Great, I was heard 🙂
It is about the chemicals it is made of.
The rubber material of the stock brakes can’t stand the “new” DOT5.
DOT4 is very similar to DOT3, both can be used and they can even be mixed. DOT3 is not available in Germany since many years. DOT3-brakes can be used with DOT4-fluid without any issue. DOT5 is something different.
You may compare it to the added amount of Ethanol in the fuel.
Up to 5 or 6% is ok, 10% is to much.
All rubbers in the fuel system will die when that will be used.
Difference of DOT3/4 and DOT5 is even more than that.
Might be like comparing fuel or oil or even water just as an example.
All of them are liquids but have complete different chemical “background[?]” !
That’s the reason why the letters on the covers say: “Use DOT4 only!”
On the other hand the latest bike and car models should have a cover that states “Use DOT5 only!”
Cheers, Michael
