Hydraulic Brake System Operation - Polaris RANGER XP 700 4X4 Service Manual

BRAKES

HYDRAULIC BRAKE SYSTEM OPERATION

Typical Hydraulic Brake System
Must be clear to allow
proper diaphragm
movement
The Polaris brake system consists of the following components or assemblies: brake pedal; master cylinder; hydraulic hose; brake
calipers (slave cylinder); brake pads; and brake discs, which are secured to the drive line.
When the foot 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 (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 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 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 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. Never overfill the reservoir! Do not fill the reservoir past the MAX
LEVEL line!
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 brake systems use only Polaris DOT 4 Brake Fluid (P/N 2872189). Polaris brake fluid is sold in 12 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. This causes the boiling temperature
of the brake fluid to drop, which can lead to early brake fade and the possibility of serious injury.
9.4
F
B
A
Movable
G
Brake Pad
Compensating port compensates
E
for temperature changes by allowing
fluid back to master cylinder.
C
D