DOT 3 and 4 fluids are compatible, they just have different boiling points. No need to drain & flush with alcohol or anything like that. Just siphon the reservoir, fill with fresh DOT 4, and pressure bleed (if possible) all 4 wheels. That's it.
DOT 5 (silicone) fluid is the nasty stuff that can cause problems... it's not hygroscopic (doesn't absorb water) and you can end up with rust or other problems due to that. Regular fluid absorbs water, which is good - but it's also why the fluid must be replaced every year or two! Some exotic race fluids have been reported to damage seals or other rubber bits, btw... but "normal" DOT 3/4 should never do that. :) -dm > ------------------------------ > Date: Wed, 25 Jan 2006 17:43:31 -0700 > From: "Bob Rentfro" <[EMAIL PROTECTED]> > Subject: Re: [MBZ] Tropming on the Brakes > > > The fluid is DOT-3, almost exactly one year old. Perhaps I'll switch it out > on next days off with DOT-4. Do I have to be super diligent and get all > traces of DOT-3 out before DOT-4 goes in? > > Bob Rentfro > '77 300D 148K
