Dick B was spot on the money about his thoughts on Dot 5, which is not unusual for him to be correct. I have done the same conversion to Dot 5, about 13 years ago. I would add to what he posted that I used some commercial brake cleaner ( Brakleen or whatever brand you prefer ) and used that to flush the system after replacing the various rubber components. I doubt that the cleaner he used would cause any problem, but since the various metals involved - particularly the cylinders - have a degree of porosity, I didnt want to have any doubts that any and all " contaminants" were removed from the system. There is also some new, non chlorinated brake parts cleaners available but imho after using them...they suck big time. But thats just my point of view, the main idea is to make sure theres nothing in that system but the brake fluid involved. Mikey 62 Crown Coupe p.s all the dot 4 , dot 3/4...its basically the same glycol alcohol based stuff, its hygroscopic as regular dot 3 and if youre gonna do this, go to dot 5 or dont bother.