Rear brake cylinder question

5 must be the silicone stuff

Yes, Dot 5 is the silicone stuff. I use it exclusively in my Classic/Vintage car collection as Dot 5 is Hydrophobic. Since the old cars don't get much of a run the silicone-based brake fluid protects the steel parts from rusting and if you spill some it doesn't stuff up paint. Most of my pre- and immediately -post war cars are painted with Vitreous enamel and they need to be protected. If using Dot 5, all previous brake fluid must be removed as they are incompatible, silicone and polyethylene glycol. Also, gotta make sure no air enters with silicone as it is absorbed and will lead to failure or at the very least, sponginess.

dot 5 silicone fluid isnt Hydrophobic normal dot 3 4 5.1 is plus silicone has a lot lot more higher boiling point well thats what i was lead to belive

Doesn't a hydrophobic fluid cause problems if there are any water drops in the system, with no way to absorb them they can just lie around and corrode?

facade wrote: Doesn't a hydrophobic fluid cause problems if there are any water drops in the system, with no way to absorb them they can just lie around and corrode?

hydrophobic means adsorbs water silicone repels water i think

I thought hydroscopic meant it absorbed water?