Date:         Tue, 30 Sep 2008 08:53:08 -0700
Reply-To:     Don Hanson <dhanson@GORGE.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Don Hanson <dhanson@GORGE.NET>
Subject:      RE thread on brakes, Dot3,4, etc.(long post)
Content-Type: text/plain; charset="Windows-1252"

  A little on brakes, for general information.

  When brakes "overheat", a couple of different things happen.  A couple of
different causes of poor stopping.

  The most common, probably, is what is commonly known as "Brake
fade"...when the pedal sinks to the floor while you're trying to stop.
Descending a long mountain pass or grade, heat builds up in the brakes.
This heat causes your brake fluid to boil.  Actually, it causes any moisture
in the brake fluid to boil, rarely the fluid itself.  Water turns to steam
at 212 deg f. and steam is mostly air....So you're brake cylinders and lines
are full of steam, not brake fluid. A very little amount of moisture can
cause a large amount of steam.. That is why you should change the brake
fluid...make sure there is no moisture in there...and brake fluid loves to
suck up moisture.  If you have tainted brake fluid...it matters not whether
it's DOT 3 or 4 or Dot Bazillion...the water in it will boil at 212f anyhow.

  The second way we encounter poor braking is when the brakes get really hot
but the fluid is fresh. There is no way around this phenom.... Brake linings
are composed to be most effective in a certain temperature range.  When they
exceed that temp. they lose some of their friction..This happens in a small
'temp window'.  One minute, everything is working fine, the next, your
brakes just don't seem to be slowing you down as effectively.  When you
encounter "overheating brakes" you pedal still feels right...no "fade" or
slowly sinking pedal, and pumping the brakes won't really help you get more
stopping power. After encountering this a few times, you may be able to
detect the onset of this and reduce the demands on your brakes till their
temperature goes back down. It is a bit subtitle to "feel"
 If you do encounter overheating brakes...You either have to let them cool
by stopping and waiting or by selecting a lower gear and letting the engine
take some of the braking load.  If you have really hot brakes, be careful
when you do come to a full stop..they may even (rarely) catch fire..If you
are forced to wait while they cool off, do not use your parking brake and
after a few minutes, let the vehicle roll a few feet to allow the drums and
discs to cool evenly..
 Brakes for street vehicles use a lining compound that works best at low-ish
temperatures.  Your brakes have to work at the bottom of your driveway when
you start out to work in the A.M. ...And they have to last.  Hence, we get
hard compounds that are effective at 'cold' temps. for our street vehicles
but don't work well at real high temps.  If you've ever watched a sports car
race (LeMan 24hr, etc) you will have seen "Glowing brakes" on the
cars...They use a compound that wouldn't probably stop you very well on the
way to the soccer field, but a 1500degrees, it's  still working well.
  The most effective method of minimizing heat build-up in your brakes
during a long grade is to brake 'forcefully' in short applications, then
remove your foot from the brake pedal.  Repeat as needed.  You may get some
'looks' from other clueless drivers, but the Truckers will know exactly what
you are doing.   This "periodic braking"  allows the brake system components
to cool as much as possible, between brake applications,  by taking them out
of contact with each other.  If you brake the whole hill but just enough to
keep your speed steady..your brakes will simply build heat all the way.  If
you do have a capable gearing set-up and are toting an extra load down a
steep hill, it is effective to simply slow up and select a lower gear to
help you descend.

  Don Hanson