Technical brake fluid, rebuild kits, m/c woes anew?

All brake fluid sold has to meet certain minimum federal D.O.T. standards for boiling point. But this doesn't mean they can't exceed the standard, and they do. I don't buy no name brake fluid at the dollar store or grocery, a good quality brand name DOT 3 will easily meet the published DOT 4 standards. I like it because the viscosity lends itself to very quick, easy bleeding of the system and a hard pedal.

 

is there anything to condensation building up inside 'for example'
a corvette style iron master cylinder, thats under the floor, with an exhaust running close to it
is the scenario an idea place for condensate to manifest
verus 'for example'
a plastic fluid jar under the hood with a screw type lid rather than a pair of wire clips

 

Wouldn't think so. Earlier brake systems are open to the atmosphere at the cap, they will pick up small amounts of condensation over time.

 

With the mul***ude of stops and hot fluid I'd guess a measure of that moisture eventually "boils out" for lack of due egghead terms. Like running an engine to full temp so the residual water (byproduct of combustion and simple heat cycles) can evaporate. Just to review this was ALL NEW STUFF. Lines, cylinders, master and fluid. Bled out to perfect pedal. Once ignored for about 3+ weeks the fluid leaked out the back of the cylinder and upon dis***embly revealed NO REASON for it. 3rd one in under a year, maybe it's my latest haircut

 

I am hating brake work right now...

 

This might help.

 

Or ... not.

First thing, it's actually spelled "Hygroscopic". Hate to be picky, but if somebody is gonna throw fancy words around, they gotta use 'em correctly. And it begs the question.

Then they go on to say that "unfortunately" brake fluid absorbs moisture. Yes, DOT 5 is good stuff, but it might not be good stuff in a 70 or 80 year old brake system open to the atmosphere.

Glycol based brake fluid was obviously chosen for brake fluid in no small part because it does absorb moisture. That's what you want. It wasn't some kind of oversight by the engineers. People don't get that.

So what changed when DOT 5 rolled around?

Better sealed brake systems, that's one thing. Aircraft use hydraulic fluid, not too much different than ATF. But it's an absolutely completely sealed airtight system.. Just about any liquid will work as a brake fluid, but there are limitations. I'm pretty picky when it comes to certain things but I think DOT 5 is a bit too fancy by half, and just more h***le than it's worth. Don't make things more complicated than necessary.

 

One indirect issue that you can possibly check out (under a high powered microscope)
are the annular lips of the seal cups where they round over from outside to inside and look for
defects where the edge would meet the wall of the cylinder. Occasionally in the process of pouring / injecting the uncured rubber into the mold the mold can be too cold or the mixture can be inconsistent and you end up with tiny tears, bubbles, folds (like leaves stacked upon each other) that can cause eventual leaks. These can be of any source from air, water, fluids etc either under pressure or vacuum and do not always show up immediately in your rebuild. True, the rubber parts of today are
different than what we had all used in the past, but the primary reason for this inconsistency
is directly related to the mold release products that the US manufacturers were forced into
using; the result was that most rubber products left the USA. Foreign suppliers in the past have been using good mold release products, but occasionally they cut corners and we're all left with the end result of bad rubber products. Sorry to be the bearer of bad tidings......

 

So, honed the cylinder with a proper brake hone and fluid as the lube just like has been the standard for decades. Plenty of time, good crosshatch, not like full polish, just a standard finish. Re***embled and cycled the plunger/o-ring/cup/check valve ***embly probably 100+ times. Felt like we were jerkin off a bull for samples! Anyways, put some fluid in the cylinder and hung it rod side down (where the leak was) for a couple days. Dry as a popcorn fart. In next week's episode we'll see if the fluid was the smart stuff @31Vicky with a hemi tried to warn us about or if we won. Film @ uh, hopefully never? But if it's fixed I will report back.