I recently had the rear diff rebuilt in my 39 P-8-I also put in all new wheel cylinders. The Master is mostly empty-however, what's the recommended brake fluid-? this car isn't driven that much-Hasn't in the last 5 years-as I am now bringing it back-
I'm sure there is some type (?) of brake fluid in the lines-but what's the suggestion here-? and actually I am also thinking of replacing the Master Cylinder.-Suggestions-? Thanks, Dennis
I believe it is not good practice to mix DOT5 with other types of brake fluid, so I would go with what is in there.
The question is what was in there. The most likely is DOT3 (conventional old fashioned) brake fluid unless you have a specific reason to believe otherwise.
DOT3 is a pretty effective paint remover so if you take some existing fluid and let it sit for a while on a painted surface you don't care about you might get an answer. Hmmm. Now that I think about it, DOT3 is a good paint remover for old fashioned automotive lacquer and enamel paints. I don't know if it has the same effect on modern paints so maybe that is not longer a good test.
Dot 3 and others are all alcohol based,
Dot 5 is silicone based, Dot 5.1 is NOT!
You cannot mix these, so, if noct possible to determine, You have to drain the system.
Dot 5 is purple, but the color does not stay so over the years and fades!
If to choos after cleaning:
Silicone DOT 5 doesn´t take water, alcohol does and deteriorates!
So, You have to change alcohol brake fluids every 1 or 2 Years.
Silicone is used because in stored trucks, tanks etc. doesn´t need to be serviced.
Alcohol fluid is easier to find.
If searching: Harleys usually use DOT5 , at least here in Europe.
White Post Restorations that used to be the cream of the crop in brake restoration ALWAYS said to stick with Dot3. You are in AZ. so the idea of taking on water in the lines is about nill. IMHO.
Just did a master cyl. replacement on a '36 which is similar. As others suggest, go with Dot 3 and flush the lines with a brake bleeder a number of times to clear the lines starting at the farthest cylinder, then work forward.