Brake System Service Notes; Brake System Operation - Polaris Sportsman 850 Service Manual

BRAKE SYSTEM

BRAKE SYSTEM SERVICE NOTES

Disc brake systems are light weight, low maintenance,
and perform well in the conditions this vehicle will
routinely encounter. There are a few things to remember
when replacing disc brake pads or performing brake
system service to ensure proper system function and
maximum pad service life.
• DO NOT over-fill the master cylinder fluid reservoir(s).
• Make sure the brake lever / pedal returns freely and
completely.
• Adjust stop pin on calipers after pad service.
• Check and adjust master cylinder reservoir fluid level
after pad service.
• Make sure atmospheric vent on reservoir is
unobstructed.
• Test for brake drag after any brake system service and
investigate cause if brake drag is evident.
• Make sure caliper moves freely on guide pins (where
applicable).
• Inspect caliper piston seals for foreign material that
could prevent caliper pistons from returning freely.
• Perform a brake burnishing procedure after installing
new pads to maximize service life.
• DO NOT lubricate or clean the brake components with
aerosol or petroleum products. Use only approved
brake cleaning products.
• DO NOT allow brake cleaning products to contact
painted surfaces. Paint damage will occur as a result.
9.4

BRAKE SYSTEM OPERATION

The brake system consists of the following components
or assemblies: hand brake master cylinder w/lever, foot
brake master cylinder w/pedal, brake fluid reservoirs,
brake lines, brake calipers, brake pads, and brake discs,
which are secured to the drive line.
When the brake lever or pedal is applied, it moves the
hydraulic piston within the master cylinder. As the piston
moves inward it closes a small opening (compensating
port) within the cylinder and starts to build pressure
within the brake system. As the pressure within the
system is increased, the pistons located in the brake
calipers move outward and apply pressure to the
moveable brake pads. These pads contact the brake
discs and move the calipers in their floating bracket,
pulling the stationary side pads into the brake discs. The
resulting friction reduces brake disc and vehicle speed.
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 which is opened and closed by the master cylinder
piston assembly. As the temperature within the hydraulic
system changes, this port compensates for fluid
expansion or contraction. 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! Do not fill the reservoir 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 causes the
boiling temperature of the brake fluid to drop, which can
lead to early brake fade and the possibility of serious
injury.