[TR] [EXTERNAL] Re: Brake fluids again

[Don Hiscock]

Randall (and others), any experience with a solvent flush prior to bleeding
in the DOT5?  ISTR an isopropyl alcohol flush can do a better job of
evacuating residual DOT3 than a wet switch.  Makes sense, but I have no
hard data.

I'm in the process of planning for DOT3 to DOT5 conversion on my car, and
I'm leaning toward leaving the existing rubber seals in place.  If there
are ways to do this that are better than others, it would be good to know.

Don

On Thu, Apr 16, 2020 at 12:36 PM Randall <TR3driver at ca.rr.com> wrote:

> This is a debate that has been going on for literally decades.  To be quite
> honest, my own opinion has changed somewhat over those decades.
>
> You certainly can convert by just draining, refilling with DOT 5, and
> bleeding each corner until you get clean purple fluid.  Although the two
> fluids will not mix (kind of like oil and water), they are fully compatible
> and can co-exist peacefully in the same system.  And the result, IMO, will
> certainly be better than not converting at all.  I've done it myself
> several
> times and always been happy with the result, at least at first.
>
> But, there are two drawbacks that I see to this approach.  One is that
> there
> are little pockets of DOT 3 or 4 that remain in the system and continue to
> do what DOT 3/4 does, ie absorb water, deteriorate, and become corrosive.
> It also retains it's lower boiling point (which continues to go down with
> time).  If you read through the Holbrook paper, they had a test failure (a
> 73 MB 200) that lost it's brakes during the test, and they attributed that
> failure to having only 4% of conventional brake fluid still in the system.
> They retested the same car after "properly" converting to DOT 5 (which
> presumably means removing that last 4%) and got better results.
>
> The other is that sometimes, not often and certainly not always, I have
> seen
> sudden failures with "rubber" components that were used for a long time
> with
> DOT 3/4 and are now exposed to DOT 5.  You can certainly argue that they
> were old and about to fail anyway; but old seals generally just get hard
> and
> don't seal as well (slow leaks).  They don't turn soft and tear, suddenly
> rendering them useless.
>
> Just for an example of what I'm talking about, I converted Stag #1 to DOT 5
> shortly after buying it, by just bleeding through.  Worked great at first,
> but months later the brake pedal started sometimes slowly sinking to the
> floor at a stop light.  At that time, I didn't want to rebuild the MC
> myself, so I made an appointment with a shop in Pomona that was supposedly
> familiar with Stags.  On the way to Pomona, within just a few miles of each
> other, both cups in the MC failed in the same exact fashion.  They turned
> as
> soft as Gummi Bears, and tore through the base of the seal.  This is not
> normal seal wear!
>
> So, my current opinion is that, if the choice is just to "bleed through" or
> not convert, it's certainly better to bleed through.  But what John Deere
> (my former employer) calls "best practice" is to clean the hard lines and
> replace all the seals and hoses with new.  The result is more likely to
> give
> you decades of service with no further problems.
>
> As a side note, DOT 5 also gives a very slightly softer pedal than DOT 3/4
> does.  You can compensate for this effect by converting the soft lines to
> the "braided SS" lines, which use a much harder tube inside and hence don't
> swell as much under pressure.  I got the ones for my TR3 at Tsi in Ohio;
> the
> Stag lines came from Rimmers.  ISTR Ted later told me that they can make
> them up for Stags as well.
>
> -- Randall
>
> >  Can I
> > drain out the existing DOT 4 and switch to DOT 5?
> >
> > Or do I need to completely flush the entire system and
> > replace all the wheel cylinder, master cylinder, and clutch
> > master and slave cylinder seals when converting from DOT 4 to DOT 5?
> >
>
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