Stuart :
I disagree with you on most points. I've used silicone fluid in my TR3 for
over 15 years, and I like it so well I've converted my other cars and
motorhome as well. Using the factory glycol, my Chevy needed it's first
wheel cylinder rebuild at only 60,000 miles. I switched it to silicone at
the time, and it is still using the original seals on the other wheels and
M/C at around 200,000 miles, with no further attention. About 6 years ago,
I mistakenly rebuilt the rear wheel cylinders on the TR3 (the actual
problem turned out to be the flexible line to the rear axle), and found the
cylinders remarkably clean and free of corrosion.
See below for more rebuttal.
Randall
On Tuesday, March 23, 1999 10:52 AM, Stuart Steele
[SMTP:ssteele@switchsolutions.com] wrote:
> Drawbacks
> 1. ) Very hard to pour without entraining air bubbles - hence an
> application will generally have a softer, spongier pedal feel
Not difficult at all, just something to be aware of. Holding a clean
screwdriver across the end of the can for the fluid to run down works just
fine if you are doing an initial fill. Not a problem if you are just
'topping off', since the bubbles will come out in the M/C.
> 2.) Doesn't absorb water - any water in the system accumulates
> in the lowest point of the system and stays there, concentrating rust
Yes, but with silicone fluid there will be no water in the system to begin
with. UNLIKE glycol fluids which actually suck water out of the air, and
then let it condense in the system under temperature changes.
> 3.) Whereas glycol fluids begin to compress near their boiling
> points, silicone fluids begin to compress at around 300 to 350 degrees
> Fahrenheit.
Since this is above the boiling point of glycol, it hardly seems relevant.
I'd much rather have a soft pedal than no pedal !
> 4.) Additives in the fluid can vaporize at comparatively
> moderate temperature, increasing the spongy feel.
If they vaporize at less than 350 deg F, then the fluid is not DOT-5 ! See
above.
> 5.) Silicone fluids expand significantly when hot.
Which is only a problem under some very strange circumstances.
> 6.) Functionally incompatible with systems which have held
> glycol-based fluids for any length of time, requiring flushing and seal
> replacement( Note that there are counter opinions on this that state
> that the modern silicone formulations are in fact compatible with only a
> flushing, rather than a complete reseal. ) The actual DOT specification
> requires chemical compatibility, so as far as that goes, the two fluids
> won't cause reactions if used in the same system, but they certainly
> won't mix, either.
I mixed the two on my motor home some 10 years ago, without even thoroughly
flushing the system. The glycol eventually formed a thick black sludge,
which had to be cleaned from only one slave cylinder. All others are still
working fine. I did not replace seals on any of my vehicles, and have not
replaced a wornout seal since (except the clutch slave on the TR3, which
was a special case). The motorhome slave with the sludge problem actually
quit leaking after cleaning and reinstalling the old seal.
> 7.) Functionally incompatible with anti-lock brakes. In the
> first place, the silicone fluids tend to be more viscous, which can
> cause problems with the timing of the pulses, which are intended to work
> with the thinner glycol-base fluid. This sometimes leads to damage to
> the ABS valving. Secondly, the rapid pulsing necessary to anti-lock
> function tends to cause cavitation in the fluid, as the tiny bubbles
> collapse and coalesce into larger ones, and then collapse and reform
> into smaller ones. This tends to nullify the ABS effect, can diminish
> the actual effective braking to a dangerously low level, heats the fluid
> leading to further sponginess, and can damage the ABS controller.
I find this VERY difficult to believe, since glycol is actually THICKER
than silicone at low temperatures.
> Thirdly, silicone brake fluid tends to foam when expressed from a small
> orifice under pressure. This, of course, reduces its hydraulic
> effectiveness to nothing in the area affected.
Only in the presence of air. Air in hydraulic brakes is a no-no anyway.
> 8.) The silicone tends to attract and bind with the fragmentary
> wear products of the rubber components in the brake system, creating a
> gelatinous sludge, which can block fine passages, particularly in ABS
> systems.
My experience is that glycol fluids are much worse about this than
silicone. The big problem is when you don't get all the glycol out when
switching to silicone. In this case, the glycol goes on absorbing water
and deteriorating, forming pockets of sludge.
