The truth about
brake fluid |
Richard Oliver |
To
Stop or Not ?
The efficient operation of
a vehicle's braking system is the most important consideration before setting
the wheels of a motor vehicle in motion. Just about everything that's on
the new car market these days provides the motorist with more than enough
power to get them off the mark and take them over that government revenue
generating speed limit before they realise.
Now the hard part-how to stop
that vehicle with the same degree of efficiency and control that the vehicle
had when it was new. The question relates to how efficient is the braking
system on the vehicle when it's a little older, say 12 months, and it has
travelled some 30,000 kilometres. That leads to the most overlooked component
of a vehicle braking system-The Brake Fluid. Vehicle and brake fluid
manufacturers recommend that the brake fluid be changed periodically. Brake
fluid is Hygroscopic-it attracts and absorbs water. This is unavoidable.
It is part of brake fluid's chemistry and even though it is in a "closed"
system, the attraction for water is so strong that it is still absorbed.
When brake fluid absorbs water, its boiling point is reduced. A good quality
fluid, having a boiling point of say 260øC when new, could, over two
years have its boiling point gradually reduced to about 160øC. This
deterioration continues and eventually the heat produced by friction between
the brake lining materials and discs or drums may vaporise the fluid. Vapour,
unlike liquid, is compressible, so pressing the brake pedal merely compresses
vapour instead of operating the brakes. (This is known as the vapour lock
point and it is slightly lower than boiling point). This kind of brake failure
can only be avoided by changing the brake fluid regularly. How often should
brake fluid be changed? Brake fluid deteriorates not with distance but with
time. It continues to absorb water even when the vehicle is stationary.
Most vehicle manufacturers
recommend regular brake fluid changes on a time basis, eg. every year.
Unfortunately, such recommendations are not always followed and independent
surveys have shown that many vehicles have dangerous brake fluid in them.
Vehicle manufacturers also specify the brake fluid performance required,
usually by reference to a DOT specification, and brake fluid should therefore
always be changed before it "falls out" of specification. DOT specifications
include minimum boiling point requirements and measurement of boiling point
is one of the best ways to determine whether or not fluid needs changing.
With the price of good quality brake fluid below $14 per litre it makes good
sense to change it on a regular basis. |