Brake fluid experts out there?
 

In my formula ford I have girling master cylinders. I have been using dot 3 synthetic. They have worn out with very little use. Dot 4 is recommended. Is it possible the dot 3 synthetic ate away the seals in the girling mc's?
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AFAIK DOT3 and DOT4 are totally compatible, and would provide similar results. Quie odd.

-J

DOT 4 has a higher boiling point but also appears to have a higher borate concentration to get that boiling point.

The rubber compounds in the brake system need to be designed to accept this higher borate concentration without excessive deterioration.

Many folks interchange DOT3 with DOT4, but unless absolutely necessary for a high performance vehicle, I'm not convinced it's a good idea.

Which Dot3 synthetic?

Prestone (or is it penzoil?)

You'd go with the dot 4?

I must admit that I've used the DOT4, believing that it is a "better" brake fluid.

However, as mentioned, I'm not convinced that the higher boiling point is worth the tradeoff of increased borates which can degrade the rubber in the system at an advanced rate (unless the system was specifically designed for DOT4).

Both of those should be Glycol, not Silicone based, so you're good there.

The guy I bought them from ( a formula ford guru) said to use DOT4. I'd always prefer to use synthetic if possible and if it does not attack the European seals. Course a lot of his customers are road racers who have to use their brakes a lot more and with more duration than we do in autocross.

Of course he did.

But, if you queried him as to the technical benefits and potential problems associated with DOT-4, you'll probably find, like most mechanics, their recommendation is anecdotal and without any support.

Just because it has a higher boiling point doesn't necessarily make it "better" for a street vehicle. None of us ever push a street vehicle to the level where the boiling point matters.

If the boiling point is truly of concern, you and all others should be changing your brake fluid every two years, as a minimum. How many of us actually do that.............and how many have suffered boiling of fluid due to the failure to do it?

Its not for a street vehicle its for my formula ford. I have no concern about boiling it I just want the seals to hold up.

Why do you have no concern about boiling on a racing vehicle?

Isn't it subjected to extreme braking under long duty cycles?

The only reason for DOT-4 fluid is to raise the boiling point. They did invent it for a reason................

I believe I have seen some fluid that was DOT3 and DOT4. Can I assume it is DOT4 and therefore encompasses DOT3?

Autocross runs are usually about a minute long. Tough to boil brake fluid in 60 seconds.

I bet a convection burner could boil Dot 4 brake fluid in 60 seconds.