Hydraulic Brakes - Honda Motorcycle Service Manual

The drum thickness is relatively thin, which further aids heat
conductivity, and must not be machined i n a brake lathe. If the
drum surface is severely damaged, the hub must be replaced.
BRAKES
HYDRAULIC BRAKES
Brake Fluid
The designations DOT 3 and DOT 4 specify the brake fluid's
ability to withstand heat without boiling. The greater the
number, the higher the boiling point. It is necessary for the
brake fluid t o have a high boiling point so that the fluid does
not boil within the brake line due t o the high temperature o f the
brake discs and components. Boiling brake fluid leads to a
drastic loss of braking force due t o the air bubbles that form
within the brake lines.
It is vital for brake systems t o quickly dissipate the heat that is
generated by the friction of the braking action so their stop-
ping force remains consistent. Since drum brakes contain
almost all of the brake components within the wheel hub, it is
important that these brake components be made of materials
that conduct heat rapidly. It is just as important that the brake
is of the proper size for the anticipated requirements of the
vehicle.
In order to enhance heat conductivity while providing accept-
able wear resistance on the inner surface of the brake drum,
the drum itself is made of cast iron. The remainder of the
drumlhub is made of aluminum alloy with cooling fins cast into
the outer circumference; again for heat conductivity and
Never mix DOT 3 and DOT 4 brake fluid within a system. It is
important t o add only the same DOT number and even the
same brand of brake fluid when adding fluid. If you are unsure
of the type within the system, drain the system and refill it
with DOT 4; systems designed for DOT 3 can use DOT 4. But
DOT 4 systems must never be filled with DOT 3. DOT 4
systems generate greater heat and thereby require the higher
boiling point characteristic of DOT 4.
DRUM BRAKE
RAKE SHOE
HUB
Avoid mixing different brands of brake fluid. Improper mixing
such as this may lead to chemical decomposition and
contamination.
dispersion, but also for reduced unsprung weight. To speed
conductivity, the cast iron drum is captured within the
aluminum hub and cannot be removed.
It is also important to use only fresh brake fluid from a sealed
container. Once a new container of brake fluid is opened, be
sure t o reseal it tightly and plan on discarding the fluid after six
months. This is because brake fluid left in the container tends
to absorb moisture from the air; it is hydroscopic. Moisture can
form even within a sealed brake system because of this par-
ticular property. Moisture in the brake fluid contaminates the
brake system and lowers the boiling point of the fluid. It also
corrodes the brake cylinders and pistons, which eventually
causes seal damage and leakage.
For this reason you should note the date o n the container
when i t is first o ~ e n e d for later reference.
Date of Issue: March.
1995
o
HONDA MOTOR CO.,LTD.
17-3