Posted by Clint Dixon [172.70.126.157] on Monday, September 26, 2022 at 20:20:32 :
In Reply to: what DoT brake fluid posted by Galen [172.70.135.202] on Monday, September 26, 2022 at 07:25:45 :
I recently replaced all brake components on both my '47 WDX and my '51 B3PW. I seriously thought about going with DOT 5 but first I did a lot of research.
We all know that DOT 5 is silicone based and does not absorb moisture and/or spread it throughout the entire contents of the brake fluid in the system. This where my research started getting interesting.
Brake systems will naturally draw moisture into the lines, hoses, and cylinders because of the heating and cooling of the environment and the components making up the brake system. Add to this the up and down atmospheric moisture conditions that change with the seasons.
As we know, this moisture gets absorbed by, and spread throughout, all of the conventional DOT 3 brake fluid that is in the system. Whereas, DOT 5 does not absorb and spread it throughout, the lines, hoses, and cylinders still attract moisture. This moisture pools when in DOT 5. Where does it pool? The low spots - the cylinders, where rust and pitting then start.
So it has been advised that when using DOT 5 brake fluid in collector vehicles that do not get driven regularly, to drain and replace the DOT 5 each year. Yeah, DOT 3 still collects moisture but it is held in suspension to some extent until there is enough saturation of the fluid that the moisture then pools.
Short answer, DOT 5 needs to be drained and replaced more frequently than DOT 3.
I ended up going with DOT 4 which is supposed to be resistant to higher temperatures and MAY not absorb moisture as quickly as DOT 3.
In any case, I am tired of replacing wheel cylinders every few years. My solution, that has worked well so far, is to bleed the brakes once a year to not completely replace the fluid that is there, but to "refreshen" it.
Junior
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