Originally Posted by wrinx
You are joking I hope....mad advice!
Still crazy after all these years!! Hahahahahahaha!
Anyway, DOT5... it's a silicone-based fluid that's less prone to absorbing moisture from the atmosphere, so it gives more consistent results in operation.
The trade-off is that it is not "oily" like DOT 3 or 4.
Some brake systems (master cylinders) have seals that require lubrication.. adding DOT5 to these is like running unleaded when you have soft valve seats - the seals lose their lubrication and so eventually tear.. leading to leaks.
DOT5 is largely insert, so should mix okay with other fluids but if you're going to use it, best to drain out the old stuff first. There's no need to dismantle your brakes, just top it up with DOT5 and pump the brakes until the new flkuid comes out.. most of the old stuff will be gone then.
I'd be more wary of mixing DOT3 and 4. I just don't know what the difference is there but I presume it's reasonably significant.
Newer brake systems should be able to deal with DOT5 as the seals and o-rings they use are more durable than the older ones that need lubing. DOT5.1 is more oily though, I think so maybe a better bet for extended use.