That is interesting, Randall, and as Rick says, the compressability effect
is too small to notice - I didn't notice it (in fact because my swap
involved a full bleed through, my brake pedal got stiffer, not softer). I
can lock up all four wheels on my TR4...
There are some reports, apparently in error, of DOT 5 having a lower boiling
point. From the VTR maintenance section:
- "DOT5 is slightly compressible (giving a very slightly soft pedal), and
has a lower boiling point than DOT4. "
One complaint I heard against DOT 5 is its expense. Yes, the bottle price is
more (double?) but any economy quickly disappears when your DOT 4-filled
master cylinder fails and you find a large area of ruined paint under the
hood, as I found, nevermind that also as DOT 5 doesn't absorb water, it need
not be routinely replaced like DOT 3/4 *should* be, every 3 or so years.
Brian
On Thu, Nov 12, 2009 at 12:54 PM, Randall <tr3driver@ca.rr.com> wrote:
> Little early in the season for fluif wars, isn't it?
> <G>
>
> > I thought the non-issue about DOT 5 was about it having a
> > slightly lower boiling point than DOT 3 or 4, rather than a
> > reduced hydraulic capability.
>
> Actually, the DOT 5 specification calls for a higher minimum boiling point
> than either DOT 3 or 4.
> Dry 3/4/5 = 205C/230C/260C
> 'Wet' 3/4/5 = 140C/155C/180C
>
> But in use, the DOT 5 stays relatively dry; while DOT 3/4 will absorb
> moisture and salt right through the brake lines, to give a boiling point
> even lower than the 'wet' specification.
>
> http://s258.photobucket.com/albums/hh260/TR3driver/Brake%20Fluid/?action=vie
> w¤t=Browing2Table3.jpg
>
> However DOT 5 is slightly more compressible, which does result in a
> slightly
> softer pedal. Worse, from a racer's point of view, it becomes more
> compressible as it gets hot, so the pedal gets progressively softer during
> a
> race.
>
> -- Randall
>
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