Storage fluid for brake cylinder

[wwheeler]

I have a brake cylinder that is virtually new that I want to store for a few years. What fluid would be the best to flush it with for storage? Brake fluid will absorb water, Castor oil (DOT2) might gel over time. I want to make sure the fluid is compatible with the rubber brake parts.

Thank you.

Wallace

[Shvegel]

Silicone DOT5 but look into compatibility issues.  Can you use DOT5 and flush it out and refill with DOT4?  Seems like if you just refilled it with Clean DOT4 and sealed the openings you would be fine.  I have seen more than 1 brake proportioning valve(just forward of rear axle) not live through storage.  I would flush the entire rear brake system with clean DOT4 and then plug the openings when you pull it.

One more thing if you do use DOT5 keep it away from the paint as it is Silicone based and will drive a bodyman nuts.

[Mike K]

Ive just replaced the master brake cylinder after renewing the whole braking system.
The old MBC seemed to still be working fine, in any event I replaced it for good measure. Same as Shvegel's input above, flushed and filled it with clean DOT4,  plugged and stored it away.

[wwheeler]

I am still not totally happy with keeping the water absorbing fluid (DOT 3 or 4) in the brake part even though it is sealed up. DOT 5 has to be totally flushed out and is not compatible with DOT 3 or 4. I called a well known brake rebuilder and they suggested  the following:

1) Disassemble the entire unit and cover with oil soaked rags. Not an option for me.

2) Store with brake assembly fluid. Something like Raybestos BAF12. According to what I have read, it is compatible and won't absorb water. This is probably what is inside the new brake cylinders when you get them. I never knew this stuff existed and not expensive.