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silicon brake fluid
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ukdave2002



Joined: 23 Nov 2007
Posts: 4100
Location: South Cheshire

PostPosted: Thu Jul 09, 2020 2:20 pm    Post subject: Reply with quote

I think that technically all glycol brake fluids must be synthetic? the brake fluids that you shouldn't mix are silicon and mineral.

Dave
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Ray White



Joined: 02 Dec 2014
Posts: 6286
Location: Derby

PostPosted: Thu Jul 09, 2020 2:27 pm    Post subject: Reply with quote

ukdave2002 wrote:
I think that technically all glycol brake fluids must be synthetic? the brake fluids that you shouldn't mix are silicon and mineral.

Dave


Yes but my point is that DOT 4 always was mineral but the DOT 4 on the shelf in the shop says SYNTHetic.

What happens if I add the DOT 4 synthetic to the DOT4 in my car which I remember to be mineral?

I thought synthetic was DOT 5 so always knew what to avoid. Now I don't know what to do.
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ukdave2002



Joined: 23 Nov 2007
Posts: 4100
Location: South Cheshire

PostPosted: Thu Jul 09, 2020 2:42 pm    Post subject: Reply with quote

Ray

Mineral fluids are all synthetic, there has never been a "natural" brake fluid, the word synthetic is probably added to the can by marketing folk!

synthetic does not equate to silicon Smile

Dave
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Ray White



Joined: 02 Dec 2014
Posts: 6286
Location: Derby

PostPosted: Thu Jul 09, 2020 2:50 pm    Post subject: Reply with quote

ukdave2002 wrote:
Ray

Mineral fluids are all synthetic, there has never been a "natural" brake fluid, the word synthetic is probably added to the can by marketing folk!

synthetic does not equate to silicon Smile

Dave


It's just me getting discombobulated again!!!

I have obviously been labouring under the impression that synthetic = silicon.

Thanks for putting me right.
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Miken



Joined: 24 Dec 2012
Posts: 544

PostPosted: Sun Jul 12, 2020 8:57 am    Post subject: Reply with quote

In my experience ,if you want to know about oils and lubricants, the best people to ask are the people who make the stuff.
Choose a manufacturer and ring up their technical department. They are always very pleasant ,knowledgeable people who are always seem happy to answer your questions. A couple of Weeks ago I wanted to know which oil to run in my Devon pick up so I called Morris oil, Penright, Castrol and Miller oils. All very helpful.
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lowdrag



Joined: 10 Apr 2009
Posts: 1585
Location: Le Mans

PostPosted: Sun Jul 12, 2020 4:58 pm    Post subject: Reply with quote

I have never had a problem with glycol-based fluid - no bubbles, no water, no rust, and the only difference between DOT4 and 5.1 is the boiling point. For spirited driving use the latter. I have used 5.1 for years, and always keep a couple of sealed litres on the shelf.
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Richard H



Joined: 03 Apr 2009
Posts: 2148
Location: Lincolnshire, UK

PostPosted: Wed Aug 04, 2021 7:54 pm    Post subject: Reply with quote

In addition to the drawbacks of silicone fluid mentioned above, it is also thinner, so in certain cylinders where the seal tolerances aren’t great anyway, you can get leaks.
Examples of vehicles to avoid silicone fluid with:
Anything Italian, using ‘donut’ seals in their braking systems.
Anything with o-rings in the braking system (not the best seal in the world!) French Record master cylinders commonly do, but apart from those they’re rare.
Anything with a remote servo, especially some of the older models. One major servo reconditioning company goes so far as to say you will void your warranty if you use silicone.

I would imagine on a car like Keith D’s Devon, which has decent cup seals in the wheel cylinders and seals with good tolerances in the master, you will have no problems at all.
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Richard Hughes
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