Master Cylinder Mod For Disc Brakes Conversion

[Willie]

Yes nine years is excellent except that the manual
recommends that all rubbers are changed after three
years,fluid changed,etc. I have ordered three new
flexi hoses as I have learned my lesson BUT I must state
that I have NEVER drained and replaced the brake fluid
on ANY if the 47 cars which I have owned over the years!
Except as a result of fitting a new master cylinder(on two
of them)and have never had trouble with 'vapourised'
fluid. '57'....the rears are operating and releasing very
well!

[Chris Morley]

An interesting observation from Willie and I've never yet read a good explanation for why brake fluid must be replaced at frequent intervals. Surely there's no reason to do it unless the brake fluid's characteristics change over time? Or is this requirement quoted just in case water gets in the brake circuit?

[57traveller]

Must pay more attention to the manual!

The only reason I've seen is that brake fluid attracts moisture from the atmosphere, (hygroscopic - is that the right word?). Over time an accumulation at the wheel cylinders will, to use Willie's word "vapourise," because of the heat generated when braking, therefore loss of brake efficiency.

[Kevin]

Yes 57 that is the correct term for a substance that obsorbs water, I am not quite sure how it occurs but we have all had cylinders at some time where rust has occurred, maybe it can be drawn in through the master cycilnder over time.
As for vapourising this can occur when the brakes overheat and the brake fluid boils which of course leaves air in the system, I assume this is caused by water/moisture in the system making things worse but I am not 100% sure, but I do like to change the fluid occasionally (every few years) because as the system is not totally sealed it will eventually obsorb moisture unlike silicon fluid which is not hygroscopic.

[Willie]

I have seen articles which state that the brake fluid is so
hydroscopic that it can absorb water THROUGH the rubber
Flexi brake hoses!! If that is so then why doesn't fluid
ooze OUT of the flexi hoses???

[Kevin]

Maybe it happends when they swell slightly which is why cars that use Aeroquip or other braided hoses have a firmer pedal due to less flex, we obviously need an expert in atmospherics or some other mystical science.
On a different tact a similar thing happens with plaster if it becomes damp because of an iffy damp course, when the dampcourse is repaired/renewed the affected area has to have the plaster removed and replaced as once it has been damp it generates/retains hydroscopic salts which then attracts the moisture from the room atmosphere making the internal surface feel colder/damper than normal.