Now this is weird. I posted a while back about my brake fluid, thinking I had silicone because it was odorless and didn't eat away at my paint. I was under the impression that all DOT5 silicone brake fluid was compatible so I bought some more from NAPA and used it to refill my MC as I was bleeding. I wanted to check how the two fluids mixed (the old that I thought was DOT5 and the new actual DOT5), so I poured the excess through a coffee filter into a clear plastic bottle. Most of the fluid went through, but then there was a clear fluid that didn't permeate the filter and when I dumped into the bottle, it stayed on top of the old fluid. So, my question is, how screwed am I?

 

Achh, I figured it out. The brakes were bled by a shop I brought it to to have the exhaust system put on. They probably put DOT3 or 4 in the MC and I didn't remember to tell them I had DOT5 in it. So, now I have to take up the task of flushing the entire system with alcohol. I have access to 90 proof and 200 proof at work. Which one should I use that won't eat the rubber hoses?

 

I have always used plain old isopropyl that I purchased from the local drug store. Usually a couple of bottles (less than a buck a piece) do the trick (just don't drink the left over!! ).

In your case since it's unlikely that the Dot 3 has made it to the calipers, I personally would just disconnect the lines from the calipers and flush the lines only. Flushing through the calipers (bleeders) will undoubtedly get some of the Dot 3 into the calipers. While it is true the two don't mix, the only harm in having both in the system is that you still have the potential for corrosion due to the Dot 3's hygroscopic properties. Contrary to some opinions, they will not gum up a perfectly good system if they get mixed... To avoid any mixing is why I would just flush the lines however.

I'm guessing that when you disconnect the lines, you will see silicone fluid well before you see the Dot 3. You can then introduce the new silicone until it pushes all of the alcohol out, before reconnecting it to the caliper, or disconnect the lines at the master cylinder and let the alcohol drain through then blow the lines out before adding silicone. I have used both of these methods to flush the master cylinder and the lines many times with no problems.

Then just bleed you brakes normally taking extra care not to aerate the silicone fluid by pumping the brakes vigorously. There are a myriad of techniques for bleeding and a search here will reveal enough to confuse a genius. I always ask the wife for help, so she realizes owning these machines is work and of course I couldn't do it without her…
Good luck… GUSTO

 

The issue with DOT-3 should not be a problem for you if it has not been in the system for a long time. The problem comes from an older system that has had DOT-3 in it long enough to absorb some moisture. The DOT-3 can absorb moisture over time and some of this moisture laden fluid will soak into the rubber parts in the system. If you convert to DOT-5 without replacing the old rubber parts, the old DOT-3 can leach out and cause problems associated with wet DOT-3 even though you have converted to synthetic.

Stainless Steel Brakes Corp reccomends (and prefers) using fresh DOT-3 as a line flushing media over using denatured alcohol when doing the DOT-3 to DOT-5 conversion. If you do not get all the alcohol out of the system, it can vaporize easily at a much lower temperature and cause a spongy pedal. This assumes you have already replaced all the rubber hoses, caliper seals, and master cylinder and are just using the DOT-3 to flush the hard lines.

SSBC sells a darn good book on the Vette Brake subject and it is well worth having a copy in your library.

-Mark.

 

If you use compressed air to blow out the lines, be sure it is de-humifified... i.e.- use at least -two- air/water separators (I use 4). Otherwise, you're just coating the inside of the brake lines with water mist. This is bad regardless of which type of fluid you use.