Hydraulic Brake System Overview; Compensating Port - Polaris INDY TRAIL RMK Service Manual

BRAKES / FINAL DRIVE

Hydraulic Brake System Overview

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A
The Polaris snowmobile hydraulic brake system consists of the following components or assemblies: brake lever,
master cylinder, hydraulic hose, brake caliper (slave cylinder), brake pads, and a brake disc which is secured to
the drive line.
When the hand activated brake lever (A) is applied, it contacts a piston (B) within the master cylinder. As the
master cylinder piston moves inward it closes a small opening called a 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, moves the caliper in its floating bracket and pulls the stationary pad into the brake disc. As the lever
pressure is increased, the braking effect is increased.
The friction applied to the brake pads will cause the pads to wear. As the pads wear, the piston within the caliper
self-adjusts and moves further outward.
Brake fluid level is critical to proper system operation. A low fluid level allows air to enter the system causing the
brakes to feel spongy.

Compensating Port

Located within the master cylinder is a small compensating port (C) which is opened and closed by the master
cylinder piston assembly. The port is open when the brake lever is released and the piston is outward. As the
temperature within the hydraulic system changes, this port compensates for fluid expansion caused by heat, or
contraction caused by cooling. 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 the brake fluid to expand. Master cylinder reservoirs should be filled to the top of the
fluid level mark on the inside of the reservoir, 1/4² - 5/16² (.6 - .8 cm.) below lip of reservoir opening.
WARNING
Never overfill the reservoir. This could alter brake function, resulting in system component damage or sever
personal injury or death.
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. Be sure the vent is open and allowed to function. If the reservoir is overfilled or
the diaphragm vent is plugged, the expanding fluid may build pressure in the brake system and lead to brake
failure.
8.8
E
F
B
D
C