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HYDRAULIC BRAKE SYSTEM
OPERATION OVERVIEW
Typical Hydraulic Brake System
Must be clear
to allow
proper dia-
phragm move-
ment
F
B
A
Move-
able
Brake
Pad G
The Polaris disc brake system consists of the
following components or assemblies: brake lever;
master cylinder; hydraulic hose; brake calipers (slave
cylinder); brake pads; and brake discs, which are
secured to the drive line.
When the hand activated brake lever (A) is applied it
contacts piston (B) within the master cylinder. As the
master cylinder piston moves inward it closes a small
opening (compensating port C) within the cylinder and
starts to build pressure within the brake system. As
the pressure within the system is increased, the piston
(D) located in the brake caliper moves outward and
applies pressure to the brake pad. This pad contacts
the brake disc and moves the caliper in its floating
bracket, pulling the stationary side pad into the brake
disc. The resulting friction reduces brake disc and
vehicle speed. As the lever pressure is increased, the
braking affect is also increased.
The friction applied to the brake pads will cause the
pads to wear. As these pads wear, the piston within
the caliper moves further outward and becomes self
adjusting. Fluid from the reservoir fills the additional
area created when the caliper piston moves outward.
Brake fluid level is critical to proper system operation.
Too little fluid will allow air to enter the system and
cause the brakes to feel spongy. Too much fluid could
cause brakes to drag due to fluid expansion.
Located
within
the
compensating port (C) which is opened and closed by
the master cylinder piston assembly. The port is open
9.4
Compensating port
compensates
E
for temperature
changes by allow-
ing fluid back to
C
master cylinder
D
master
cylinder
is
the
when the lever is released and the master cylinder
piston is outward. As the temperature within the
hydraulic system changes, this port compensates for
fluid expansion (heated fluid) or contraction (cooled
fluid). During system service, be sure this port is
open. Due to the high temperatures created within the
system during heavy braking, it is very important that
the master cylinder reservoir have adequate space to
allow for fluid expansion.
reservoir! Fill to 1/4² - 5/16² (.64 - .80 cm) from top
of the cylinder.
This system also incorporates a diaphragm (E) as part
of the cover gasket; and a vent port (F) located
between the gasket and the cover. The combination
diaphragm and vent allow for the air above the fluid to
equalize pressure as the fluid expands or contracts.
Make sure the vent is open and allowed to function.
If the reservoir is over filled or the diaphragm vent is
plugged the expanding fluid may build pressure in the
brake system leading to brake failure.
When servicing Polaris ATV brake systems, use only
Polaris DOT 3 Brake Fluid (PN 2870990).
WARNING: Once a bottle is opened, use what is
necessary and discard the rest in accordance with
local laws. Do not store or use a partial bottle of brake
fluid. Brake fluid is hygroscopic, meaning it rapidly
absorbs moisture.
This causes the boiling
temperature of the brake fluid to drop, which can lead
to brake fade and the possible loss of control.
HYDRAULIC
CALIPER BLEEDING
This caliper is a single piston design. The caliper
pistons are "T"-shaped, which allows both hand and
foot brake to use the same caliper piston, but remain
separated by seals. The hand brake system applies
hydraulic pressure to both front calipers and only the
outer diameter of the rear caliper pistons.
auxiliary (foot) brake applies pressure to the inner
portion of the rear caliper pistons. Because the hand
and foot brake hydraulic systems are separate, there
are also two bleed screws -- one for the outer fluid
chamber (hand brake), and one for the inner fluid
chamber (foot brake).
bleeding the brake system is the same as outlined on
page 9.4 - 9.5, however, each system must be bled
separately.
Hydraulic Auxiliary Brake inspection and adjustment
is outlined in Chapter 2 beginning on Page 2.27.
BRAKES
BRAKES
Never overfill the
The
The basic procedure for
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