6.4
BRAKES
9923983 - 2012-2013 RZR 170 Service Manual
© Copyright 2012 Polaris Sales Inc.
HYDRAULIC BRAKE SYSTEM - OVERVIEW OF OPERATION
The Polaris brake system consists of the following components or assemblies: brake pedal, master cylinder, master
cylinder fluid reservoir, hydraulic brake lines, brake calipers, brake pads, and brake discs, which are secured to the drive
line.
When the brake pedal is applied, the master cylinder piston is forced inward. As piston moves inward, pressure is created
in the separate and sealed front and rear brake chambers inside the master cylinder. Pressure travels through the front
and rear brake lines and then to the pistons inside the brake calipers. The caliper pistons are forced outward against
the moveable brake pad. When the pad contacts the brake disc, the floating caliper bracket moves to force the stationary
brake pad against the disc, and the resulting friction reduces brake disc and vehicle speed.
As brake pads wear normally from friction, the caliper pistons move outward to compensate. Fluid from the master
cylinder reservoir fills the additional volume created in the caliper body as the pistons move outward (self adjusting
feature).
Fluid level in the reservoir is a critical maintenance item. If fluid level gets too low, air could enter the system and cause
poor brake performance or even brake system failure. If the fluid level is too high, pressure could build in the brake system
causing the brake pads to drag due to fluid expansion.
Brake fluid and brake system parts expand and contract due to the heating and cooling during normal operation. A very
small hole called the compensating port, located inside the master cylinder, is opened and closed by the master cylinder
piston. When the brake pedal is released, the piston returns to its rest position and the compensating port is open. This
allows expanding or contracting fluid to move back and forth between master cylinder and fluid reservoir, preventing a
buildup of pressure in the system.
It is very important that the master cylinder reservoir have adequate space to allow for fluid expansion. Never overfill the
reservoir. Do not fill it beyond the MAX LEVEL line!
When servicing Polaris brake systems use only Polaris DOT 4 Brake Fluid (PN 2872189). 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 property is desirable in order to reduce
the chance of corrosion (due to moisture) in the brake system. But an open container of fluid will absorb moisture from
the environment. When brake fluid contains moisture the boiling point is reduced, which can lead to early brake fade and
the possibility of serious injury. Brake fluid must be changed with fresh fluid from a sealed container at recommended
intervals or if contaminated.