Chassis; Bleeding The Brake System - Yamaha YZ450FX 2019 Owner's Service Manual

EAM20136

CHASSIS

EAM30227

BLEEDING THE BRAKE SYSTEM

EWA19140
WARNING
Bleed the brake system whenever:
• The system is disassembled.
• A brake hose is loosened, disconnected, or
replaced.
• The brake fluid level is very low.
• Brake operation is faulty.
1. Remove:
• Brake master cylinder cap
• Reservoir diaphragm
• Reservoir float (front brake)
• Protector (rear brake)
TIP
• Be careful not to spill any brake fluid or allow
the reservoir to overflow.
• Make sure that there is enough brake fluid be-
fore applying the brake. Ignoring this precau-
tion could allow air to enter the brake system,
considerably lengthening the bleeding proce-
dure.
• If bleeding is difficult, it may be necessary to let
the brake fluid settle for a few hours. Repeat
the bleeding procedure when the tiny bubbles
in the hose have disappeared.
2. Bleed the brake system.
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a. Fill the reservoir to the proper level with the
recommended brake fluid.
b. Install the reservoir diaphragm.
c. Connect the plastic hose "1" to the bleed
screw "2" securely, and place a container un-
der the end of the plastic hose.
2
A. Front
B. Rear
d. Slowly apply the brake several times.
e. Fully pull the brake lever or fully press down
the brake pedal and hold it in position.
f. Loosen the bleed screw.
TIP
Loosening the bleed screw will release the pres-
sure in the brake caliper and cause the brake le-
ver to contact the throttle grip or the brake pedal
to fully extend.
g. Tighten the bleed screw and then release the
brake lever or brake pedal.
h. Repeat steps (d) to (g) until all of the air bub-
bles have disappeared from the brake fluid in
the plastic hose.
TIP
During the procedure, keep adding brake fluid to
the reservoir.
ECA24320
NOTICE
• Wipe off any brake fluid on the brake discs,
tires, wheels, etc.
• Brake fluid may erode painted surfaces or
plastic parts. Always clean up spilled fluid
immediately.
i. Tighten the bleed screw.
1
j. Pour brake fluid to the reservoir up to the
specified level.
Refer to "CHECKING THE BRAKE FLUID
LEVEL" on page 3-26.
EWA13110
WARNING
After bleeding the hydraulic brake system,
check the brake operation.
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3-21

CHASSIS

2 2
1
Bleed screw
6 N·m (0.6 kgf·m, 4.4 lb·ft)