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Discussion Starter · #1 ·
Because I renewed the entire brake system I'm thinking of using silicon based brake fluid. I've found quite a bit positive stories about this stuff but are there any negative sides compared to the convential "paintstripper, moisture absorber" versions? If it was that much better then convential brake fluid, then why isn't every new car leaving the factory with it?
 

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I'll have to check my deleted folder, but I had a link to a discussion regarding the silicone fluid. The was some discussion of it expanding as temps rose, that would not be a good situation. A friend of mine has a 66 GTO and had a lot of problems with dragging drum brakes, he had the DOT 5 fluid in the car. He has since flushed the system repeatedly and now uses a DOT 4 fluid, no more dragging brakes.
 

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I've had Dot 5 in my '65 HiPo since 1998 when I converted it to factory manual discs/drums when I rebuilt the brake system as part of the restoration. The car now has a bit over 18K miles since being put back on the road in Mar 2000. Absolutely no issues to date.

I've heard comments that Dot 5 may result in a 'soft or spongy' pedal compared to Dot 3/4. So far that has not been an issue for me.

I do know that if your system currently has Dot 3 or 4, it must be completely flushed out with, I believe, denatured alcohol. If I'm wrong hopefully another VMF'r will set me straight.
 

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My 65 has had Dot 5 since 1992 and works perfectly. The pedal is firm.

Dot 5 beats the pants off Dot 3/4 for a car like mine. I never have to worry about damaging the paint.
 

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Hmm... a topic for debate!

Negatives of DOT 5/Silicon brake fluid:

1) subject to aeration, hence you should probably not shake up the can of fluid before adding it and don't use a pressure bleeder that uses air pressure...

2) slightly more compressible than conventional brake fluid - some claim it to give a spongy feel but I think this may be the effect of aeration.

3) totally incompatible with DOT3/4/5.1, so if someone adds even a little bit of the wrong stuff you will need to flush everything.

4) Will not absorb water. Hey, that good right? If water enters your system, it will sink to the low point. If that happens to be your caliper, then the boiling point of water is easily reached in normal operation. Not good!

5) Not compatible with some anti-lock brake systems.

6) Expensive.

I still use it.

-Rory
 

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There are few negatives for street-driven cars to switch to DOT-5 when done right. The spongy brake issue is often a result of small bubbles in the line--when silicone brake fluid gets aerated, it is very difficult to get the bubbles entirely out. This means be very careful when bleeding and adding fluid and you'll be fine. IIRC, silicone is also more sensitive to heat issues, so hard driving may require more conventional DOT-4 or specialized fluid. The benefits for a well done silicone swap are less hygroscopicity (no water attraction chemically, slight amount with the heat cycle) than conventional alcohol based brake fluids and no paint stripping qualities. JMO. Your results may vary. :D
Daniel
 

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Stop Tech has a good article on brake fluid tech. It's mostly geared towards racing, but good info.

I use AP Super 600 in my 66, the brakes are bled before every open track event (5-7 / year).

Good peace of mind ;)
 

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I am now using DOT5 in Midlife, and glad I did. The lines leaked like crazy, and would have lifted up all of that gorgeous paint everywhere had it been DOT3. That said, DOT5 does seem to leak a bit more than 3, and my pedal is not as firm as I remember it should be. The advantage of no paint removal far outweighs any disadvantages cited above.
 

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Only two negs that I know--

Must flush out DOT3/4 with denatured alcohol, then completely blow out the alcohol, before installing.

If water does get into the system it sinks to the low spot and corrodes whatever it touches.

If I ever do a complete system renew, I will prolly use DOT5
 

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Now I wanted to use this in my 67 for the paint reasons alone.. COuple questions though. My lines are new, as are my front calipers.

my M/C and prop. valve, as well as rear (SN95) calipers, all came from the wreckers.. Is it possible to flush these out substantially? I'd hate to have to use Dot3/4 just because of this (Or replace all those components, but that seems unnecessary). I was thinking of just bench bleedig the m/c with alcohol, but not sure about the rest..
 
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