by 1972nail » Thu Aug 20, 2015 11:54 pm
My understanding is, and I my be wrong, that it's not the fluid that is corrosive but the water that it absorbs. I was tempted to use Dot 5 or 5.1 silicone but as many of my parts were nos and built up in the factory with Dot 3 or 4 as a lubricant I went for Dot 4. Dot 4 and Dot 5/5.1 don't mix.
Changed every couple of years Dot 4 is OK. When it absorbs moisture from the atsmosphere it becomes corrosive and 'boils' at lower temperatures causing brake fade in high performance applications. Dot 5 and 5.1 don't absorb moisture.
I don't keep opened bottles of Dot 4 for long as it will absorb moisture and age just as quickly as the fluid in the braking system. I replace the Dot 4 every couple of years in my cars with fluid from fresh unopened bottles and have had no problems with corroded cylinders, even in our Minor which doesn't have effective seals to keep moisture out of the cylinders.
Editor of the VVOC Magazine ReVival
"When you have a Firenza like mine, who needs any Minis?" copyright David Maxwell 1979.