Just to be clear, DOT 5 (silicone) brake fluid does NOT (necessarily) have
a lower boiling point than DOT 3 or 4.
The DOT standards only set _minimum_ boiling points, wet and dry. They
call for 10% higher minimum boiling points for 5 over 4, and another 10%
for 4 over 3.
Although there are some racing fluids with higher dry boiling points, AFAIK
none of them has a higher wet boiling point than the DOT 5 minimum dry
boiling point for silicone. And, unless you change your brake fluid every
month (like the serious racers do), glycol fluid in an older LBC (with
their vented MCs) will be 'wet'. Since the silicone doesn't absorb
moisture from the air the way glycol does, it will essentially stay 'dry'
forever.
I've had the rear brakes on my TR3 hot enough to discolor the paint on the
wheels, and had no trouble with my many-years-old DOT 5 brake fluid boiling
!
I'll also point out that, on a 'real' hill, compression braking isn't
enough. I go down two 15% grades just going to and from work, they both
have 35 mph posted speed limits, and usually there is a patrolman watching
<g>
Randall
On Tuesday, May 04, 1999 11:23 PM, Egil Kvaleberg [SMTP:egil@kvaleberg.no]
wrote:
>
> On 3 May 1999, Chris DeStaffany wrote:
>
> > That may be true for the first few stops, but what about brake fade.
You
> > spend a day going up and down some pretty big hills and those brake
things
> > get really hot and don't work so pretty good anymore.
>
> No, not at all.
>
> You should use your gears to reduce and hold speeds on down-hills, not
the
> brakes. As long as the brakes get reasonable time to cool between uses,
> they will be OK.
>
> If brakes are applied constantly, they will overheat and fade, no matter
> how large they are.
>
> In addition to proper driving techniques, the most important limiting
> factor re. brake fade is definitely brake fluid boiling point. Even a
> little bit of humidity in it will reduce the boiling point dramatically.
> Change it every two years, at the very least. That will buy you more
> fading resistance than any increase in brake size.
>
> (Silicone fluids may get away with longer intervals, but they have a
> lower boiling point to start with).
>
> Egil
> who thinks he knows a thing or two about "pretty big hills".
> --
> Email: egil@kvaleberg.no Voice: +47 22523641, 92022780 Fax: +47 22525899
> Mail: Egil Kvaleberg, Husebybakken 14A, 0379 Oslo, Norway
> Home: http://www.kvaleberg.no/
>
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