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 Posted: 01-10-2022 03:29 pm
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rederic48
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Hello
I am intending to overhaul the brake system on my 73 JH and intend to change to silicone brake fluid. Anybody know what quantity I need to buy to fill the system? Bought new master and rear brake cylinders plus seals for front callipers. I intend to blow through the existing brake pipes with compressed air.
Thanks

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 Posted: 01-11-2022 11:14 am
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subwoofer
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Any particular reason you want to go through the trouble of changing to silicone fluid? If you cook your brakes on a regular basis, DOT 5.1 fluid has a higher boiling point than DOT 4 but no special procedures required. If you for some reason manage to introduce droplets of water into your silicone filled system, getting them out again may be a challenge as the fluid and water won't mix, while with regular brake fluid you just need to flush out the old.

Silicone fluid is supposedly more compressible too, so is said to give a softer pedal.

--
Joachim

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 Posted: 01-11-2022 02:21 pm
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gmgiltd
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DOT 3,4 and 5.1 are glycol based and DOT 5 is Silicone based - glycol and silicone based fluids are not compatible with each other. In my case I upgraded the brakes to larger vented discs with 4 piston radial calipers on the front and rear discs with 2 piston calipers, but retained the original master cylinder. The braking system was previously filled with DOT 4 . The manufacturer of the discs and calipers (Hispec) advised me not to under any circumstances mix the two as the seals would be damaged -competition brake systems and road car upgrades are their core business so I would suggest that they have some experience in this field. DOT 5.1 has an even higher boiling point than DOT 5. Dot 5 silicone is more suitable for competition cars where the fluid is changed regularly - on a road car moisture will not be diluted in the fluid so if the brakes are worked hard the water can rapidly go from non compressable fluid to compressable steam vapour resulting in no brakes.
Gordon

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