11-30-2017, 08:45 PM
I understood that the reason you should change brake/clutch fluid regularly is because it is glycol based (DOT 3 & DOT 4) and therefore hygroscopic ie it absorbs airborne moisture.
Water in the fluid may well change its colour, but more to the point it attacks the slave and master pistons in the system which are usually only chrome plated steel - hence the fuss about upgrading to stainless steel (corrosion free) brake caliper pistons on many classic bike forums. Indeed the water is heavier than the fluid, will eventually work is way down to the lowest point (brake caliper or clutch slave cylinder), corrode the piston that then rip the seals.
Whilst rebuilding a couple of my classics I changed to silicone fluid (DOT 5) that is not hygroscopic and will theoretically last forever (found in Harleys). However, you cannot drain out a system that has once used DOT 4 and then refill it with DOT 5 - they are not compatible.
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Water in the fluid may well change its colour, but more to the point it attacks the slave and master pistons in the system which are usually only chrome plated steel - hence the fuss about upgrading to stainless steel (corrosion free) brake caliper pistons on many classic bike forums. Indeed the water is heavier than the fluid, will eventually work is way down to the lowest point (brake caliper or clutch slave cylinder), corrode the piston that then rip the seals.
Whilst rebuilding a couple of my classics I changed to silicone fluid (DOT 5) that is not hygroscopic and will theoretically last forever (found in Harleys). However, you cannot drain out a system that has once used DOT 4 and then refill it with DOT 5 - they are not compatible.
Sent from my GT-N7100 using Tapatalk