Hydraulic Brake System Operation - Polaris Magnum 2x4 Service Manual

Typical Hydraulic Brake System
Must be clear to allow
~
proper diaphragm
movement ______
F
A
B
E
BRAKES
Hydraulic Brake System Operation
Compensating port compensates
for temperature changes by allowing
fluid back to master cylinder
C---------
Moveable
-1
0--"'"
Brake Pad
G
r=-~~
The Polaris brake system consists of the following components or assemblies: brake lever; master cylinder; hy-
draulic 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 a piston (8) within the master cylinder. As the mas-
ter 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 moveable 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 in-
creased.
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 master cylinder is the compensating port (C) which is opened and closed by the master cylinder
piston assembly. The port is open 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 con-
traction (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. Never overfill the reservoir! Fill to 1/4" - 5/16" (.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 pres-
sure 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 high temperature brake fluid (PN
2870990).
Polaris brake fluid is sold in 5.5 oz. bottles. 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 from the air. This causes the boiling temperature of the brake
fluid to drop, which can lead to early brake fade and the possibility of serious injury.
Polaris Industries Inc. 9.3
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