>
>
> Having dispensed with these generalities, let us turn to Steve's
> particular questions:
>
> > <<I would suggest using DOT 5 silicone brake fluid. It is very high
> > temperature (won't boil under extreme use), does NOT absorb
> > water, and is
> > completely compatible with DOT 3 or DOT 4 brake fluids.
>
> ( Grudgingly tolerant of, is more like it - ed. )
>
> > It is best to completely replace the existing fluid with
> > DOT 5 but not
> > necessary.
>
>
> This is patently not so, at least not for straight silicone brake fluid.
I did it, it worked OK for me.
> The two fluids are immiscible, and have different densities - one floats
> on the other. There is some talk of a silicon ester-based fluid, with a
> boiling point of 590 degrees Fahrenheit, which is miscible with
> glycol-based fluids, but I don't think that any of these are
> commercially available.
>
> > DOT 5 is expensive compared to DOT 3 or DOT 4. But you can
> > forget period
> > flushing of lines, rust in lines, wheel/master cylinders, etc.>>
>
> This, also, is both false and unwise - moisture is still absorbed into
> the brake system through the seals at the same rate, only instead of
> being held in suspension, accumulates in huge globules. This tends to
> accelerate local corrosion, and should that large globule of water ever
> boil, could easily dangerously compromise braking almost
> instantaneously.
NOT SO ! The primary entry of moisture is by being absorbed from the air
by glycol. My personal observation is that glycol fluid causes much more
corrosion than silicone, especially if you don't periodically change it.
>
> >
> > There has been much discussion as to brake fluid, biennial
> > changing of brake
> > fluid, brake system fluid compatibility, etc.
> >
> > Is DOT 5 suitable for use in (our) more conventional MB's?
>
> No.
>
> > Is it compatible
> > with the DOT 4 in them now?
>
> No. Chemically, mixing the two will not create a third, explosive or
> acidic or otherwise harmful compound, but functionally they do not get
> along.
>
> > Will it reduce maintenance as described in the
> > last quoted paragraph?
>
> No. One still must replace the fluid periodically to flush the
> gelatinous rubber-dust slime and the occasional lurking water bolus.
>
Here again, my personal experience contradicts this. I haven't changed
fluid periodically for many years, and have had no problems.
> > Has anybody used/switched to DOT 5
> > in their cars,
> > other than Mogs, and how did it work out.
>
>
> I have read of the experiences of a number of members of my Triumph list
> who have gone to silicone brake fluid - other than flushing and
> resealing the system, and the seemingly permanently slightly spongy
> pedal, most reported that they were satisfied. One very real issue with
> these cars is that the seals are often not what they could be in the
> brake and clutch master cylinders in the first place, and _every_ owner
> has stories of leaking MC seals destroying the paint on the firewall, so
> this aspect represents a very real value. Also, these are often weekend
> cars, for pleasure driving only, so many don't see a lot of brake system
> heat.
>
Well, this Triumph lister did not 'reseal' the system, and I frequently
drive my TR3A quite hard. My little experience with the internally blocked
flexible line actually caused the paint to blister on the rear wheels,
which just might count as 'a lot of brake system heat'.
>
> > Remember, a lot of the time, the maintenance instructions
> > and schedules
> > presented with the car represent the technology at the time
> > that it was
> > produced, and the introduction of new materials, chemicals
> > and oils may render
> > the original recommended service intervals obsolete. MB
> > probably does know
> > best about their products, but they print owners manuals
> > for the car during
> > the year of its production, and don't update or modify
> > these schedules when
> > new products are introduced.
>
> I do not think that this is the case with brake fluids. Further,
> Mercedes periodically updates their fluid specifications.
>
> Having torn silicone fluid down, who uses silicone fluid then? The sole
> major user, to my knowledge, is US Government, mainly the armed forces,
> although the Post Office is a big user, too. They use it because it is
> stable and predictable over a wider range of temperatures, has a high
> boiling point, and doesn't absorb moisture. ( It does not appear whether
> the government cares about the paint issue. ) I can find no evidence of
> any other major benefits that the government expects from the silicone
> fluid.
Let's see. Lower maintenance, longer life, predictable higher performance
under all conditions. Specified by one of the largest consumers of custom
made motor vehicles in the world. On top of that, it doesn't eat paint.
Takes a lot to convince you, huh ?
>
>
> Stuart Steele
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