experience with the silicone, but so far so good.