Just wondering if all brake fluids are hydroscopic, that is they will absorb water. It seems that after 20 years or so my wheel/master cylinders are all rusty from non use. My 48 F3 is parked in a non heated garage and doesn't get driven a lot. Is the newer synthetic brake fluid better than traditional? What does the dot 3,4,5 mean?

Thanks,
Jameszee

 

I don't know if its the best but I use Type 4 and change it out every 3 years and I use speed bleeders on the wheel cylinders
Ed
near Philadelphia

 

DOT-4 has better wet/dry boiling points, but actually absorbs moisture faster than -3 and should be changed more often. Silicone fluids are the only ones that don't absorb moisture, but that doesn't mean moisture isn't in the system. Personal opinion, use DOT-3 and flush the system every 2 yrs. (applies to stock systems)

 

I’ve used silicone based DOT5 in my 56 F100 since 1982 and never had a problem with it. Got tired of replacing/rebuilding wheel cylinders and master cylinders because they would collect moisture from using DOT3 and rust. I’m in Florida and high humidity doesn’t help.