[TR] 59 tr3 brake fluid flush and fill.

Randall TR3driver at ca.rr.com
Sat Oct 27 05:54:10 MDT 2018

> I want to replace dot 3 with dot 5?  I need to replace 
> leaking clutch m/c and was wondering correct procedure to 
> flush and fill with dot 5 before I do brake line and clutch 
> m/c or just replace parts and then replace brake fluid? 

We have discussed (and re-cussed) that topic many times.  There are several
different camps:

The most extreme is to replace all the seals and lines, cleaning the
cylinders with solvent (as part of replacing the seals).  Rear cylinders may
need to be replaced (inspect the bores for pits); likewise pistons in front
calipers.  Use the "braided SS" soft lines (which are really Teflon inside,
the braid is to protect the Teflon).  

To be honest, I think there is something to be said for this approach;
particularly if any of those components are original.  They don't last
forever, original components are coming up on 60 years old and are bound to
be near the end of their useful lifetime.  If not changed on a regular
basis, DOT 3 becomes corrosive and can weaken even the hard lines.  I have
had one of the soft lines from reservoir to MC snap in my hands (although it
wasn't on my car at the time).

At the other extreme, just fill with DOT 5 (after making any necessary
repairs) and bleed at each bleed screw until no more DOT 3 comes out.  I've
used this approach as well, and it has worked out for me.  IMO it's not as
good as changing everything as above; but still better than continuing to
use DOT 3/4.  There are two downsides: 1) You are still running around with
components that may have been damaged by DOT 3/4 (and are near the end of
their useful life), meaning you will have more failures in the future.

And 2) there will be some DOT 3/4 remaining in the system.  It doesn't all
come out.  It will remain separate from the DOT 5 (they don't mix, kind of
like oil and water) and will continue to deteriorate, eventually turning to
a black goo.  Doesn't seem to be particularly harmful, though.  One oddity,
the leftover DOT 3 will actually suck the purple dye out of the DOT 5!

There is a thoughtful article at
That covers all this in far more detail.  

FWIW, that article references two papers presented to the SAE, which can be
found at

One last point, if you do replace the hard lines, I like the "Cunifer" sets
made by Automec and sold by Moss.  Cunifer is a special copper/nickel/iron
alloy developed specifically for brake use, and championed by Volvo as being
safer than conventional steel line (especially in areas where they use salt
on the roads).  It has the added benefit of being much easier to shape and
bend than steel.

-- Randall 
56 TR3 TS13571L once and future daily driver
71 Stag LE1473 - awaiting engine rebuild
71-2-3 Stag - awaiting gearbox rebuild 

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