Yamaha YZF-R125 Service Manual: Bleeding the hydraulic brake system

WARNING

Bleed the hydraulic 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.

NOTE:

  • Be careful not to spill any brake fluid or allow the brake master cylinder reservoir or brake fluid reservoir to overflow.
  • When bleeding the hydraulic brake system, make sure there is always enough brake fluid before applying the brake. Ignoring this precaution could allow air to enter the hydraulic brake system, considerably lengthening the bleeding procedure.
  • 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.

1. Bleed:

  • Hydraulic brake system

a. Fill the brake fluid reservoir to the proper level with the recommended brake fluid.

b. Install the diaphragm (brake master cylinder reservoir or brake fluid reservoir).

c. Connect a clear plastic hose "1" tightly to the bleed screw "2".

Bleeding the hydraulic brake system


A. Front

B. Rear

d. Place the other end of the hose into a container.

e. Slowly apply the brake several times.

f. Fully pull the brake lever or fully press down the brake pedal and hold it in position.

g. Loosen the bleed screw.

NOTE:

Loosening the bleed screw will release the pressure and cause the brake lever to contact the throttle grip or the brake pedal to fully extend.

h. Tighten the bleed screw and then release the brake lever or brake pedal.

i. Repeat steps (e) to (h) until all of the air bubbles have disappeared from the brake fluid in the plastic hose.

j. Tighten the bleed screw to specification.


k. Fill the brake fluid reservoir to the proper level with the recommended brake fluid.

Refer to "CHECKING THE BRAKE FLUID LEVEL" on page 3-18.

WARNING

After bleeding the hydraulic brake system, check the brake operation.

    Checking the rear brake hose
    1. Check: Brake hoses "1" Cracks/damage/wear  Replace. 2. Check: Brake hose holder "2" Loose connection Tighten the holder bolt. Loose or open holder Fasten properly ...

    Adjusting the drive chain slack
    NOTE: The drive chain slack must be checked at the tightest point on the chain. CAUTION:A drive chain that is too tight will overload the engine and other vital parts, and one that ...

    Other materials:

    Checking the piston rings
    1. Measure: Piston ring side clearance Out of specification Replace the piston and piston rings as a set. NOTE: Before measuring the piston ring side clearance, eliminate any carbon deposits from the piston ring grooves and piston rings. 2. Install: Piston ring (into the cylind ...

    Checking the primary driven gear
    1. Check: Primary driven gear "1" Damage/wear Replace the primary drive gear and clutch housing as a set. Excessive noise during operation  Replace the primary drive gear and clutch housing as a set. ...

    Installing the front brake master cylinder
    1. Install: Brake master cylinder "1" Brake master cylinder holder "2" NOTE: Install the brake master cylinder holder with the arrow mark "a" pointing forward. Align the end of the brake master cylinder holder with the punch mark "b" on the handlebar. First, tighten the front bo ...

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