Joined: Aug 2017 Posts: 381 Threads: 16
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Location: Port Elizabeth, Sunny South Africa
Car type: '26 Chummy, '28 Top Hat, '33 Type "65", single seaters
Agree with Chris - DOT 5 & DOT 5.1 are NOT the same thing.
DOT 5 is Silicone fluid
DOT 5.1 is Mineral fluid formulated for ABS systems - Totally incompatible with DOT 5
Our daily drivers are all on DOT 4 mineral brake fluid, the classics with hydraulic brakes are all on DOT 5 silicone fluid and the Austins are all cable brakes
We've run '50's & '60's Giulietta Alfa's on DOT 5 Silicone for 21 years now, never looked back, but the change from DOT 4 Mineral to DOT 5 Silicone requires a total strip & rebuild & a comprehensive flushing of the lines & cylinders. Cleanliness is next to Godliness when it comes to brakes, Mercedes Benz SA determined that 0.04% mineral oil (ie dirty hands) in brake fluid is enough to destroy all the washers in the system.
If anyone wants to change over, contact me via Private Message & I'll walk you through the process
Aye
Greig
Joined: Aug 2017 Posts: 3,389 Threads: 105
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Location: Darkest Bedfordshire
Then we're agreed on most things Greig (especially the point about contamination) but I still don't understand why you'd choose silicone fluid over ethylene glycol...
Joined: Aug 2017 Posts: 327 Threads: 1
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Location: Bristol
Like Greg I have used silicone brake fluid for over 20yrs in Austin Sevens it does not absorb water and does not seize brake cyls when over wintered. Our first race car we used DOT 4, at the end of the race season it was winter stored for about 4 months when we were preparing for next season we found most of the brake system was seized it was stripped flushed and seals replaced silicone brake grease applied to the cyls and refilled with DOT 5 Silicone brake fluid we have not had a seized cyl since nor have we had to replace any of the seals so I don't what your problem is with silicone fluid. I have also done quite a few hydraulic conversions and always I advised to use silicone fluid, and have not known of any problems.
Terry.
Joined: Oct 2017 Posts: 1,504 Threads: 54
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Having seen a DOT 4 system drained after a couple of years, as per maker's recommendation, I can't imagine why anyone uses it. What came out was filthy.
Joined: Aug 2017 Posts: 3,389 Threads: 105
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Location: Darkest Bedfordshire
I don't 'have a problem' with Silicone brake fluid Terry I'm merely curious to know what advantage others perceive in using it.
It is not without merit - I've already mentioned low temperature viscosity (of little practical value to most people); it has a high BP (but is not alone in that respect); it is low-maintenance and yes, may improve resistance to piston seizure if a vehicle is laid up (which factors may indeed interest 7 racers and occasional drivers). It also doesn't attack your paintwork and has a relatively high flash point. On the downside though it is a relatively poor lubricant and thus not the best pick for long-term durability; it is vulnerable to aeration leading to 'spongey' pedal feeling. And whereas glycol-based fluids absorb water, any which finds its way into a silicone system remains as isolated globules which may vaporise, cause corrosion spots, or freeze. That's why most of the motor industry sticks with glycol. It's very much 'horses for courses' and if the benefits outweigh the demerits in any specific application then I'm all for it. Not sure I'd give it a blanket recommendation for all cars though.
Joined: Aug 2017 Posts: 327 Threads: 1
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Location: Bristol
No I would not recommend it for everything its not suitable for high pressure ABS systems anyway but for cars that are stored or infrequently used it does have advantages especially if the master/wheel cylinders are ferrous metal therefore for what most of the classic prewar owners who have hydraulics do with there cars it would seem most suitable Terry.
