yes i made additional posts
http://www.7173mustangs.com/thread-the-gift-that-keeps-on-giving-part-3
http://www.7173mustangs.com/thread-master-cylinder-experiment
Here is what i found: soaking the parts in dot 3 for a while then reinstalling the parts and using dot 5 Did have a positive effect things did stop leaking. i could not find a measurable difference in the parts with the measuring equipment i have however my weeping leaks stopped.
what i found was when a new system used dot 5 directly the rubber parts did not swell as they would have with dot 3, that left extra tolerance in the new seals and you ended up with small weeping leaks of brake fluid.
this makes sense as dot 2-3-4,5.1 is known to swell rubber as has additives to reduce swelling. dot 5 originally had a major problem it did not have enough swell additive in it and there was a big recall on the first batch some years ago. however there is still something missing from dot 5 as car manufacturers scrambled in 2006 with factory recalls to change rubber orings in master cylinders my Acura had a recall like this because of Dot 5.
now the best is stick with Dot, 3,4,5.1 if you have a brake system in good shape.
if you plan to race the car then go to dot 5.
dot 5 has a higher boiling point but lets water pool up in the system causing point areas of corrosion.
dot 3,4,5.1 all absorb water, and then overall the system gets moisture inside.
Dot 5 has the advantage of not eating paint. so its a real toss up. dot 5 gives you a different pedal feel as well.
was switching over to dot 5 a good thing for you? well maybe / maybe not
if the fluid is switched out like every 5 years then you have no problem with moisture. most classics do sit around but the fluid is usually newer then a daily driver so corrosion from water is much less a concern. was he right to change you,,, again could be a yes or no situation. dot 5 can cause major problems in some cars.
yes the dot 5 fluid could be better in fighting moisture in the brake system, but a system in good shape won't have much moisture in it anyway.
i used to be a big dot 5 guy now i wouldn't have been i would of gone with dot 4 or 5.1 instead with the knowledge i have now.
if a system is rusty inside then you want to change the brake lines anyway switching from dot 3 to 5 does nothing for you.
if you flush the dot 3,4,5.1 out every couple of years then they will pretty much last forever, that gets the moisture out.
the preferred method of switching from dot 3 to dot 5 is to flush the system with 100% alcohol, getting all the dot 3 out that you can.
however this can damage the rubber seals. you can flush out the dot 3 with dot 5 you just have to use A LOT of dot 5 keep flushing the lines until the purple dot 5 is nice and clear of contamination from dot 3 and then bleed the entire thing flushed through again just to be sure.
you can change back to dot 3 again you need to flush the system a couple of times and use lots of fluid to push all the silicone out.
the mix between dot 3 and dot 5 produces a kind of varnish gel over time and that can clog up the prop valve or a restriction may build up inside one of the hoses. it can make caliper pistons stick in the bore.
i think when you switch over from either there should be a major flush then 6 months or a year later in the spring when you get ready to drive again flush the entire system one more time to make sure. the fresh fluid is a good thing anyway.
now it comes down to do you currently have a leaking dot 5 system, if you do then i would think about switching back to dot 3 or 4 or 5.1
if you do not like the pedal feel of dot 5 then also think about switching back.
if you don't have any issues then i say leave it alone and keep an eye on it during maintenance for a couple years.
right now spring is coming so i will be testing my experiment for year 2 to see how things are holding up if i start to see weeping leaks again i will be switching the dot 5 out finally and putting in most likely Dot 4 brake fluid.
one thing to make sure is did the mechanic switch you from dot 3 to dot 5.1 that is a different story as that is compatible it is glycol based.
some times people hear dot 5 but they don't know there is dot 5.1 and those are very different.