View single post by gmgiltd
 Posted: 01-11-2022 02:21 pm
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Joined: 07-10-2012
Location: Whitehills , United Kingdom
Posts: 167
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.